- Email: [email protected]
Environmentally Beneficial Intelligent Transportation Systems
Proceedings of the 12th IFAC Symposium on Transportation Systems Redondo Beach, CA, USA, September 2-4, 2009
Environmentally Beneficial Intelligent Transportation Systems Matthew Barth, Senior Member, IEEE and Kanok Boriboonsomsin Abstract— Intelligent Transportation Systems (ITS) have been developed over the years as a means to solve a variety of transportation problems. The primary objectives of ITS have been focused primarily on improving safety and increasing transportation efficiency. However, ITS can also have significant environmental benefits. There has been long term concern regarding vehicle pollution and associated air quality. More recently, there is an increased concern with energy consumption and greenhouse gas (GHG) emissions. Many existing ITS programs have the potential to reduce energy consumption and GHG emissions; however, it is also possible to specifically design ITS programs that minimize environmental impacts of transportation. In this paper, we briefly outline different kinds of ITS programs and their potential environmental benefits. We then review several ITS research projects being carried out in Southern California that are specifically targeting reductions in energy consumption and GHG emissions. Index Terms—intelligent transportation systems, energy, environment.
I
I. INTRODUCTION
ntelligent Transportation Systems (ITS) have generated considerable enthusiasm in the transportation community as a potential means to improve roadway safety, reduce congestion, and enhance the mobility of people and goods. In addition, ITS has the potential to reduce energy consumption and vehicle pollutant and greenhouse gas emissions. Because of increased concerns about energy and environmental issues, the goal of this paper is to highlight specific ITS programs that are environmentally beneficial. Current transportationrelated energy and environmental problems will not be solved with a single solution; a multitude of solutions will be necessary. In addition to designing and implementing environmentally-friendly vehicles and fuels, as well as slowing total travel growth, ITS can play an important role. Intelligent transportation systems consist of a wide variety of technologies and applications. In general, these can be categorized into three major areas: Advanced Vehicle Control and Safety Systems (AVCSS); Advanced Transportation Information Systems (ATIS); and Advanced Transportation Management Systems (ATMS) [1]. Section II of this paper
M. Barth is with the electrical engineering department and the College of Engineering-Center of Environmental Research and Technology (CE-CERT), University of California, Riverside, CA 92507 USA (email: [email protected]). K. Boriboonsomsin is with CE-CERT, University of California, Riverside, CA 92507 USA (e-mail: [email protected]).
978-3-902661-50-0/09/$20.00 © 2009 IFAC
provides a very brief outline of these areas with a focus on their potential impacts on energy and the environment. Sections III, IV, and V then present some specific examples of energy/environmental ITS programs in each of the areas— AVCSS, ATIS, and ATMS—respectively. Conclusions and future work are then provided in Section VI. II. ITS USER SERVICES According to the ITS America National Transportation Plan [1], different ITS technology and applications can generally be grouped into user service “bundles”. The major user services include AVCSS, ATIS, and ATMS, as described below. A. Advanced Vehicle Control and Safety Systems There are several examples of ITS technology that are focused on the vehicle itself. Because of the high number of accidents that occur on today’s roads, better safety systems are being developed. In terms of collision avoidance, there are active research programs in: Longitudinal Collision Avoidance Systems which are concerned with front and rear-end collisions. On-board radar, LIDAR, and computer vision technology is being applied to monitor headways between vehicles, and using feedback to the vehicle’s braking system, collisions can be reduced. These sensor systems are also being used for Advanced Cruise Controls (ACC) that not only allow a driver to select a desired speed, but also allow setting the following distance. Lateral Collision Avoidance Systems are concerned with collisions that occur during lane changes or turning. Computer vision technology and other sensors are being deployed to reduce lateral collisions. In addition, there is active research in the related area of lane departure warning. Intersection Collision Avoidance Systems are another important area of research since many accidents occur at road crossings and intersections. New monitoring sensors and communication systems are being integrated to provide drivers with better information about traffic at intersections, thereby reducing the number of accidents. Other ITS technologies in this area deal with safety readiness and pre-crash restraint deployment if any type of collision is imminent. The sensor and control systems being developed for
342
10.3182/20090902-3-US-2007.0086
12th IFAC CTS (CTS 2009) Redondo Beach, CA, USA, September 2-4, 2009
