- Email: [email protected]
An Integrated Approach to Collective Route Guidance
Copyright © IFAC Transportation Systems Chania, Greece, 1997
AN INTEGRATED APPROACH TO COLLECTIVE ROUTE GUIDANCE Marcus Hoops Maria Tsavachidis
Institute afTraffic Engineering and Planning, Technical University afMunich (FGV TUM) Arcisstr. 21, 80333 Munich, Germany
Abstract: In Munich only limited re-routing strategies have so far been applied to the existing network control system. New control strategies considering the different 00flows of traffic demand and the possible set of route combinations for chosen destination areas are investigated in a feasibility study. Because only limited destination zones can be displayed by the existing variable direction signs new re-routing strategies have to be assessed in a simulation environment. An integrated approach for defining, simulating and evaluating new re-routing strategies is developed, using the network monitoring tool NEMO and the strategy simulation tool STRAMA Keywords: Traffic Control, Simulation, State Estimation, Evaluation, State Monitoring
was to facilitate an integrated traffic management. The architecture required for that is mainly based on a traffic information pool and strategy and service centre (TIP/SSC) linking various important subsystems. One of the main measures for urbanIinterurban control in Munich is a collective route guidance system at the fringe of the urban and motorway network to the north (Fig. 1).
1. BACKGROUND
Constant traffic increase and exhausted network capacities in conurbation areas have commonly led to intensified efforts in the development of new approaches to network control Munich like other major urban centres suffers from increasing traffic demand and its related environmental and economic impacts to a degree which can no longer be solely met by infrastructural measures, i.e. a continuous adaption of the network to new levels of demand. It is therefore sought to develop and apply new traffic control and management systems which can make demand comply with the existing network rather than vice versa.
Only limited re-routing strategies have so far been applied due to the lack of appropriate strategies and diverging interests of the responsible authorities. The main conflict in defining optimal re-routing recommendations for the VDS system lies in diverging interests of Munich's municipality and the Freestate of Bavaria being responsible for the urban and motorway network respectively. While the motorway authority supports the diversion of traffic from their network onto urban arterials to increase traffic flow on the motorways, the city of Munich generally objects to additional traffic being induced onto urban roads where it is assumed to add to traffic
The future development of a coherent traffic management system for the wider area of Munich will be based on work done in the LLAMD Munich COMFORT (COoperative Management FOr urban and Regional Transport) project (Munich COMFORT. Apart from applying and assessing a set of traffic control and management systems a main objective
1103
related problems, which moreover effect areas of higher population density. Despite this conflict of interest the insight into an obvious need for harmonised control strategies is reflected by joined participation of both authorities in research activities on the integration of urban and inter-urban control (i.e. TABASCO, EC DG XIII . Transport Telernatics Programme). Specific tools are required to optmuse traffic planning and strategy development reflecting the characteristics of traffic demand and traffic related impacts in compliance with urban and interurban policies.
fringe of the urban network. The value of the diversion is not only limited due to this critical merging at the intersection but also due to the alternative route being app. 60% longer than the normal route. The direction signs installed do not allow for a diversification of diverting traffic to Munich by city districts, as only Munich and some long distance destinations are displayed. Therefore for some destinations the alternative route is not suitable for providing any significant benefit. Recognising the need for new re-routing models, the Technical University of Munich has developed the alternate routing algorithm V ARIA based on dynamic OD-estimation (Sachse, 1995). V ARIA will be integrated with an incident detection tool implemented on a main urban arterial, for a field trial on urban integrated traffic control in the Munich COMFORT test area. Although being a first step into more sophisticated collective route guidance, a wider range of strategies has yet to be developed
3. AN INTEGRATED APPROACH TO ALTERNATE ROUTING
3. J Selection of alternative routes The objective of this study was to develop a sophisticated approach to collective route guidance for an extended Munich COMFORT test site in showing potentials of other alternative routes using both motorway and urban network. To minimise adverse impacts on the urban arterials new rerouting strategies taking into account more distinct destination areas than are currently displayed by the VDS are investigated. Thereby it is intended to obtain alternative routes that are better adapted to the given ODs in the network.
~ VoriObie Oire<:tton Siqn
Fig. 1. Munich: Re-routing Network
In conjunction with respective work currently being undertaken within the TABASCO project, new strategies for collective route guidance complying with both urban and interurban policies were developed for the study area comprising both motorways and urban arterials. A network monitoring tool NEMO (NEtwork Monitor) was used off-line for the iterative selection of re-routing strategies (Hoops, et al., 1997). To facilitate the envisaged strategy assessment and calculation of potential benefits of this integrated re-routing approach a concept for a simulation with NEMO was developed.
