- Email: [email protected]
Effects of Combined Curves on Driver's Speed Behavior: Driving Simulator Study
Available online at www.sciencedirect.com
ScienceDirect Transportation Research Procedia 3 (2014) 100 – 108
17th Meeting of the EURO Working Group on Transportation, EWGT2014, 2-4 July 2014, Sevilla, Spain
Effects of combined curves on driver’s speed behavior: driving simulator study Francesco Bella * Roma TRE University - Department of Engineering, via Vito Volterra n. 62 - 00146 Rome, Italy
Abstract The probability to occur in drive perception errors increases as the complexity of the road alignment increases. In particular perceptions errors could be significantly relevant in the conditions of horizontal curves overlapped with sag vertical curves (sag combinations or combined curves). The highway geometric design guidelines of several Countries provide suggestions for the coordination of the sag combinations in order to avoid combined configurations which can bring to undesirable optical effects and a reduced safety. Such suggestions come from studies based on the drawing of the perspective of the road. This drawing method is heavily limited with regards to the simulation of the perspective view of the highway to the driver during the dynamic task of the driving. Interactive driving simulation methods are deemed to be more efficient for these aims. This paper reports the results of a study carried out using an interactive driving simulator and aimed at evaluating the effects on the driver’s speed behavior of different configurations of sag combinations and non-combined curves on flat grade with the same features as the horizontal curves of the sag combinations (reference curves). The main result was that on suggested sag combinations the driver’s speed behavior did not differ in any statistically significant way from that on the reference curves. Whereas the critical sag combinations (configurations that should be avoided) caused a high reduction in speed along the tangent–curve transition, which pointed the driver’s reaction to the wrong perception of the road alignment This result, therefore, confirmed the effectiveness of the road design guidelines for the coordination of horizontal curves and sag vertical curves. © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license © 2014 The Authors. Published by Elsevier B. V. (http://creativecommons.org/licenses/by-nc-nd/3.0/). Committee of EWGT2014. Selectionand andpeer-review peer-review under responsibility the Scientific under responsibility of the of Scientific Committee of EWGT2014 Selection Keywords: driving simulator; road safety; driver behavior; combined curves
* Corresponding author. Tel.: +39-06-57.33.34.16; fax: +39-06-57.33.34.41 E-mail address: [email protected]
2352-1465 © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Scientific Committee of EWGT2014 doi:10.1016/j.trpro.2014.10.095
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
101
1. Introduction Curves are the geometric element of the road alignment characterised by the greater risk of accidents. According to the Fatality Analysis Reporting System (FARS), since 2005, about 5000 fatalities each year have resulted from single-vehicle run-off-road crashes on the horizontal curve sections of 2-lane rural roads in the United States (National Highway Traffic Safety Administration, 2011). Such statistics are deemed to be due to the erroneous perception of the features of the alignment that induces drivers to assume an inadequate behavior compared to the geometric design of the curved section (Cartes, 2002). Several researches have pointed out that the occurrence of erroneous perception increases as the complexity of the alignment increases and that erroneous perception could be significantly relevant in the conditions of horizontal curves overlapping with sag vertical curves or with crest vertical curves (Smith and Lamm, 1994; Mori et al., 1995; Wooldridge et al., 2000; Bidulka et al., 2002). In particular Smith and Lamm (1994) hypothesized that an overlapping crest curve may cause the horizontal curve to look sharper while a sag curve may cause the horizontal curve to look flatter than it actually is (called driver perception hypothesis). Then the driver may adopt a lower or higher speed, respectively, than if the radius were on a flat grade. Therefore the erroneous perception of the horizontal curve may be particularly hazardous for the horizontal curve overlapping with sag vertical curve (called combined curve or sag combination) where the drivers may perceive a sharp curve as a flat one. The road design guidelines of several Countries (e.g. Italy, Spain, USA) (Ministry of Infrastructures and Transports, 2001; Ministerio de Fomento, 2001; AASHTO, 2011), as a priority, invite to avoid the overlapping of horizontal and sag vertical curves and, if not possible, they affirm the need to overlap the vertices and to design vertical and horizontal curves with lengths of the same order of magnitude (here called suggested sag combination). In addition, the guidelines suggest to avoid sag combination formed by horizontal curve just after the end of the sag vertical curve, because this configuration (here called critical sag combination) causes important undesirable optical effects. These suggestions come from studies based on the drawing of the perspective of the road. This drawing method is deemed to be heavily limited, because it does not allow to simulate the perspective view of the road to the driver during the dynamic task of the driving. Therefore, in the last decade, numerous studies on the visual perception of the road were carried out by mean of the most advanced computer animation techniques (Bidulka et al., 2002; Hassan and Sayed, 2002; Hassan et al., 2002; Hassan and Easa, 2003; Hassan, 2004). However, such visualization techniques are non-interactive and do not allow to evaluate the driver’s reaction to its perception of the road scenario. The driving simulation is deemed to be the most accurate method in order to study the drivers perception (e.g. Lamm et al., 1999; Bella, 2009). Driving simulators offer several advantages such as low costs entailed in carrying out experiments, easy data collection, the utmost safety for test drivers, the possibility of carrying out experiments in controlled conditions. Besides such important benefits, driving simulators are interactive. They allow the test driver to manipulate the pedals and steering wheel of the vehicle during the task of driving and allow the recording of the effects of the road configurations on driver behavior in terms of speeds, trajectory, braking, and the like. Such features are the reason for the growing use of driving simulators for modeling driver visual demand on threedimensional highway alignments (Easa and Ganguly, 2005; Easa and He, 2006), for testing the effectiveness of road treatments on rural roads with crest vertical curves (Rosey et al., 2008; Auberlet et al., 2010; Auberlet et al., 2012) as well as for evaluating the effect of the interaction between overlapping horizontal and vertical alignments (Garcia et al., 2011; Hassan and Sarhan, 2012; Bella, 2014). The experimental study at the driving simulator reported here was carried out in order to provide an additional and even more reliable validation of the guideline indications for the coordination of horizontal curves overlapping with sag vertical curves. More specifically the aim of the study was to asses if such suggestions are able to determine: x on the suggested sag combinations, a driver’s speed behaviour that is not significantly different from that on the non-combined curves on flat grade with the same features as the horizontal curves of the sag combinations (called reference curve); x on the critical sag combinations, a driver’s speed behaviour that is significantly different (more critical for the road safety) from that on the suggested sag combinations.