collision avoidance are directly applicable to implementing partial or full automation, culminating in automated highway system (AHS) implementations. In these AHS implementations, vehicles are able to automatically drive themselves with little input from the passengers. It is clear that reducing the number of accidents on the roadway is beneficial from a safety perspective; they also have a benefit in improving overall traffic efficiency, causing less congestion and smoother traffic flow. There are also significant energy and emissions benefits to this congestion mitigation and smoother traffic flow. When vehicles travel in slower, stop-and-go traffic, their energy consumption and emissions are significantly higher compared to traveling at steady, higher speeds (i.e., less acceleration/decelerations at speeds around 80 kph for most light-duty vehicles). Therefore, any type of congestion mitigation is beneficial from an environmental perspective. However, it is important to note that traveling at much higher speeds (e.g., 100 kph and above) will increase fuel consumption and emissions due to aerodynamic drag effects. B. Advanced Traveler Information Systems Developed primarily as a convenience to drivers, ATIS technology includes items such as: Route Guidance Systems that include both on- and offboard navigation systems that select routes in a roadway network from a specific origin to a specific destination. These systems attempt to minimize some criteria, such as travel time or travel distance. These navigation systems often include an en-route driver information database, which can help guide drivers to specific goals (e.g., gasoline filling station, open parking space). Electronic Payment Systems are often included in this area, allowing for the payment of tolls and fees without stopping the vehicle to complete the financial transaction. Not only are these different systems convenient for the traveler, but they also have a significant benefit for reducing energy consumption and emissions. A route guidance system will cut back on unnecessary travel that may occur when a driver gets lost or chooses a long, out-of-the-way path. Enroute driver information is also beneficial by eliminating the additional energy consumption and emissions associated with driving around, searching for these specific goals. And electronic payment systems eliminate the need for a driver to decelerate the vehicle, idle while a manual transaction takes place, followed by an acceleration that gets the vehicle back up to a desired speed. If this payment can occur without slowing down, emissions and energy consumption are reduced. C. Advanced Transportation Management Systems It is clear that as a roadway network gets increasingly congested due to high travel demand, it is necessary to have good monitoring and management systems: Traffic Monitoring Systems are improving with better
sensor technology and with advances in the information processing. In addition to providing transportation managers with better real-time information, new data processing techniques are being developed to estimate traffic flow, density, and speed. Incident Management is also important in terms of early detection of incidents (i.e., accidents, lane closures, etc.) and swift removal of these incidents so traffic can begin to flow smoothly again. Corridor Management techniques are applicable to freeway networks (e.g., ramp metering) and to signalized arterial networks (e.g., signal synchronization). These techniques are designed to keep traffic flowing as smoothly as possible through the corridor, greatly reducing the amount of idling. Travel Demand Management is another important part of ATMS. Reducing the number of vehicles on a congested roadway through pricing and other techniques can significantly improve traffic flow. All of these ATMS components can have a large impact in reducing energy consumption and emissions. In general, all efforts to keep traffic flowing smoothly at moderate speeds will minimize environmental impacts. Travel demand management goes even further by reducing the number of vehicles in the transportation system, thereby reducing overall energy and emissions. Specific environmental benefits for most of these AVCSS, ATIS, and ATMS implementations have been presented in the literature. For the most part, the quantified benefits are highly dependent on the specific implementation. The benefits of some implementations may be small. However, by implementing many of these technologies simultaneously, significant energy and emission reductions are possible. In the next few sections, we outline several example projects in the fields of AVCSS, ATIS, and ATMS. III. VEHICLE PLATOONING As described in Section II, an automated highway system consists of a variety of AVCSS systems to improve the safety and efficiency of highway travel. In addition, there are several potential environmental benefits: 1) vehicle fuel consumption and emissions will be reduced due to smoother traffic flow (i.e., fewer accelerations/decelerations) and less congestion, resulting in shorter trip times; and 2) if vehicles operate at very close spacings (i.e., platooning, as shown in Fig. 1), the aerodynamic drag on the vehicles will be lower and fuel consumption and emissions will be further reduced. It has been estimated that aerodynamic drag can account for up to 50% of the required energy when traveling at highway speeds. In order to estimate the potential emissions and fuel consumption benefits of an AHS, both simulation and realworld experimentation was carried out as part of the U.S. National Automated Highway System Consortium 1997 Demonstration in San Diego, California [2]. As part of this research, a detailed AHS microsimulation transportation
343
12th IFAC CTS (CTS 2009) Redondo Beach, CA, USA, September 2-4, 2009
model was combined with a comprehensive modal emissions model to predict emissions and energy use for a variety of modeled highways. The predicted AHS emissions and fuel consumption were compared against a variety of scenarios, including: 1) non-automated traffic at different levels of congestion; and 2) idealized traffic flow.
consumption and vehicle emissions, as shown in Fig. 3. These methods combine sophisticated vehicle energy and emission models with route minimization algorithms that are used for navigational purposes. These new methods have been applied to several Southern California case studies resulting in significant energy and emissions savings compared to standard navigation techniques [4].
Fig. 1: Platoon of light-duty vehicles in NAHSC Demo 97 (image courtesy of California PATH Program).