Especially for traffic bound for destinations that are not near the access point of the A9 motorway other alternative routes seem to be more obvious than the current one, which serves as reference route. This applies in particular to traffic destinations in the western, south-western and southern parts of Munich. The OD-Matrix of the motorway shows that about 45% of traffic at the interchange Neufahrn, being the first decision point for the re-routing of traffic, is bound for Munich. After leaving the motorway a total of 90% of this traffic is allocated to two main urban arterials which drivers could easily access through other alternative routes. About 20% of the total traffic coming from the North and bound for Munich are heading for western and south-western parts and app. 30% for central and southern parts of Munich. Although it must be assumed that a share of
2. CURRENT NETWORK CONTROL PRACTICE Currently in case of an incident or congestion on the normal motorway route A9 to Munich, traffic is being diverted by variable direction signs to the bypass motorway route. Traffic on the normal and alternative route meet again at an intersection on the
1104
this traffic already uses routes other than the motorway A9 there still lies significant potential for re-routing the remaining traffic onto better alternatives.
The best alternative route selected for destinations in the centre and south of Munich holds potential for a 5,5% reduction in travel time and 17% in travel distance whereas the second route requires similar travel time, due to much lower mean speed but travel distance is about 30% reduced compared to the conventional route (Fig. 3).
For the selection of best routes the network monitor NEMO was used working on the basis of historical data. Congestion on the A9 was simulated thus making the router select other 'best' routes in terms of minimum individual travel time derived from mean speed and route length.
Munich -
Central South
One destination point was chosen to represent destinations of West/ Southwest Munich and Munich Centre/South respectively. For the best alternative route detennined for destination area West/SouthWest (Fig. 2) a reduction of 29% in travel time and 28% in travel distance in comparison to the conventional re-routing strategy was calculated. The showed best route holds a 10% and 16% reduction in travel time and distance respectively.
-Re ••• 81
_ •• 82
,
Munich· \ West I South-West"
-RA •••
A1
... - A:2.
. . . .__\
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1175
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Fig. 3. Alternative routes destinations
1451 A1
1311
25365 81
central/southern
Both new routes incorporate the urban arterial Ingolstaedterstrasse whereas the conventional route runs fully on the motorway network. Within the DRIVE IT project LLAMD / Munich COMFORT and the follow up project T ABASeO the possible use of the Ingolstaedterstrasse for alternate routing strategies was examined (Sachse and Csallner, 1995). It became evident that capacity resources for additional re-routed traffic exist only during limited time periods, which is partly due to a poor performance of the urban traffic control. Therefore currently these periods of free capacity do mostly not coincide with congestion periods on the A9. In case of incidents though, traffic flow on the motorway is disturbed to a degree which could make the urban arterial preferable in terms of overall adverse impacts.
87
1Q26
for
F
FGV·TUM
Fig. 2. Alternative routes for south/south-western destinations Looking at the distance travelled on urban roads, the one included in the conventional route is not significantly shorter or even longer than the alternatives. Thus diverting traffic onto urban arterials can be beneficial not only in terms of a reduction in adverse impacts on the overall network but also specifically on the urban network itself.
Although only to be seen as a rough estimate, as no real time data e.g. for peak periods was used, the offline calculation facilitated the choice of appropriate alternative routes and gave a rough picture of the potentials to be expected.
1105
The selected routes fonn the basis for the integrated re-routing approach to be developed.
3.2 Strategic Approach To be operational, new strategies have to be highly distinct and specified in terms of decision criteria. This requires above all verification and strategy assessment taking into account differences of traffic situations over time of day. The prerequisite for both operation and simulation is the identification of destination shares. For simulation these are derived from an historical matrix and applied on the actual traffic volume at the decision interchange Neufahm. Relevant streams are respectively allocated to all possible combinations of alternative routes chosen, fonning the set of variable re-routing strategies. The latter have to be assessed in detail with regard to travel time, energy consumption and environmental impacts in the study area. Variable choice of route combinations mainly taking into account capacity on the urban arterials affected, opens a wider range of possibilities, as traffic can be allocated evenly on the network optimising network efficiency overall. 4. INVESTIGATION BASED ON SIMULATION
4.1.
Context
Due to political restrictions and lack of appropriate installation the new strategies were not applicable in a field trial. In order to be able to evaluate re-routing strategies under conditions nearest to reality a simulation study was chosen.
simulation model is the uncertainty of the traffic state prognosis for complex traffic networks. Assignment models on the other hand are less accurate in the description of vehicle movements, because no in-depth traffic flow model is used. Nevertheless flow propagation models are reliable in estimating the mean traffic state based on OD-flows and less demanding in calculation.