102
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
For this purpose, the driver’s speed behaviour of each driver along the tangent-curve transition was recorded. More specifically, the difference in speed between the point on the approach tangent located 200 m from the beginning of the horizontal curve and the midpoint of the curve was analyzed. This because, according the literature (e.g. Lamm et al. 1988; Misaghi and Hassan, 2005; Bella, 2007; Bella 2008a), the speed reduction between successive locations of the road alignment increases as the driver detects undesirable optical effects or unclear and non-timely information provided by the road. 2. Method A within-subjects design was carried out using the fixed-base driving simulator of the Inter-University Research Centre for Road Safety (CRISS). On the basis of the speed data collected on the tangent-curve transitions of reference curves and sag combinations, one-way repeated MANOVA was performed to evaluate if the driver’s speed behavior on the horizontal curves was influenced by the type of curve (i.e. different configurations of sag combinations and reference curves). It should be noted that driving simulators do have one important limit. Drivers do not perceive any risk in a driving simulator. The driver’s awareness of being immersed in a simulated environment might give rise to a behavior which is different than that on a real road. However, several simulator validation studies have afforded us sufficient guarantees as regards the relative validity, which refers to the correspondence between effects of different variations in the driving situation. Absolute validity, which refers to the numerical correspondence between behavior in the driving simulator and in the real world, is not essential, whenever the research is dealing with matters relating to the effects of independent variables (Tornos, 1998). For the purpose of the present study, only relative validity is required and the CRISS driving simulator has been previously validated as a useful tool for studying driver’s speed behavior on two-lane rural roads (Bella, 2008b). This evidence has also allowed us to successfully use the CRISS driving simulator for studying the driver behavior induced by road configurations as well as for providing insights that may help to guide road design of two-lane rural roads (e.g. Bella, 2011; Bella, 2013; Bella, 2014b; Bella, 2014c; Bella and D’Agostini, 2010; Bella and Russo, 2011; Bella and Calvi, 2013). 2.1. Road scenarios, sag combinations and reference curves Two two-lane rural roads, about 15 km long, were designed. The cross-section was 10.50m wide, formed by two 3.75m wide lanes and two 1.50m wide shoulders. The values of the circular curves’ radius ranged from 118m to 800m. The length of tangents ranged from 150m to 2200m, while the deflection angle of horizontal curves ranged from 30° to 80°. The longitudinal grades were not over 6%. Italian guidelines assume for these roads a design speed ranged between 60 km/h (on curve with radius equal to 118m) and 100 km/h (on tangent). The posted speed limit is 90 km/h. These roads had the following types of sag combinations (fig. 1): x suggested sag combination: the sag vertical curve is overlapped to horizontal curve so the vertices of the two curves coincided and their length was the same order of magnitude, as required by design guidelines for the coordination of horizontal alignment and profile (Ministry of Infrastructures and Transports, 2001); x critical sag combination: the horizontal curve begins just after the end of the sag vertical curve. The their length was the same order of magnitude. The guidelines (Ministry of Infrastructures and Transports, 2001) suggest to avoid this configuration because it causes anomalies of the perspective of the road alignment. Such sag combinations and reference curves (non-combined curves on flat grade with the same features as the horizontal curves of the sag combinations) were the curves of interest. Half of these curves were on the first road and the other half was on the second alignment. This in order to: x limit the order effect induced by the same sequence of presentation of the curves to the driver (the two road scenarios were driven by drivers in a counterbalanced order); x limit the duration of tests in the driving simulator and consequently limit the potential effects of fatigue on the driver (see also the next section Procedure and participants).
103
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
The geometric parameters of the curves are shown in table 1, while figure 1 shows the configurations of the two types of sag combination. Table 1. The Geometric features of the references curves and sag combinations Horizontal curve Lcirc La.t.
J
Rv
Lv
ia
id
'i
400
400
77°
-
-
0
0
0
800
800
65°
-
-
0
0
0
200
400
400
77°
11430
400
-2.0
1.5
3.5
180
300
800
800
65°
9566
660
-4.0
2.9
6.9
140
200
400
400
77°
11430
400
-2.0
1.5
3.5
180
300
800
800
65°
9566
660
-4.0
2.9
6.9
Lc
Lcl
Reference curves
252
480
140
200
437
660
180
300
Suggested sag combinations
252
480
140
437
660
252
480
437
660
Critical sag combinations
Vertical curve Ld.t.
R
R = radius of horizontal curve
J = deflection angle
Lc = length of horizontal curve in m
Rv = radius of vertical curve in m
(Lcl+Lcirc+Lcl)
Lv = length of vertical curve in m ia = approach grade in percent
Lcl = length of clothoids in m Lcirc = length of circular curve in m
id = departure grade in percent
L a.t. = length of approach tangent in m
'i=~id-ia~
L d.t. = length of departure tangent in m
Fig. 1. Configurations of sag combinations: suggested and critical
104
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
2.2. Apparatus The CRISS simulation system is an interactive fixed-base driving simulator. The system allows to represent the infrastructure scenario, traffic conditions, configurations of horizontal and vertical alignments, cross section features, and to simulate the friction between tires and road surface and the vehicle’s physical and mechanical characteristics. The hardware interfaces (wheel, pedals and gear lever) are installed on a real vehicle. The driving scene is projected onto three screens; one in front of the vehicle and two on each side. The usual field of view is 135°. The scenario is updated dynamically according to the travelling conditions of the vehicle, depending on the actions of the driver on the pedals and the steering wheel. The resolution of the visual scene is 1024x768 pixel and the update rate is 30-60 Hz depending on scene complexity. The system is also equipped with a sound system that reproduces the sounds of the engine. This setup provides a realistic view of the road and surrounding environment. The system allows the intensity of driver actions on the brake, accelerator pedal, and steering wheel to be recorded and provides many parameters to describe travel conditions (e.g., vehicle barycenter, relative position in relation to the road axis, local speed and acceleration, steering wheel rotation angle, pitching angle, rolling angle). All the data can be recorded at time or space intervals of a fraction of a second or a fraction of a meter. Figure 2 shows an example of the road scenario as seen by the driver during the driving simulation. 2.3. Procedure and participants The experiment was carried out using dry pavement conditions in good state of maintenance and with the free vehicle on its own driving lane. Whereas, on the driving lane a modest traffic was distributed randomly for the sole purpose of inducing the driver not to invade it. The vehicles in the opposite lane were always present in those sections set away from the curves of interest. The simulated vehicle was a standard medium class car, both for dimension and for mechanical performance, with an automatic gear. The data recording system acquired all the parameters at spatial intervals of 5 m. The driving procedure was broken down into the following steps: (a) communicate to the driver about the duration of the driving and the use of the steering wheel, pedals, and automatic gear; (b) train as to how to use the driving simulator on a specific alignment for approximately 10 min to allow the driver to become familiar with the simulator’s control instruments; (c) execute the first test scenario; (d) have the driver vacate the car for about 5 min so as to reestablish a psychophysical state similar to the one at test start and to fill out a form with personal data (e.g., years of driving experience, average annual distance driven); (e) execute the second test scenario; and (f) have driver answer a questionnaire as to any discomfort perceived during the driving procedure, including the type (e.g. nausea, giddiness, daze, fatigue, other) and the intensity (e.g. null, light, medium, high). Participants were instructed to drive as they normally would in the real world. Thirty-five drivers were selected to perform the driving in the simulator according to the following characteristics: no experience with the driving simulator, at least four years of driving experience and an average annual driven distance on rural roads of at least 2500 km.