In Fig. 2, fuel consumption per unit distance (given in grams per mile) per vehicle is shown as a function of average vehicle speed for the scenarios of non-automated traffic, ideal constant-speed traffic, and AHS travel. The solid line represents the non-automated traffic scenario, where the data points represent the average fuel consumption for different congestion levels (see [2]). The dashed line represents the ideal constant-speed scenario (i.e., traffic without any acceleration/deceleration events) and could be regarded as the lower limit of emissions for the vehicle at different constant speeds. Results for two AHS scenarios (cooperative and cooperative-platooned) are shown to lie between the ideal minimum and the non-automated traffic under light congestion. The platoon-based AHS showed lower fuel consumption (approximately 5-10%) due to aerodynamic drag reduction when vehicles operate at close spacings. This platooning research has also been conducted with heavy-duty trucks, operating at different spacings [3]. Because trucks have greater aerodynamic effects, greater fuel and carbon dioxide (CO2) savings were achieved, in the range of 10-15%. IV. ENVIRONMENTALLY-FRIENDLY NAVIGATION As an example of ATIS technology, recent research has been conducted in developing navigational systems that specifically target reducing fuel consumption and emissions [4]. Many of today’s navigation systems help guide drivers to their destinations; more sophisticated systems also help drivers avoid congestion on the roadways based on real-time traffic information. These navigation systems have embedded algorithms that attempt to minimize trip distance and/or travel time. By taking this one step further, new navigation techniques have been developed that focus on minimizing energy
Fig. 2: Fuel consumption versus average cycle speed for different AHS scenarios.
In these studies, it was found that in many cases, a timeminimization path also minimizes energy and emissions. However, when congestion occurs, there are cases where this is not true. Because energy and emissions are often higher at congested speeds, a heavily congested (but shorter) path may not be the most environmentally friendly. In contrast, moderate congestion often provides a better choice from an energy and environmental perspective. Moderate congestion generally reduces average traffic speeds from higher free-flow conditions, where vehicles have increased fuel consumption and emissions due to higher loads placed on the vehicle engines. Using historical data of two comparable freeways in the Los Angeles area, it was shown that for almost half of the time, the developed energy/environmentally-friendly navigation system can help a driver choose the best travel route that consumes the least fuel and/or produces the least amount of emissions. This may be highly desirable during the time period when fuel prices continue to hit record high and global warming as well as climate change have become major concerns worldwide. V. DYNAMIC ECO-DRIVING As another strategy to reduce emissions and save fuel, ecodriving is gaining increasing interest worldwide. Eco-driving typically consists of changing a person’s driving behavior based on general static advice to the driver (e.g., do not accelerate too quickly, reduce speeds, etc.). Using ITS technology, it is possible to enhance eco-driving strategies and make it dynamic, where advice is given in real-time to
344
12th IFAC CTS (CTS 2009) Redondo Beach, CA, USA, September 2-4, 2009
drivers based on changing traffic conditions in the vehicle’s vicinity [5]. This dynamic eco-driving strategy takes advantage of real-time traffic sensing and telematics, allowing for a traffic management system to monitor traffic speed, density, and flow and then communicate advice (e.g., recommended speed) in real-time back to the vehicles (as depicted in Fig. 4). By providing dynamic advice to drivers, approximately 10% to 20% in fuel savings and lower CO2 emissions are possible using a simple strategy that smoothes traffic flow during congested conditions without a significant loss of travel time (typically less than 5%) as shown in Table 1. Based on extensive simulation experiments, it was found that in general, higher percentage reductions occur during severe congestion (e.g., LOS E-F) compared to less congested scenarios. Real-world experiments have also been carried out, showing similar reductions but to a slightly smaller degree.
wide range of technology and applications, and most do have an environmental benefit. However, the environmental benefits can be maximized when these ITS applications are “tuned” so that emissions and fuel consumption are specifically reduced. Further, it is important to point out that there will not be a single solution to addressing these environmental issues. Each ITS environmentally-beneficial implementation will likely have improvements in the range of 5% - 15%. However, most solutions are additive, therefore greater benefits can be achieved when a multitude of environmentally-friendly ITS programs are put into place. Instrumented Vehicles
Embedded Road Sensor Data
Traffic Management Center
Traffic Management Center
Traffic Performance Measurement System (PeMS)
Traffic Management Center
Wireless Communications Provider
System Server
Vehicle Data
Internet
Fig. 4: Overall system architecture for real-world experimentation of dynamic eco-driving. Fig. 3: Example snapshot of the environmentally-friendly navigation system showing routes that have lower costs of energy and emissions.
ACKNOWLEDGMENTS The authors would like to acknowledge the University of California’s Energy Institute (UCEI), the University of California Transportation Center (UCTC), the California PATH Program, and the California Department of Transportation for partial sponsorship of this research. The contents of this paper reflect the views of the authors and do not necessarily indicate acceptance by the sponsors.