4.2
The models NEMO and STRAMA
The actual implementation of the online-version of the Network Monitor (NEMO) was developed in the LLAMDlMunich-Comfort project (Hoops, 1997). It's main objective is the description of the traffic state in urban and rural networks. It is supplied with dynamic traffic counts, to some extend with traffic states and with the state of signalised intersections by traffic information centres through the Strategy and Service Centre (SSC). NEMO establishes the context of the data locally collected in space and time for the whole test site and derives traffic related impacts, such as travel time, delay time, emissions and energy consumption. Through traffic models the traffic state in the network is estimated in terms of traffic volume, speed, travel time and proportion of "traffic volume to capacity". In addition, based on the estimated traffic state, environmental variables like carbon monoxide, nitrogen oxides etc. are estimated . All these variables can be described by NEMO on the level of classes but not in terms of exact numbers as the traffic information available is not sufficient for a network as complex as the one examined by NEMO.
A main benefit of the simulation study lay in its independence from technical constraints in the field, e.g. the restricted set of messages of the Variable Direction Signs limiting the possibilities for a distinction between destination zones in Munich (e.g. Munich-CBD and Munich-West). A shortcoming of simulation studies in general can be a lack of confidence of the tools being used. The quality of the used network monitoring tool (NEMO) though, was demonstrated in the framework of an evaluation within the Munich COMFORT project.
Network Monitor NEMO is using a traffic network model which was derived from a digital road map of a common supplier for the test site Munich, traffic models like traffic assignment. origin-destination estimator (Van Zuylen, 1981), a queuing model (Kimber-Hollis), a capacity estimator (specifically for intersections), a simple traffic flow model and impact models to estimate the impacts like emissions and energy consumption (Fig. 4.).
In general the monitoring of the traffic impacts is based on the available traffic data in the SSC. Gaps in data are closed by using historical information or by interpolation.
The software tools were used for a first comparative evaluation of different alternative routes based on the traffic situation on the relevant stretches of the network. Thereby traffic demand was modified in order to simulate different scenarios and to compare them to the reference case.
Data are collected from the regional traffic control centre and urban control centre. In the urban control centre traffic flow data (i. e. traffic volume, speed and occupancy), the state of the signalised intersections and the actual selected signal plan are
In general such an investigation based on simulation can be perfonned with a simulation tool like a time propagation model or an assignment tool, which is a flow propagation model. The problem of applying a
1106
available. Traffic data and the actual OD-matrix are provided by the regional traffic control centre. NEMO network elements are intersections and links. A queuing model for intersections and a simple traffic flow model (Akcelik, 1978). for the links are being used. In the urban area one link between two intersections is described by a speed-flow-relation. The focus in urban areas lies on the realistic description of the intersections. In the rural area those arcs are linked together with individual speedflow-relation to describe the traffic behaviour on long motorways. With this approach big networks can be modelled. The actual network for the in-depth modelling analysis is at present limited to the Munich-COMFORT test site. This means the motorway network north of Munich and an urban area of approximately 220 signalised intersections, which represents 20% of the whole city area.
demand) in order to evaluate for example new traffic scenarios. STRAMA is comparing the network state for the 'with' and 'without' case. Within the project Munich COMFORT STRAMA was developed to handle the modification of some variable of network supply like change in the number of lanes, turning restrictions, lane blocking and speed limits. NEMO Internal Interaction between the Models
Global Data Base tor NEMO
OD-Estlmatlon at single intersections
+
Trat!ic Network Description. Dynamic T rafIic Data-8ank, Oescriplion of complex inletSeClions SIgnalIsation Historical OD-Matrix
OD-Estimation in Networ1
For the assignment procedure trip matrices are necessary. Whereas for the regional area a dynamic matrix is provided by the control centre, there is none available for the urban area. Therefore a historical matrix of the city's planning department was used. This matrix is based on average daily traffic (AD1). To make use of this matrix in NEMO it has to be disaggregated into one hour time intervals. The derived matrices will be updated by online counts in the network and an OD-estirnator based on the Van Zuylen (1981) approach.
Capacity E.s1imation Queue Model Flow-Speed ModeII
~ AssIgnment Path Flow Opnmisation in the network
1
I:=!
Cost Function (Travel Time)
~
Best Route Search
I
Traffic State of the Network
~
Environmental Modells
Analysis
Fig. 4. Model elements of NEMO
As the regional and the urban network in the investigation area are connected, the matrices have to be linked with respect to some origins and destinations, i.e. those at the fringe of both networks. The one hour matrices are assigned to the network according to the volume and the derived costs on the individual links. Two methods are used for assignment, i.e. the incremental and the user equilibrium assignment. The best approach is selected during the test period of NEMO. Because of the unreliability of the urban OD-matrix the assignment procedure was extended with a path-flow optimisation, which tries to fit the path-flows with the traffic counts on the links.