Fig. 2. Driving phase from the simulator
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
105
The participants, male (63%) and female (37%), ranged from 23 to 60 years of age (average 26). From the analysis of the questionnaire filled in by the drivers at the end of the test, it emerged that no participants experienced any discomfort condition. No participant therefore was excluded from the sample. The sequence of the two scenarios was varied for each driver, so as to avoid any influences that might result from the repetition of the experimental conditions in the same order. The participants completed the procedure in less than 60 minutes. 2.4. Data collection For each sag combination and reference curve, the speeds of the drivers were recorded along the section formed by the last 200 m of the approach tangent and the horizontal curve. More specifically, the following local speeds of each driver were collected (fig 3): x speed (VT) at the point (T) on the approach tangent located 200 m from the beginning of the horizontal curve; x speed (VC) at the midpoint (C) of the horizontal curve; x the difference of speed ('VT-C) between VT and VC. VT was analyzed in order to ascertain whether or not, driver’s speed at point T, was unaffected by the type of the successive curve. It should be noted that the choice of this point is consistent with the results of Fitzpatrick et al. (2000) who found that the speed along the approach tangent does not begin to drop until at a point closer than 200 m to the point of curvature. Should it be confirmed, as expected, that VT does not depend on the type of curve, the possible difference between the values of VC and 'VT-C on the different successive curves (sag combinations and reference curves) shall exclusively depend on the conditioning induced by the type of curve. VC and 'VT-C were analyzed to ascertain if the drivers’ speed behavior on the section of tangent-curve transition was affected by the type of the curve. 3. Data analysis and results In order to evaluate the effects on the driver’s speed behaviour induced by the 2 types of sag combination and reference curves, a repeated measures MANOVA was performed. More specifically, one-way repeated measures MANOVA was carried out in order to investigate the effects on the two dependent variables (VT and 'VT-C) due to the independent variable (or factor) type of curve (3 types: reference, and 2 types of sag combination: suggested and critical). It should be noted that VC was not used as dependent measure in MANOVA test in order to avoid redundancy in the dependent variables. Figure 4 shows the mean values of the dependent measures VTand'VT-C and their 95% confidence intervals for every type of curve. The VC values are also shown. The MANOVA revealed a significant effect for type of curve (F(6,272) = 14.616, P = 0.000). Univariate statistics (Mauchly’s test revealed that the assumption of sphericity was ascertained for VT, while for 'VT-C a Greenhouse– Geisser correction was used) showed that the type of curve did not affect the dependent measure VT (F(1.749, 120.710) = 1.886, P = 0.161), while it significantly affected the dependent measure 'VT-C (F(2, 138) = 3.811, P= 0.024).
Fig. 3. Locations where speed data were collected
106
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
Fig. 4. Mean values of VT, VC and'VT-C for reference curves and sag combinations (bounds of 95% confidence interval are also shown)
Hence, having ascertained that VT is not affected by the driver’s perception of the type of curve, it is possible to affirm that the difference between the values of 'VT-C depends entirely on the conditioning induced by the type of curve. Post hoc tests using the Bonferroni correction revealed that the mean value of 'VT-C (17.1 km/h) on reference curves was not significantly different than that (16.8 km/h) on suggested sag combinations (mean difference= 0.3km/h; P= 1.000). The mean value of 'VT-C on reference curves (17.1 km/h) was less than the mean value (22.0 km/h) on critical sag combinations, however the difference was not statistically significant (mean difference = 4.9 km/h; P = 0.125). The difference between the mean value of 'VT-C on suggested sag combinations and that on critical sag combinations was statistically significant (mean difference = 5.2 km/h; P = 0.045). It should be noted that the high value of 'VT-C for the critical sag combinations could be due to the longitudinal grade at midpoint of the curve (in this point the road is uphill). However the values of longitudinal grade are low (1.5% and 2.9%) and, in accordance with the literature (e.g. TRB, 2011), they do not lead to any appreciable conditioning of drivers’ speeds. This is also supported by the result that was obtained on VT: the mean value of VT was not significantly different for the 3 longitudinal grades of the approach tangent (0%, 2% and 4%; see table 1). Hence, the reduction in speed on the critical sag combinations it is deemed to be due exclusively to the configuration of the combined curves. 4. Discussion and conclusions The data analysis showed: x the same driver’s speed behavior on reference curves and suggested sag combinations (VT and 'VT-C did not differ statistically significant for the 2 types of curve); x a different driver’s speed behavior on critical sag combinations and on suggested sag combinations (VT did not differ statistically significant and 'VT-C on the critical sag combinations was significantly higher - + 5.2 km/h than the value on suggested sag combinations). Similar result was obtained from the comparison of the driver’s speed behavior on critical sag combinations and reference curves. However in this case the difference of 'VT-C was not statistically significant, although the value (+4.9 km/h) was practically the same of that recorded between the critical sag combinations and suggested sag combinations (+5.2 km/h). The first result does not support the hypothesis according to which on the sag combinations, because the horizontal radius is deemed to be perceived as being greater than it actually is, the driver adopts a significantly less reduction of speed between the approach tangent and the curve than that on reference curves. The result is consistent with a previous study carried out at CRISS driving simulator (Bella, 2014) which did not confirm the perception hypothesis for the sag combinations, and it is in line with the findings of Hassan and Sarhan (2012), who found slight differences in drivers’ responses on sag combinations and on flat horizontal curves.
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
The obtained results confirm the effectiveness of the road design guidelines for the coordination of horizontal curves and sag vertical curves. The suggested sag combination do not determine an anomalous driver’s speed behavior, whereas the critical sag combination causes a high reduction in speed along the tangent- curve transition, which points the driver’s reaction to the wrong perception of the road alignment. It should be noted that such suggestions come from studies based on the drawing of the perspective of the road and are not based on the analysis of the driver’s speed behavior induced by the driver’s perception of the road while driving. Consequently the findings of the present driving simulator study, that are based on the analysis of the driver’s speed behavior induced by the road configurations, provide an additional and even more reliable validation of the guideline indications for the coordination of the sag combinations. Finally, it should be noted that the speeds on the reference curves and sag combinations, although being fully consistent with those obtained in previous studies on driver’s speed behaviour on combined curves carried out using driving simulators (Garcia et al. 2011; Hassan and Sarhan, 2012), are high in comparison with those that are usually recorded for free vehicles on real two-lane rural roads. However for the purposes of the study, absolute validity is not essential and it is necessary only to have the relative validity according to Tornos (1998), since the research is dealing with matters relating to the effects of independent variables and is not aimed at determining absolute numerical measurements of the driver behavior. It must also be noted that the relative validity of the CRISS driving simulator for speed research analysis on two-lane rural roads similar to those used in this research was previously proven (Bella, 2008b). For these reasons, sufficient guarantees are provided concerning the validity of the methodological approach used in the present study. The findings of this study are valid only as regards the configurations of combined curves which have been studied. Further research should be aimed at enlarging the sample of curves in terms of longitudinal grade of the approach tangent and departure tangent as well as horizontal radius. Acknowledgements The research has been developed with the financial support of the Italian Ministry for University and Scientific Research. References American Association of State Highway Transportation Officials AASHTO, 2011. Green Book: A Policy on geometric design of highways and streets. 