Model Extension For investigating the alternative routing strategies some extensions of the NEMO and STRAMA tools were necessary. For carrying out an off-line investigation it appeared to be necessary to emulate first the base framework, i.e. a congestion on the A9 between the intersections Neufahrn and MunichNorth. This is realised by introducing a travel time delay on the A9 that is significant enough to require re-routing of traffic from the north bound for Munich onto the A921A99 . In order to study the new control strategies the different OD-flows of traffic demand and the possible combinations of destinations, which can be displayed on the extended variable direction signs, have to be considered in the model. The normal signing of the variable message signs of destinations served as the reference case, as described in figures 2. and 3. as R... and Ra.
With this approach a realistic traffic volume of the network can be achieved and the main traffic related impacts can be estimated. The environmental impact models are based on traffic volumes and further attributes of the network description to determine emissions like noise level, CO2 and NOx and energy consumption.
To be able to determine the routes within NEMO in an appropriate manner. i.e. a fixed routing on the motorway network following the VDSs the shortest
The analysis of strategic measures can be carried out with STRAMA, using NEMO as an evaluation tool. With STRAMA the parameters of NEMO can be modified (like the network supply or the traffic
1107
path algorithm had to be extended in two dimensions: 1. Because of the fact, that the model is handling the total traffic network, which means all categories of roads, there is a high risk, that the shortest path algorithm is diverted from the main roads. This applies in particular in case of high volumes on links which lead to increased travel times. Therefore the network is improved in terms of the order of links emanating from nodes with respect to the road class to which a link belongs. With this approach the algorithm can easily reduce the searching through the main road elements (s. a Sheffi, 1986). 2. To ensure that the model is following the predefined routes (A\,A2 , .. R A ,B), ... ) defined by the locations of the variable direction signs the best path search from an origin to a destination has to be done through fixed points (Fig. 5). Origin
routed. The impacts are calculated for all route combinations and compared to each other in the selection procedure as described in Fig. 6.
5. CONCLUSION The development of an approach to collective route guidance integrating urban and interurban roads into alternative routes requires modelling tools capable of dealing with real time data and harmonising motorway and urban digital network. The requirements of strategic planning had to be met by the modelling tool-set NEMO/STRAMA which is to be used for simulation. A simulation approach meeting the requirements for the assessment of the envisaged re-routing strategies was designed. The feasibility study carried out demonstrated potentials for optimising the existing collective route guidance. The simulation method designed, fonns the basis for the elaboration and full assessment of new network control strategies.
Fh,1KI Point
REFERENCES
'...--00- 0 -
Akcelik, R. (1978). A new look at Davidson's travel time function. National Capital Development Commission, Canberra, Australia. Cremer, M.; Keller, H. (1991). Dynamic Identification of Flows from Traffic Counts of Complex Intersections. Proceedings of the Eigth
Oestina~on
Fig. 5: Routing through fixed points
International Symposium on Transportation and Traffic Theory, pp. 121 - 142, University of
Network State with asigned traffic without !be traffic co be rerou1
I
D
Toronto Press, Toronto. Hoops, M.; H. Keller and F. Busch (1997).
I
Netzmodellierung zur Erstellung eines Verkehrslageberichts in einem Strategie- und Servicezentrum am Beispiel Munich COMFORT.
cm
Munich Sachse, T . (1995). VARIA - Variable Message Sign Control Based On OD-Estimation In A Motorway Network. Proceedings for the Lu.MD
Route combinalions 81 82
R.
~~
R.t±±=±j
European Conference on Advanced Transport Telematics. Munich. Sachse, T. and A. CsalIner (1995). Advanced Regional Traffic Control Systems: Integration of AIDA and VARIA. Munich COMFORT Deliverable No. 4016. Munich Sheffi, y. (1986). Urban Transportation Networks, Equilibrium Analysis with mathematical programming methods, wr Prentice Hall, Inc.
Auip traffic for all roue. combinalions with respecI co cbeir
traffic volumes Ref~C....
Van Zuylen, H.J. (1981). Some Improvements in the Estimation of an OD-Matrix from Traffic Counts. Proceedings of the Eight International
Fig. 6: Decision procedure STRAMA is extended in order to handle predefined routes and to modify the matrices for regional area and the urban area. The matrices reduced by the amount of traffic going to be
Symposium on Transportation and Traffic Theory, pp. 656 - 671, University of Toronto
the the are re-
Press, Toronto.
1108
AN INTEGRATED APPROACH TO COLLECTIVE ROUTE GUIDANCE Marcus Hoops Maria Tsavachidis
Institute afTraffic Engineering and Planning, Technical University afMunich (FGV TUM) Arcisstr. 21, 80333 Munich, Germany
Abstract: In Munich only limited re-routing strategies have so far been applied to the existing network control system. New control strategies considering the different 00flows of traffic demand and the possible set of route combinations for chosen destination areas are investigated in a feasibility study. Because only limited destination zones can be displayed by the existing variable direction signs new re-routing strategies have to be assessed in a simulation environment. An integrated approach for defining, simulating and evaluating new re-routing strategies is developed, using the network monitoring tool NEMO and the strategy simulation tool STRAMA Keywords: Traffic Control, Simulation, State Estimation, Evaluation, State Monitoring
was to facilitate an integrated traffic management. The architecture required for that is mainly based on a traffic information pool and strategy and service centre (TIP/SSC) linking various important subsystems. One of the main measures for urbanIinterurban control in Munich is a collective route guidance system at the fringe of the urban and motorway network to the north (Fig. 1).
1. BACKGROUND
Constant traffic increase and exhausted network capacities in conurbation areas have commonly led to intensified efforts in the development of new approaches to network control Munich like other major urban centres suffers from increasing traffic demand and its related environmental and economic impacts to a degree which can no longer be solely met by infrastructural measures, i.e. a continuous adaption of the network to new levels of demand. It is therefore sought to develop and apply new traffic control and management systems which can make demand comply with the existing network rather than vice versa.
Only limited re-routing strategies have so far been applied due to the lack of appropriate strategies and diverging interests of the responsible authorities. The main conflict in defining optimal re-routing recommendations for the VDS system lies in diverging interests of Munich's municipality and the Freestate of Bavaria being responsible for the urban and motorway network respectively. While the motorway authority supports the diversion of traffic from their network onto urban arterials to increase traffic flow on the motorways, the city of Munich generally objects to additional traffic being induced onto urban roads where it is assumed to add to traffic
The future development of a coherent traffic management system for the wider area of Munich will be based on work done in the LLAMD Munich COMFORT (COoperative Management FOr urban and Regional Transport) project (Munich COMFORT. Apart from applying and assessing a set of traffic control and management systems a main objective
1103
related problems, which moreover effect areas of higher population density. Despite this conflict of interest the insight into an obvious need for harmonised control strategies is reflected by joined participation of both authorities in research activities on the integration of urban and inter-urban control (i.e. TABASCO, EC DG XIII . Transport Telernatics Programme). Specific tools are required to optmuse traffic planning and strategy development reflecting the characteristics of traffic demand and traffic related impacts in compliance with urban and interurban policies.
fringe of the urban network. The value of the diversion is not only limited due to this critical merging at the intersection but also due to the alternative route being app. 60% longer than the normal route. The direction signs installed do not allow for a diversification of diverting traffic to Munich by city districts, as only Munich and some long distance destinations are displayed. Therefore for some destinations the alternative route is not suitable for providing any significant benefit. Recognising the need for new re-routing models, the Technical University of Munich has developed the alternate routing algorithm V ARIA based on dynamic OD-estimation (Sachse, 1995). V ARIA will be integrated with an incident detection tool implemented on a main urban arterial, for a field trial on urban integrated traffic control in the Munich COMFORT test area. Although being a first step into more sophisticated collective route guidance, a wider range of strategies has yet to be developed
3. AN INTEGRATED APPROACH TO ALTERNATE ROUTING
3. J Selection of alternative routes The objective of this study was to develop a sophisticated approach to collective route guidance for an extended Munich COMFORT test site in showing potentials of other alternative routes using both motorway and urban network. To minimise adverse impacts on the urban arterials new rerouting strategies taking into account more distinct destination areas than are currently displayed by the VDS are investigated. Thereby it is intended to obtain alternative routes that are better adapted to the given ODs in the network.
~ VoriObie Oire<:tton Siqn
Fig. 1. Munich: Re-routing Network
In conjunction with respective work currently being undertaken within the TABASCO project, new strategies for collective route guidance complying with both urban and interurban policies were developed for the study area comprising both motorways and urban arterials. A network monitoring tool NEMO (NEtwork Monitor) was used off-line for the iterative selection of re-routing strategies (Hoops, et al., 1997). To facilitate the envisaged strategy assessment and calculation of potential benefits of this integrated re-routing approach a concept for a simulation with NEMO was developed.