6th Edition. Washington D.C . Auberlet, J.-M., Pacaux, M.-P., Anceaux, F., Plainchault, P., Rosey, F., 2010. The impact of perceptual treatments on lateral control: a study using fixed-base and motion-base driving simulators. Accident Analysis and Prevention 42, 166–173. Auberlet, J.-M, Rosey, F., Anceaux, F., Aubind S., Briand P., Pacaux, M.-P., Plainchault, P., 2012.The impact of perceptual treatments on driver’s behavior: From driving simulator studies to field tests—First results. Accident Analysis and Prevention 45, 91-98. Bella, F., 2007. Parameters for evaluation of speed differential: contribution using driving simulator. Transportation Research Record: Journal of the Transportation Research Board, 2023, 37–43. doi: 10.3141/2023-05 Bella, F., 2008a. New model to estimate speed differential in tangent-curve transition. Advances in Transportation Studies an international Journal, 15, 27–36. doi: 10.4399/97888548186823 Bella, F., 2008b. Driving simulator for speed research on two-lane rural roads. Accident Analysis and Prevention 40, 1078–1087. doi: 10.1016/j.aap.2007.10.015 Bella, F., 2009. Can the driving simulators contribute to solving the critical issues in geometric design? Transportation Research Record: Journal of the Transportation Research Board, 2138, 120–126. doi: 10.3141/2138-16 Bella, F., 2011. How traffic conditions affect driver behavior in passing maneuver. Advances in Transportation Studies an international Journal, Special Issue, 113–126. doi: 10.4399/978885484657911 Bella, F. 2013. Driver perception of roadside configurations on two-lane rural roads: Effects on speed and lateral placement. Accident Analysis and Prevention, 50, 251-262. doi: 10.1016/j.aap.2012.04.015 Bella, F., 2014. Driver perception hypothesis: Driving simulator study. Transportation Research Part F, 24, 183–196 doi: 10.1016/j.trf.2014.04.007 Bella, F., 2014b. Driver performance approaching and departing curves: driving simulator study. Traffic Injury Prevention, 15, 310–318. doi: 10.1080/15389588.2013.813022 Bella, F., 2014c. Operating speeds from driving simulator tests for road safety evaluation. Journal of Transportation Safety & Security, 6 (03), 220–234. doi: 10.1080/19439962.2013.856984
107
108
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
Bella, F., Calvi, A., 2013. Effects of Simulated Day and Night Driving on the Speed Differential in Tangent–Curve Transition: A Pilot Study Using Driving Simulator. Traffic Injury Prevention, 14 (4), 413–423. doi: 10.1080/15389588.2012.716880 Bella, F, D’Agostini, G., 2010. Combined effect of traffic and geometrics on rear-end collision risk: a driving simulator study. Transportation Research Record: Journal of the Transportation Research Board, 2165, 96–103. doi: 10.3141/2165-11 Bella, F, Russo, R., 2011. A collision warning system for rear-end collision: a driving simulator study. Procedia – Social and Behavioral Sciences, Vol. 20, 676–686. doi:10.1016/j.sbspro.2011.08.075 Bidulka, S., Sayed, T., Hassan, Y., 2002. Influence of Vertical Alignment on Horizontal Curve Perception : Phase I Examining the Hypothesis. In Transportation Research Record: Journal of the Transportation Research Board, 1796, 12-23 Cartes, O., 2002. Multiple Perspectives. In Fuller R., Santos J.A. (Eds), Human Factors for Highway Engineers,11-21. Elsevier Science Ltd. Easa, S.M., Ganguly, C., 2005. Modeling Driver Visual Demand on Complex Horizontal Alignments. Journal of Transportation Engineering, Vol. 131, No. 8, 583–590; Easa, S.M., He, W., 2006. Modeling Driver Visual Demand on Three-Dimensional Highway Alignments. Journal of Transportation Engineering, Vol. 132, No. 5, 357-365 Fitzpatrick, K., Elefteriadou, L., Harwood, D.W., Collins, J.M., McFadden, J., Anderson, I.B., 2000. Speed Prediction for Two-Lane Rural Highways. McLean, VA: Federal Highway Administration; Report No. FHWA-RD-99–171. Garcia, A., Tarko, A., Dols Ruíz, J. F., Moreno Chou, A. T., Calatayud, D., 2011. Analysis of the influence of 3D coordination on the perception of horizontal curvature using driving simulator. Advances in Transportation Studies an international Journal, 24, 33-44 Hassan, Y., Sayed, T., 2002. Use of Computer animation in quantifying driver perception of three-dimensional road alignments. In Proc. International Conference Application of advanced technology in transportation. ASCE, Boston, 877- 884 Hassan, Y., Sayed, T., Bidulka, S., 2002. Influence of Vertical Alignment on Horizontal Curve Percepition : Phase II Modeling perceived Radius. In Transportation Research Record: Journal of the Transportation Research Board, No.1796, TRB, National Research Council, Washington, D.C., pp 24-34 Hassan, Y., Easa, S. M., 2003. Effect of vertical on driver perception of horizontal curves. In Journal Transportation Engineering, july/august, ASCE Boston, 399-407 Hassan, Y., 2004. Three-dimensional approach for roadway alignment design incorporating driver perception. In Advances in Transportation Studies, 2, Aracne Rome, 15-32 Hassan, Y., Sarhan, M., 2012. Operational Effects of Drivers’ Misperception of Horizontal Curvature. Journal of Transportation Engineering, Vol. 138, No. 11, 1314-1320 Lamm, R., Choueiri, E.M., Hayward, J.C., Paluri, A., 1988. Possible Design procedure to promote design consistency in highway geometric design on two-lane rural roads. In Transportation Research Record: Journal of the Transportation Research Board, No 1195, TRB, National Research Council, Washington, D.C., 111-122. Lamm, R., Psarianos, B., Mailaender, T., 1999. Highway Design and Traffic Safety Engineering Handbook. McGraw-Hill, New York Misaghi, P., Hassan, Y., 2005. Modeling operating speed and speed differential on two-lane rural roads. In Journal Transportation Engineering, ASCE, June 2005, 408-417 Mori, Y., Kurihara, M., Hayama, A., Ohkuma, S., 1995. A study to improbe the safety of expressways by desirable combinations of geometric alignments. In Proc. 1st International. Symposium On Highway Geometric Design Practices, Washington, D.C. Ministry of Infrastructures and Transports, 2001. Functional and geometrical guidelines for road construction M.D. November 5th, 2001. (in Italian) Ministerio de Fomento, 2001. Direccion General de Carreteras. Istruccion de carreteras: Norm 3.1 –IC, Trazado. Madrid, (in Spanish) National Highway Traffic Safety Administration, 2011. Fatality Reporting Analysis System, Available at: http://www-fars.nhtsa.dot.gov/Main/index.aspx Rosey, F., Auberlet, J-M., Bertrand, J., Plainchault, P., 2008. Impact of perceptual treatments on lateral control during driving on crest vertical curves: a driving simulator study. Accident Analysis and Prevention 40, 1513–1523. Smith, B.L., Lamm, R., 1994. Coordination of Horizontal and vertical alignment with regard to highway esthetics. Transportation Research Record Journal of the Transportation Research Board, 1445, 73-85 Tornos, J., 1998. Driving behaviour in a real and a simulated road-tunnel: a validation study. Accident Analysis and Prevention 30 (4), 497–503 TRB - Transportation Research Board, 2011. Transportation Research Circular E-C151: Modeling Operating Speed. Synthesis Report. Transportation Research Board 500 Fifth Street, NW Washington DC. Wooldridge, M., D., Fitzpatrick, K., Koppa, R., Bauer, K., 2000. Effects of horizontal curvature on driver visual demand. In Transportation Research Record: Journal of the Transportation Research Board, 1737, 71-77