Especially for traffic bound for destinations that are not near the access point of the A9 motorway other alternative routes seem to be more obvious than the current one, which serves as reference route. This applies in particular to traffic destinations in the western, south-western and southern parts of Munich. The OD-Matrix of the motorway shows that about 45% of traffic at the interchange Neufahrn, being the first decision point for the re-routing of traffic, is bound for Munich. After leaving the motorway a total of 90% of this traffic is allocated to two main urban arterials which drivers could easily access through other alternative routes. About 20% of the total traffic coming from the North and bound for Munich are heading for western and south-western parts and app. 30% for central and southern parts of Munich. Although it must be assumed that a share of
2. CURRENT NETWORK CONTROL PRACTICE Currently in case of an incident or congestion on the normal motorway route A9 to Munich, traffic is being diverted by variable direction signs to the bypass motorway route. Traffic on the normal and alternative route meet again at an intersection on the
1104
this traffic already uses routes other than the motorway A9 there still lies significant potential for re-routing the remaining traffic onto better alternatives.
The best alternative route selected for destinations in the centre and south of Munich holds potential for a 5,5% reduction in travel time and 17% in travel distance whereas the second route requires similar travel time, due to much lower mean speed but travel distance is about 30% reduced compared to the conventional route (Fig. 3).
For the selection of best routes the network monitor NEMO was used working on the basis of historical data. Congestion on the A9 was simulated thus making the router select other 'best' routes in terms of minimum individual travel time derived from mean speed and route length.
Munich -
Central South
One destination point was chosen to represent destinations of West/ Southwest Munich and Munich Centre/South respectively. For the best alternative route detennined for destination area West/SouthWest (Fig. 2) a reduction of 29% in travel time and 28% in travel distance in comparison to the conventional re-routing strategy was calculated. The showed best route holds a 10% and 16% reduction in travel time and distance respectively.
-Re ••• 81
_ •• 82
,
Munich· \ West I South-West"
-RA •••
A1
... - A:2.
. . . .__\
m
"'"" 89
30730
1175
no
250158
'251
60
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MC
RB
1243
B'
B2
1U71 _ _. . .~_..,.-+
Fig. 3. Alternative routes destinations
1451 A1
1311
25365 81
central/southern
Both new routes incorporate the urban arterial Ingolstaedterstrasse whereas the conventional route runs fully on the motorway network. Within the DRIVE IT project LLAMD / Munich COMFORT and the follow up project T ABASeO the possible use of the Ingolstaedterstrasse for alternate routing strategies was examined (Sachse and Csallner, 1995). It became evident that capacity resources for additional re-routed traffic exist only during limited time periods, which is partly due to a poor performance of the urban traffic control. Therefore currently these periods of free capacity do mostly not coincide with congestion periods on the A9. In case of incidents though, traffic flow on the motorway is disturbed to a degree which could make the urban arterial preferable in terms of overall adverse impacts.
87
1Q26
for
F
FGV·TUM
Fig. 2. Alternative routes for south/south-western destinations Looking at the distance travelled on urban roads, the one included in the conventional route is not significantly shorter or even longer than the alternatives. Thus diverting traffic onto urban arterials can be beneficial not only in terms of a reduction in adverse impacts on the overall network but also specifically on the urban network itself.
Although only to be seen as a rough estimate, as no real time data e.g. for peak periods was used, the offline calculation facilitated the choice of appropriate alternative routes and gave a rough picture of the potentials to be expected.
1105
The selected routes fonn the basis for the integrated re-routing approach to be developed.
3.2 Strategic Approach To be operational, new strategies have to be highly distinct and specified in terms of decision criteria. This requires above all verification and strategy assessment taking into account differences of traffic situations over time of day. The prerequisite for both operation and simulation is the identification of destination shares. For simulation these are derived from an historical matrix and applied on the actual traffic volume at the decision interchange Neufahm. Relevant streams are respectively allocated to all possible combinations of alternative routes chosen, fonning the set of variable re-routing strategies. The latter have to be assessed in detail with regard to travel time, energy consumption and environmental impacts in the study area. Variable choice of route combinations mainly taking into account capacity on the urban arterials affected, opens a wider range of possibilities, as traffic can be allocated evenly on the network optimising network efficiency overall. 4. INVESTIGATION BASED ON SIMULATION
4.1.
Context
Due to political restrictions and lack of appropriate installation the new strategies were not applicable in a field trial. In order to be able to evaluate re-routing strategies under conditions nearest to reality a simulation study was chosen.
simulation model is the uncertainty of the traffic state prognosis for complex traffic networks. Assignment models on the other hand are less accurate in the description of vehicle movements, because no in-depth traffic flow model is used. Nevertheless flow propagation models are reliable in estimating the mean traffic state based on OD-flows and less demanding in calculation.
4.2
The models NEMO and STRAMA
The actual implementation of the online-version of the Network Monitor (NEMO) was developed in the LLAMDlMunich-Comfort project (Hoops, 1997). It's main objective is the description of the traffic state in urban and rural networks. It is supplied with dynamic traffic counts, to some extend with traffic states and with the state of signalised intersections by traffic information centres through the Strategy and Service Centre (SSC). NEMO establishes the context of the data locally collected in space and time for the whole test site and derives traffic related impacts, such as travel time, delay time, emissions and energy consumption. Through traffic models the traffic state in the network is estimated in terms of traffic volume, speed, travel time and proportion of "traffic volume to capacity". In addition, based on the estimated traffic state, environmental variables like carbon monoxide, nitrogen oxides etc. are estimated . All these variables can be described by NEMO on the level of classes but not in terms of exact numbers as the traffic information available is not sufficient for a network as complex as the one examined by NEMO.
A main benefit of the simulation study lay in its independence from technical constraints in the field, e.g. the restricted set of messages of the Variable Direction Signs limiting the possibilities for a distinction between destination zones in Munich (e.g. Munich-CBD and Munich-West). A shortcoming of simulation studies in general can be a lack of confidence of the tools being used. The quality of the used network monitoring tool (NEMO) though, was demonstrated in the framework of an evaluation within the Munich COMFORT project.
Network Monitor NEMO is using a traffic network model which was derived from a digital road map of a common supplier for the test site Munich, traffic models like traffic assignment. origin-destination estimator (Van Zuylen, 1981), a queuing model (Kimber-Hollis), a capacity estimator (specifically for intersections), a simple traffic flow model and impact models to estimate the impacts like emissions and energy consumption (Fig. 4.).
In general the monitoring of the traffic impacts is based on the available traffic data in the SSC. Gaps in data are closed by using historical information or by interpolation.
The software tools were used for a first comparative evaluation of different alternative routes based on the traffic situation on the relevant stretches of the network. Thereby traffic demand was modified in order to simulate different scenarios and to compare them to the reference case.
Data are collected from the regional traffic control centre and urban control centre. In the urban control centre traffic flow data (i. e. traffic volume, speed and occupancy), the state of the signalised intersections and the actual selected signal plan are
In general such an investigation based on simulation can be perfonned with a simulation tool like a time propagation model or an assignment tool, which is a flow propagation model. The problem of applying a
1106
available. Traffic data and the actual OD-matrix are provided by the regional traffic control centre. NEMO network elements are intersections and links. A queuing model for intersections and a simple traffic flow model (Akcelik, 1978). for the links are being used. In the urban area one link between two intersections is described by a speed-flow-relation. The focus in urban areas lies on the realistic description of the intersections. In the rural area those arcs are linked together with individual speedflow-relation to describe the traffic behaviour on long motorways. With this approach big networks can be modelled. The actual network for the in-depth modelling analysis is at present limited to the Munich-COMFORT test site. This means the motorway network north of Munich and an urban area of approximately 220 signalised intersections, which represents 20% of the whole city area.
demand) in order to evaluate for example new traffic scenarios. STRAMA is comparing the network state for the 'with' and 'without' case. Within the project Munich COMFORT STRAMA was developed to handle the modification of some variable of network supply like change in the number of lanes, turning restrictions, lane blocking and speed limits. NEMO Internal Interaction between the Models
Global Data Base tor NEMO
OD-Estlmatlon at single intersections
+
Trat!ic Network Description. Dynamic T rafIic Data-8ank, Oescriplion of complex inletSeClions SIgnalIsation Historical OD-Matrix
OD-Estimation in Networ1
For the assignment procedure trip matrices are necessary. Whereas for the regional area a dynamic matrix is provided by the control centre, there is none available for the urban area. Therefore a historical matrix of the city's planning department was used. This matrix is based on average daily traffic (AD1). To make use of this matrix in NEMO it has to be disaggregated into one hour time intervals. The derived matrices will be updated by online counts in the network and an OD-estirnator based on the Van Zuylen (1981) approach.
Capacity E.s1imation Queue Model Flow-Speed ModeII
~ AssIgnment Path Flow Opnmisation in the network
1
I:=!
Cost Function (Travel Time)
~
Best Route Search
I
Traffic State of the Network
~
Environmental Modells
Analysis
Fig. 4. Model elements of NEMO
As the regional and the urban network in the investigation area are connected, the matrices have to be linked with respect to some origins and destinations, i.e. those at the fringe of both networks. The one hour matrices are assigned to the network according to the volume and the derived costs on the individual links. Two methods are used for assignment, i.e. the incremental and the user equilibrium assignment. The best approach is selected during the test period of NEMO. Because of the unreliability of the urban OD-matrix the assignment procedure was extended with a path-flow optimisation, which tries to fit the path-flows with the traffic counts on the links.