ScienceDirect Transportation Research Procedia 3 (2014) 100 – 108
17th Meeting of the EURO Working Group on Transportation, EWGT2014, 2-4 July 2014, Sevilla, Spain
Effects of combined curves on driver’s speed behavior: driving simulator study Francesco Bella * Roma TRE University - Department of Engineering, via Vito Volterra n. 62 - 00146 Rome, Italy
Abstract The probability to occur in drive perception errors increases as the complexity of the road alignment increases. In particular perceptions errors could be significantly relevant in the conditions of horizontal curves overlapped with sag vertical curves (sag combinations or combined curves). The highway geometric design guidelines of several Countries provide suggestions for the coordination of the sag combinations in order to avoid combined configurations which can bring to undesirable optical effects and a reduced safety. Such suggestions come from studies based on the drawing of the perspective of the road. This drawing method is heavily limited with regards to the simulation of the perspective view of the highway to the driver during the dynamic task of the driving. Interactive driving simulation methods are deemed to be more efficient for these aims. This paper reports the results of a study carried out using an interactive driving simulator and aimed at evaluating the effects on the driver’s speed behavior of different configurations of sag combinations and non-combined curves on flat grade with the same features as the horizontal curves of the sag combinations (reference curves). The main result was that on suggested sag combinations the driver’s speed behavior did not differ in any statistically significant way from that on the reference curves. Whereas the critical sag combinations (configurations that should be avoided) caused a high reduction in speed along the tangent–curve transition, which pointed the driver’s reaction to the wrong perception of the road alignment This result, therefore, confirmed the effectiveness of the road design guidelines for the coordination of horizontal curves and sag vertical curves. © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license © 2014 The Authors. Published by Elsevier B. V. (http://creativecommons.org/licenses/by-nc-nd/3.0/). Committee of EWGT2014. Selectionand andpeer-review peer-review under responsibility the Scientific under responsibility of the of Scientific Committee of EWGT2014 Selection Keywords: driving simulator; road safety; driver behavior; combined curves
* Corresponding author. Tel.: +39-06-57.33.34.16; fax: +39-06-57.33.34.41 E-mail address: [email protected]
2352-1465 © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Scientific Committee of EWGT2014 doi:10.1016/j.trpro.2014.10.095
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
101
1. Introduction Curves are the geometric element of the road alignment characterised by the greater risk of accidents. According to the Fatality Analysis Reporting System (FARS), since 2005, about 5000 fatalities each year have resulted from single-vehicle run-off-road crashes on the horizontal curve sections of 2-lane rural roads in the United States (National Highway Traffic Safety Administration, 2011). Such statistics are deemed to be due to the erroneous perception of the features of the alignment that induces drivers to assume an inadequate behavior compared to the geometric design of the curved section (Cartes, 2002). Several researches have pointed out that the occurrence of erroneous perception increases as the complexity of the alignment increases and that erroneous perception could be significantly relevant in the conditions of horizontal curves overlapping with sag vertical curves or with crest vertical curves (Smith and Lamm, 1994; Mori et al., 1995; Wooldridge et al., 2000; Bidulka et al., 2002). In particular Smith and Lamm (1994) hypothesized that an overlapping crest curve may cause the horizontal curve to look sharper while a sag curve may cause the horizontal curve to look flatter than it actually is (called driver perception hypothesis). Then the driver may adopt a lower or higher speed, respectively, than if the radius were on a flat grade. Therefore the erroneous perception of the horizontal curve may be particularly hazardous for the horizontal curve overlapping with sag vertical curve (called combined curve or sag combination) where the drivers may perceive a sharp curve as a flat one. The road design guidelines of several Countries (e.g. Italy, Spain, USA) (Ministry of Infrastructures and Transports, 2001; Ministerio de Fomento, 2001; AASHTO, 2011), as a priority, invite to avoid the overlapping of horizontal and sag vertical curves and, if not possible, they affirm the need to overlap the vertices and to design vertical and horizontal curves with lengths of the same order of magnitude (here called suggested sag combination). In addition, the guidelines suggest to avoid sag combination formed by horizontal curve just after the end of the sag vertical curve, because this configuration (here called critical sag combination) causes important undesirable optical effects. These suggestions come from studies based on the drawing of the perspective of the road. This drawing method is deemed to be heavily limited, because it does not allow to simulate the perspective view of the road to the driver during the dynamic task of the driving. Therefore, in the last decade, numerous studies on the visual perception of the road were carried out by mean of the most advanced computer animation techniques (Bidulka et al., 2002; Hassan and Sayed, 2002; Hassan et al., 2002; Hassan and Easa, 2003; Hassan, 2004). However, such visualization techniques are non-interactive and do not allow to evaluate the driver’s reaction to its perception of the road scenario. The driving simulation is deemed to be the most accurate method in order to study the drivers perception (e.g. Lamm et al., 1999; Bella, 2009). Driving simulators offer several advantages such as low costs entailed in carrying out experiments, easy data collection, the utmost safety for test drivers, the possibility of carrying out experiments in controlled conditions. Besides such important benefits, driving simulators are interactive. They allow the test driver to manipulate the pedals and steering wheel of the vehicle during the task of driving and allow the recording of the effects of the road configurations on driver behavior in terms of speeds, trajectory, braking, and the like. Such features are the reason for the growing use of driving simulators for modeling driver visual demand on threedimensional highway alignments (Easa and Ganguly, 2005; Easa and He, 2006), for testing the effectiveness of road treatments on rural roads with crest vertical curves (Rosey et al., 2008; Auberlet et al., 2010; Auberlet et al., 2012) as well as for evaluating the effect of the interaction between overlapping horizontal and vertical alignments (Garcia et al., 2011; Hassan and Sarhan, 2012; Bella, 2014). The experimental study at the driving simulator reported here was carried out in order to provide an additional and even more reliable validation of the guideline indications for the coordination of horizontal curves overlapping with sag vertical curves. More specifically the aim of the study was to asses if such suggestions are able to determine: x on the suggested sag combinations, a driver’s speed behaviour that is not significantly different from that on the non-combined curves on flat grade with the same features as the horizontal curves of the sag combinations (called reference curve); x on the critical sag combinations, a driver’s speed behaviour that is significantly different (more critical for the road safety) from that on the suggested sag combinations.
102
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
For this purpose, the driver’s speed behaviour of each driver along the tangent-curve transition was recorded. More specifically, the difference in speed between the point on the approach tangent located 200 m from the beginning of the horizontal curve and the midpoint of the curve was analyzed. This because, according the literature (e.g. Lamm et al. 1988; Misaghi and Hassan, 2005; Bella, 2007; Bella 2008a), the speed reduction between successive locations of the road alignment increases as the driver detects undesirable optical effects or unclear and non-timely information provided by the road. 2. Method A within-subjects design was carried out using the fixed-base driving simulator of the Inter-University Research Centre for Road Safety (CRISS). On the basis of the speed data collected on the tangent-curve transitions of reference curves and sag combinations, one-way repeated MANOVA was performed to evaluate if the driver’s speed behavior on the horizontal curves was influenced by the type of curve (i.e. different configurations of sag combinations and reference curves). It should be noted that driving simulators do have one important limit. Drivers do not perceive any risk in a driving simulator. The driver’s awareness of being immersed in a simulated environment might give rise to a behavior which is different than that on a real road. However, several simulator validation studies have afforded us sufficient guarantees as regards the relative validity, which refers to the correspondence between effects of different variations in the driving situation. Absolute validity, which refers to the numerical correspondence between behavior in the driving simulator and in the real world, is not essential, whenever the research is dealing with matters relating to the effects of independent variables (Tornos, 1998). For the purpose of the present study, only relative validity is required and the CRISS driving simulator has been previously validated as a useful tool for studying driver’s speed behavior on two-lane rural roads (Bella, 2008b). This evidence has also allowed us to successfully use the CRISS driving simulator for studying the driver behavior induced by road configurations as well as for providing insights that may help to guide road design of two-lane rural roads (e.g. Bella, 2011; Bella, 2013; Bella, 2014b; Bella, 2014c; Bella and D’Agostini, 2010; Bella and Russo, 2011; Bella and Calvi, 2013). 2.1. Road scenarios, sag combinations and reference curves Two two-lane rural roads, about 15 km long, were designed. The cross-section was 10.50m wide, formed by two 3.75m wide lanes and two 1.50m wide shoulders. The values of the circular curves’ radius ranged from 118m to 800m. The length of tangents ranged from 150m to 2200m, while the deflection angle of horizontal curves ranged from 30° to 80°. The longitudinal grades were not over 6%. Italian guidelines assume for these roads a design speed ranged between 60 km/h (on curve with radius equal to 118m) and 100 km/h (on tangent). The posted speed limit is 90 km/h. These roads had the following types of sag combinations (fig. 1): x suggested sag combination: the sag vertical curve is overlapped to horizontal curve so the vertices of the two curves coincided and their length was the same order of magnitude, as required by design guidelines for the coordination of horizontal alignment and profile (Ministry of Infrastructures and Transports, 2001); x critical sag combination: the horizontal curve begins just after the end of the sag vertical curve. The their length was the same order of magnitude. The guidelines (Ministry of Infrastructures and Transports, 2001) suggest to avoid this configuration because it causes anomalies of the perspective of the road alignment. Such sag combinations and reference curves (non-combined curves on flat grade with the same features as the horizontal curves of the sag combinations) were the curves of interest. Half of these curves were on the first road and the other half was on the second alignment. This in order to: x limit the order effect induced by the same sequence of presentation of the curves to the driver (the two road scenarios were driven by drivers in a counterbalanced order); x limit the duration of tests in the driving simulator and consequently limit the potential effects of fatigue on the driver (see also the next section Procedure and participants).
103
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
The geometric parameters of the curves are shown in table 1, while figure 1 shows the configurations of the two types of sag combination. Table 1. The Geometric features of the references curves and sag combinations Horizontal curve Lcirc La.t.
J
Rv
Lv
ia
id
'i
400
400
77°
-
-
0
0
0
800
800
65°
-
-
0
0
0
200
400
400
77°
11430
400
-2.0
1.5
3.5
180
300
800
800
65°
9566
660
-4.0
2.9
6.9
140
200
400
400
77°
11430
400
-2.0
1.5
3.5
180
300
800
800
65°
9566
660
-4.0
2.9
6.9
Lc
Lcl
Reference curves
252
480
140
200
437
660
180
300
Suggested sag combinations
252
480
140
437
660
252
480
437
660
Critical sag combinations
Vertical curve Ld.t.
R
R = radius of horizontal curve
J = deflection angle
Lc = length of horizontal curve in m
Rv = radius of vertical curve in m
(Lcl+Lcirc+Lcl)
Lv = length of vertical curve in m ia = approach grade in percent
Lcl = length of clothoids in m Lcirc = length of circular curve in m
id = departure grade in percent
L a.t. = length of approach tangent in m
'i=~id-ia~
L d.t. = length of departure tangent in m
Fig. 1. Configurations of sag combinations: suggested and critical
104
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
2.2. Apparatus The CRISS simulation system is an interactive fixed-base driving simulator. The system allows to represent the infrastructure scenario, traffic conditions, configurations of horizontal and vertical alignments, cross section features, and to simulate the friction between tires and road surface and the vehicle’s physical and mechanical characteristics. The hardware interfaces (wheel, pedals and gear lever) are installed on a real vehicle. The driving scene is projected onto three screens; one in front of the vehicle and two on each side. The usual field of view is 135°. The scenario is updated dynamically according to the travelling conditions of the vehicle, depending on the actions of the driver on the pedals and the steering wheel. The resolution of the visual scene is 1024x768 pixel and the update rate is 30-60 Hz depending on scene complexity. The system is also equipped with a sound system that reproduces the sounds of the engine. This setup provides a realistic view of the road and surrounding environment. The system allows the intensity of driver actions on the brake, accelerator pedal, and steering wheel to be recorded and provides many parameters to describe travel conditions (e.g., vehicle barycenter, relative position in relation to the road axis, local speed and acceleration, steering wheel rotation angle, pitching angle, rolling angle). All the data can be recorded at time or space intervals of a fraction of a second or a fraction of a meter. Figure 2 shows an example of the road scenario as seen by the driver during the driving simulation. 2.3. Procedure and participants The experiment was carried out using dry pavement conditions in good state of maintenance and with the free vehicle on its own driving lane. Whereas, on the driving lane a modest traffic was distributed randomly for the sole purpose of inducing the driver not to invade it. The vehicles in the opposite lane were always present in those sections set away from the curves of interest. The simulated vehicle was a standard medium class car, both for dimension and for mechanical performance, with an automatic gear. The data recording system acquired all the parameters at spatial intervals of 5 m. The driving procedure was broken down into the following steps: (a) communicate to the driver about the duration of the driving and the use of the steering wheel, pedals, and automatic gear; (b) train as to how to use the driving simulator on a specific alignment for approximately 10 min to allow the driver to become familiar with the simulator’s control instruments; (c) execute the first test scenario; (d) have the driver vacate the car for about 5 min so as to reestablish a psychophysical state similar to the one at test start and to fill out a form with personal data (e.g., years of driving experience, average annual distance driven); (e) execute the second test scenario; and (f) have driver answer a questionnaire as to any discomfort perceived during the driving procedure, including the type (e.g. nausea, giddiness, daze, fatigue, other) and the intensity (e.g. null, light, medium, high). Participants were instructed to drive as they normally would in the real world. Thirty-five drivers were selected to perform the driving in the simulator according to the following characteristics: no experience with the driving simulator, at least four years of driving experience and an average annual driven distance on rural roads of at least 2500 km.