Model Extension For investigating the alternative routing strategies some extensions of the NEMO and STRAMA tools were necessary. For carrying out an off-line investigation it appeared to be necessary to emulate first the base framework, i.e. a congestion on the A9 between the intersections Neufahrn and MunichNorth. This is realised by introducing a travel time delay on the A9 that is significant enough to require re-routing of traffic from the north bound for Munich onto the A921A99 . In order to study the new control strategies the different OD-flows of traffic demand and the possible combinations of destinations, which can be displayed on the extended variable direction signs, have to be considered in the model. The normal signing of the variable message signs of destinations served as the reference case, as described in figures 2. and 3. as R... and Ra.
With this approach a realistic traffic volume of the network can be achieved and the main traffic related impacts can be estimated. The environmental impact models are based on traffic volumes and further attributes of the network description to determine emissions like noise level, CO2 and NOx and energy consumption.
To be able to determine the routes within NEMO in an appropriate manner. i.e. a fixed routing on the motorway network following the VDSs the shortest
The analysis of strategic measures can be carried out with STRAMA, using NEMO as an evaluation tool. With STRAMA the parameters of NEMO can be modified (like the network supply or the traffic
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path algorithm had to be extended in two dimensions: 1. Because of the fact, that the model is handling the total traffic network, which means all categories of roads, there is a high risk, that the shortest path algorithm is diverted from the main roads. This applies in particular in case of high volumes on links which lead to increased travel times. Therefore the network is improved in terms of the order of links emanating from nodes with respect to the road class to which a link belongs. With this approach the algorithm can easily reduce the searching through the main road elements (s. a Sheffi, 1986). 2. To ensure that the model is following the predefined routes (A\,A2 , .. R A ,B), ... ) defined by the locations of the variable direction signs the best path search from an origin to a destination has to be done through fixed points (Fig. 5). Origin
routed. The impacts are calculated for all route combinations and compared to each other in the selection procedure as described in Fig. 6.
5. CONCLUSION The development of an approach to collective route guidance integrating urban and interurban roads into alternative routes requires modelling tools capable of dealing with real time data and harmonising motorway and urban digital network. The requirements of strategic planning had to be met by the modelling tool-set NEMO/STRAMA which is to be used for simulation. A simulation approach meeting the requirements for the assessment of the envisaged re-routing strategies was designed. The feasibility study carried out demonstrated potentials for optimising the existing collective route guidance. The simulation method designed, fonns the basis for the elaboration and full assessment of new network control strategies.
Fh,1KI Point
REFERENCES
'...--00- 0 -
Akcelik, R. (1978). A new look at Davidson's travel time function. National Capital Development Commission, Canberra, Australia. Cremer, M.; Keller, H. (1991). Dynamic Identification of Flows from Traffic Counts of Complex Intersections. Proceedings of the Eigth
Oestina~on
Fig. 5: Routing through fixed points
International Symposium on Transportation and Traffic Theory, pp. 121 - 142, University of
Network State with asigned traffic without !be traffic co be rerou1
I
D
Toronto Press, Toronto. Hoops, M.; H. Keller and F. Busch (1997).
I
Netzmodellierung zur Erstellung eines Verkehrslageberichts in einem Strategie- und Servicezentrum am Beispiel Munich COMFORT.
cm
Munich Sachse, T . (1995). VARIA - Variable Message Sign Control Based On OD-Estimation In A Motorway Network. Proceedings for the Lu.MD
Route combinalions 81 82
R.
~~
R.t±±=±j
European Conference on Advanced Transport Telematics. Munich. Sachse, T. and A. CsalIner (1995). Advanced Regional Traffic Control Systems: Integration of AIDA and VARIA. Munich COMFORT Deliverable No. 4016. Munich Sheffi, y. (1986). Urban Transportation Networks, Equilibrium Analysis with mathematical programming methods, wr Prentice Hall, Inc.
Auip traffic for all roue. combinalions with respecI co cbeir
traffic volumes Ref~C....
Van Zuylen, H.J. (1981). Some Improvements in the Estimation of an OD-Matrix from Traffic Counts. Proceedings of the Eight International
Fig. 6: Decision procedure STRAMA is extended in order to handle predefined routes and to modify the matrices for regional area and the urban area. The matrices reduced by the amount of traffic going to be
Symposium on Transportation and Traffic Theory, pp. 656 - 671, University of Toronto
the the are re-
Press, Toronto.
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