Fig. 2. Driving phase from the simulator
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
105
The participants, male (63%) and female (37%), ranged from 23 to 60 years of age (average 26). From the analysis of the questionnaire filled in by the drivers at the end of the test, it emerged that no participants experienced any discomfort condition. No participant therefore was excluded from the sample. The sequence of the two scenarios was varied for each driver, so as to avoid any influences that might result from the repetition of the experimental conditions in the same order. The participants completed the procedure in less than 60 minutes. 2.4. Data collection For each sag combination and reference curve, the speeds of the drivers were recorded along the section formed by the last 200 m of the approach tangent and the horizontal curve. More specifically, the following local speeds of each driver were collected (fig 3): x speed (VT) at the point (T) on the approach tangent located 200 m from the beginning of the horizontal curve; x speed (VC) at the midpoint (C) of the horizontal curve; x the difference of speed ('VT-C) between VT and VC. VT was analyzed in order to ascertain whether or not, driver’s speed at point T, was unaffected by the type of the successive curve. It should be noted that the choice of this point is consistent with the results of Fitzpatrick et al. (2000) who found that the speed along the approach tangent does not begin to drop until at a point closer than 200 m to the point of curvature. Should it be confirmed, as expected, that VT does not depend on the type of curve, the possible difference between the values of VC and 'VT-C on the different successive curves (sag combinations and reference curves) shall exclusively depend on the conditioning induced by the type of curve. VC and 'VT-C were analyzed to ascertain if the drivers’ speed behavior on the section of tangent-curve transition was affected by the type of the curve. 3. Data analysis and results In order to evaluate the effects on the driver’s speed behaviour induced by the 2 types of sag combination and reference curves, a repeated measures MANOVA was performed. More specifically, one-way repeated measures MANOVA was carried out in order to investigate the effects on the two dependent variables (VT and 'VT-C) due to the independent variable (or factor) type of curve (3 types: reference, and 2 types of sag combination: suggested and critical). It should be noted that VC was not used as dependent measure in MANOVA test in order to avoid redundancy in the dependent variables. Figure 4 shows the mean values of the dependent measures VTand'VT-C and their 95% confidence intervals for every type of curve. The VC values are also shown. The MANOVA revealed a significant effect for type of curve (F(6,272) = 14.616, P = 0.000). Univariate statistics (Mauchly’s test revealed that the assumption of sphericity was ascertained for VT, while for 'VT-C a Greenhouse– Geisser correction was used) showed that the type of curve did not affect the dependent measure VT (F(1.749, 120.710) = 1.886, P = 0.161), while it significantly affected the dependent measure 'VT-C (F(2, 138) = 3.811, P= 0.024).
Fig. 3. Locations where speed data were collected
106
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
Fig. 4. Mean values of VT, VC and'VT-C for reference curves and sag combinations (bounds of 95% confidence interval are also shown)
Hence, having ascertained that VT is not affected by the driver’s perception of the type of curve, it is possible to affirm that the difference between the values of 'VT-C depends entirely on the conditioning induced by the type of curve. Post hoc tests using the Bonferroni correction revealed that the mean value of 'VT-C (17.1 km/h) on reference curves was not significantly different than that (16.8 km/h) on suggested sag combinations (mean difference= 0.3km/h; P= 1.000). The mean value of 'VT-C on reference curves (17.1 km/h) was less than the mean value (22.0 km/h) on critical sag combinations, however the difference was not statistically significant (mean difference = 4.9 km/h; P = 0.125). The difference between the mean value of 'VT-C on suggested sag combinations and that on critical sag combinations was statistically significant (mean difference = 5.2 km/h; P = 0.045). It should be noted that the high value of 'VT-C for the critical sag combinations could be due to the longitudinal grade at midpoint of the curve (in this point the road is uphill). However the values of longitudinal grade are low (1.5% and 2.9%) and, in accordance with the literature (e.g. TRB, 2011), they do not lead to any appreciable conditioning of drivers’ speeds. This is also supported by the result that was obtained on VT: the mean value of VT was not significantly different for the 3 longitudinal grades of the approach tangent (0%, 2% and 4%; see table 1). Hence, the reduction in speed on the critical sag combinations it is deemed to be due exclusively to the configuration of the combined curves. 4. Discussion and conclusions The data analysis showed: x the same driver’s speed behavior on reference curves and suggested sag combinations (VT and 'VT-C did not differ statistically significant for the 2 types of curve); x a different driver’s speed behavior on critical sag combinations and on suggested sag combinations (VT did not differ statistically significant and 'VT-C on the critical sag combinations was significantly higher - + 5.2 km/h than the value on suggested sag combinations). Similar result was obtained from the comparison of the driver’s speed behavior on critical sag combinations and reference curves. However in this case the difference of 'VT-C was not statistically significant, although the value (+4.9 km/h) was practically the same of that recorded between the critical sag combinations and suggested sag combinations (+5.2 km/h). The first result does not support the hypothesis according to which on the sag combinations, because the horizontal radius is deemed to be perceived as being greater than it actually is, the driver adopts a significantly less reduction of speed between the approach tangent and the curve than that on reference curves. The result is consistent with a previous study carried out at CRISS driving simulator (Bella, 2014) which did not confirm the perception hypothesis for the sag combinations, and it is in line with the findings of Hassan and Sarhan (2012), who found slight differences in drivers’ responses on sag combinations and on flat horizontal curves.
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
The obtained results confirm the effectiveness of the road design guidelines for the coordination of horizontal curves and sag vertical curves. The suggested sag combination do not determine an anomalous driver’s speed behavior, whereas the critical sag combination causes a high reduction in speed along the tangent- curve transition, which points the driver’s reaction to the wrong perception of the road alignment. It should be noted that such suggestions come from studies based on the drawing of the perspective of the road and are not based on the analysis of the driver’s speed behavior induced by the driver’s perception of the road while driving. Consequently the findings of the present driving simulator study, that are based on the analysis of the driver’s speed behavior induced by the road configurations, provide an additional and even more reliable validation of the guideline indications for the coordination of the sag combinations. Finally, it should be noted that the speeds on the reference curves and sag combinations, although being fully consistent with those obtained in previous studies on driver’s speed behaviour on combined curves carried out using driving simulators (Garcia et al. 2011; Hassan and Sarhan, 2012), are high in comparison with those that are usually recorded for free vehicles on real two-lane rural roads. However for the purposes of the study, absolute validity is not essential and it is necessary only to have the relative validity according to Tornos (1998), since the research is dealing with matters relating to the effects of independent variables and is not aimed at determining absolute numerical measurements of the driver behavior. It must also be noted that the relative validity of the CRISS driving simulator for speed research analysis on two-lane rural roads similar to those used in this research was previously proven (Bella, 2008b). For these reasons, sufficient guarantees are provided concerning the validity of the methodological approach used in the present study. The findings of this study are valid only as regards the configurations of combined curves which have been studied. Further research should be aimed at enlarging the sample of curves in terms of longitudinal grade of the approach tangent and departure tangent as well as horizontal radius. Acknowledgements The research has been developed with the financial support of the Italian Ministry for University and Scientific Research. References American Association of State Highway Transportation Officials AASHTO, 2011. Green Book: A Policy on geometric design of highways and streets. 6th Edition. Washington D.C . Auberlet, J.-M., Pacaux, M.-P., Anceaux, F., Plainchault, P., Rosey, F., 2010. The impact of perceptual treatments on lateral control: a study using fixed-base and motion-base driving simulators. Accident Analysis and Prevention 42, 166–173. Auberlet, J.-M, Rosey, F., Anceaux, F., Aubind S., Briand P., Pacaux, M.-P., Plainchault, P., 2012.The impact of perceptual treatments on driver’s behavior: From driving simulator studies to field tests—First results. Accident Analysis and Prevention 45, 91-98. Bella, F., 2007. Parameters for evaluation of speed differential: contribution using driving simulator. Transportation Research Record: Journal of the Transportation Research Board, 2023, 37–43. doi: 10.3141/2023-05 Bella, F., 2008a. New model to estimate speed differential in tangent-curve transition. Advances in Transportation Studies an international Journal, 15, 27–36. doi: 10.4399/97888548186823 Bella, F., 2008b. Driving simulator for speed research on two-lane rural roads. Accident Analysis and Prevention 40, 1078–1087. doi: 10.1016/j.aap.2007.10.015 Bella, F., 2009. Can the driving simulators contribute to solving the critical issues in geometric design? Transportation Research Record: Journal of the Transportation Research Board, 2138, 120–126. doi: 10.3141/2138-16 Bella, F., 2011. How traffic conditions affect driver behavior in passing maneuver. Advances in Transportation Studies an international Journal, Special Issue, 113–126. doi: 10.4399/978885484657911 Bella, F. 2013. Driver perception of roadside configurations on two-lane rural roads: Effects on speed and lateral placement. Accident Analysis and Prevention, 50, 251-262. doi: 10.1016/j.aap.2012.04.015 Bella, F., 2014. Driver perception hypothesis: Driving simulator study. Transportation Research Part F, 24, 183–196 doi: 10.1016/j.trf.2014.04.007 Bella, F., 2014b. Driver performance approaching and departing curves: driving simulator study. Traffic Injury Prevention, 15, 310–318. doi: 10.1080/15389588.2013.813022 Bella, F., 2014c. Operating speeds from driving simulator tests for road safety evaluation. Journal of Transportation Safety & Security, 6 (03), 220–234. doi: 10.1080/19439962.2013.856984
107
108
Francesco Bella / Transportation Research Procedia 3 (2014) 100 – 108
Bella, F., Calvi, A., 2013. Effects of Simulated Day and Night Driving on the Speed Differential in Tangent–Curve Transition: A Pilot Study Using Driving Simulator. Traffic Injury Prevention, 14 (4), 413–423. doi: 10.1080/15389588.2012.716880 Bella, F, D’Agostini, G., 2010. Combined effect of traffic and geometrics on rear-end collision risk: a driving simulator study. Transportation Research Record: Journal of the Transportation Research Board, 2165, 96–103. doi: 10.3141/2165-11 Bella, F, Russo, R., 2011. A collision warning system for rear-end collision: a driving simulator study. Procedia – Social and Behavioral Sciences, Vol. 20, 676–686. doi:10.1016/j.sbspro.2011.08.075 Bidulka, S., Sayed, T., Hassan, Y., 2002. Influence of Vertical Alignment on Horizontal Curve Perception : Phase I Examining the Hypothesis. In Transportation Research Record: Journal of the Transportation Research Board, 1796, 12-23 Cartes, O., 2002. Multiple Perspectives. In Fuller R., Santos J.A. (Eds), Human Factors for Highway Engineers,11-21. Elsevier Science Ltd. Easa, S.M., Ganguly, C., 2005. Modeling Driver Visual Demand on Complex Horizontal Alignments. Journal of Transportation Engineering, Vol. 131, No. 8, 583–590; Easa, S.M., He, W., 2006. Modeling Driver Visual Demand on Three-Dimensional Highway Alignments. Journal of Transportation Engineering, Vol. 132, No. 5, 357-365 Fitzpatrick, K., Elefteriadou, L., Harwood, D.W., Collins, J.M., McFadden, J., Anderson, I.B., 2000. Speed Prediction for Two-Lane Rural Highways. McLean, VA: Federal Highway Administration; Report No. FHWA-RD-99–171. Garcia, A., Tarko, A., Dols Ruíz, J. F., Moreno Chou, A. T., Calatayud, D., 2011. Analysis of the influence of 3D coordination on the perception of horizontal curvature using driving simulator. Advances in Transportation Studies an international Journal, 24, 33-44 Hassan, Y., Sayed, T., 2002. Use of Computer animation in quantifying driver perception of three-dimensional road alignments. In Proc. International Conference Application of advanced technology in transportation. ASCE, Boston, 877- 884 Hassan, Y., Sayed, T., Bidulka, S., 2002. Influence of Vertical Alignment on Horizontal Curve Percepition : Phase II Modeling perceived Radius. In Transportation Research Record: Journal of the Transportation Research Board, No.1796, TRB, National Research Council, Washington, D.C., pp 24-34 Hassan, Y., Easa, S. M., 2003. Effect of vertical on driver perception of horizontal curves. In Journal Transportation Engineering, july/august, ASCE Boston, 399-407 Hassan, Y., 2004. Three-dimensional approach for roadway alignment design incorporating driver perception. In Advances in Transportation Studies, 2, Aracne Rome, 15-32 Hassan, Y., Sarhan, M., 2012. Operational Effects of Drivers’ Misperception of Horizontal Curvature. Journal of Transportation Engineering, Vol. 138, No. 11, 1314-1320 Lamm, R., Choueiri, E.M., Hayward, J.C., Paluri, A., 1988. Possible Design procedure to promote design consistency in highway geometric design on two-lane rural roads. In Transportation Research Record: Journal of the Transportation Research Board, No 1195, TRB, National Research Council, Washington, D.C., 111-122. Lamm, R., Psarianos, B., Mailaender, T., 1999. Highway Design and Traffic Safety Engineering Handbook. McGraw-Hill, New York Misaghi, P., Hassan, Y., 2005. Modeling operating speed and speed differential on two-lane rural roads. In Journal Transportation Engineering, ASCE, June 2005, 408-417 Mori, Y., Kurihara, M., Hayama, A., Ohkuma, S., 1995. A study to improbe the safety of expressways by desirable combinations of geometric alignments. In Proc. 1st International. Symposium On Highway Geometric Design Practices, Washington, D.C. Ministry of Infrastructures and Transports, 2001. Functional and geometrical guidelines for road construction M.D. November 5th, 2001. (in Italian) Ministerio de Fomento, 2001. Direccion General de Carreteras. Istruccion de carreteras: Norm 3.1 –IC, Trazado. Madrid, (in Spanish) National Highway Traffic Safety Administration, 2011. Fatality Reporting Analysis System, Available at: http://www-fars.nhtsa.dot.gov/Main/index.aspx Rosey, F., Auberlet, J-M., Bertrand, J., Plainchault, P., 2008. Impact of perceptual treatments on lateral control during driving on crest vertical curves: a driving simulator study. Accident Analysis and Prevention 40, 1513–1523. Smith, B.L., Lamm, R., 1994. Coordination of Horizontal and vertical alignment with regard to highway esthetics. Transportation Research Record Journal of the Transportation Research Board, 1445, 73-85 Tornos, J., 1998. Driving behaviour in a real and a simulated road-tunnel: a validation study. Accident Analysis and Prevention 30 (4), 497–503 TRB - Transportation Research Board, 2011. Transportation Research Circular E-C151: Modeling Operating Speed. Synthesis Report. Transportation Research Board 500 Fifth Street, NW Washington DC. Wooldridge, M., D., Fitzpatrick, K., Koppa, R., Bauer, K., 2000. Effects of horizontal curvature on driver visual demand. In Transportation Research Record: Journal of the Transportation Research Board, 1737, 71-77