Table 1: Emissions and fuel consumption differences between non-ecodriving and dynamic eco-driving strategy (from [5]).
Energy/Emissions
Non -ECO
ECO
Difference
CO2 (g)
5439
4781
-12%
CO (g)
97.01
50.47
-48%
HC (g)
3.20
1.90
-41%
NOx (g)
6.28
3.97
-37%
Fuel (g)
1766
1534
-13%
REFERENCES [1]
VI. SUMMARY The goal of this paper is to highlight specific ITS programs that are environmentally beneficial, spanning the three main areas of ITS, including Advanced Vehicle Control and Safety Systems, Advanced Transportation Information Systems, and Advanced Transportation Management Systems. Although these ITS programs have been targeted at improving safety and reducing congestion, it can also be very beneficial for reducing fuel consumption and lowering emissions from transportation. ITS technology consists of a
ITS America, “National Intelligent Transportation Systems Program Plan”, technical report, Intelligent Transportation Society of America, Washington, D.C., see http://www.itsa.org”, 2002. [2] M. Barth, “An emissions and energy comparison between a simulated automated highway system and current traffic conditions”, Proceedings of the 2000 IEEE Intelligent Transportation Systems Conference, Dearborn, MI, Oct. 2000. [3] Browand, F., J. McArthur, and C. Radovich, “Fuel Saving Achieved in the Field Test of Two Tandem Trucks”, California PATH Research Report, report number UCB-ITS-PRR-2004-20, 2004. [4] M. Barth, K. Boriboonsomsin, and A. Vu, “Environmental-friendly navigation,” Proceedings of the 10th International IEEE Conference on Intelligent Transportation Systems, Seattle, WA, September 30 – October 3, 2007. [5] M. Barth and K. Boriboonsomsin, “Energy and Emissions Impacts of a Freeway-Based Dynamic Eco-Driving System”, in press, Transportation Research Part D: Environment, Elsevier Press, 2009.
345
Environmentally Beneficial Intelligent Transportation Systems Matthew Barth, Senior Member, IEEE and Kanok Boriboonsomsin Abstract— Intelligent Transportation Systems (ITS) have been developed over the years as a means to solve a variety of transportation problems. The primary objectives of ITS have been focused primarily on improving safety and increasing transportation efficiency. However, ITS can also have significant environmental benefits. There has been long term concern regarding vehicle pollution and associated air quality. More recently, there is an increased concern with energy consumption and greenhouse gas (GHG) emissions. Many existing ITS programs have the potential to reduce energy consumption and GHG emissions; however, it is also possible to specifically design ITS programs that minimize environmental impacts of transportation. In this paper, we briefly outline different kinds of ITS programs and their potential environmental benefits. We then review several ITS research projects being carried out in Southern California that are specifically targeting reductions in energy consumption and GHG emissions. Index Terms—intelligent transportation systems, energy, environment.
I
I. INTRODUCTION
ntelligent Transportation Systems (ITS) have generated considerable enthusiasm in the transportation community as a potential means to improve roadway safety, reduce congestion, and enhance the mobility of people and goods. In addition, ITS has the potential to reduce energy consumption and vehicle pollutant and greenhouse gas emissions. Because of increased concerns about energy and environmental issues, the goal of this paper is to highlight specific ITS programs that are environmentally beneficial. Current transportationrelated energy and environmental problems will not be solved with a single solution; a multitude of solutions will be necessary. In addition to designing and implementing environmentally-friendly vehicles and fuels, as well as slowing total travel growth, ITS can play an important role. Intelligent transportation systems consist of a wide variety of technologies and applications. In general, these can be categorized into three major areas: Advanced Vehicle Control and Safety Systems (AVCSS); Advanced Transportation Information Systems (ATIS); and Advanced Transportation Management Systems (ATMS) [1]. Section II of this paper
M. Barth is with the electrical engineering department and the College of Engineering-Center of Environmental Research and Technology (CE-CERT), University of California, Riverside, CA 92507 USA (email: [email protected]). K. Boriboonsomsin is with CE-CERT, University of California, Riverside, CA 92507 USA (e-mail: [email protected]).
978-3-902661-50-0/09/$20.00 © 2009 IFAC
provides a very brief outline of these areas with a focus on their potential impacts on energy and the environment. Sections III, IV, and V then present some specific examples of energy/environmental ITS programs in each of the areas— AVCSS, ATIS, and ATMS—respectively. Conclusions and future work are then provided in Section VI. II. ITS USER SERVICES According to the ITS America National Transportation Plan [1], different ITS technology and applications can generally be grouped into user service “bundles”. The major user services include AVCSS, ATIS, and ATMS, as described below. A. Advanced Vehicle Control and Safety Systems There are several examples of ITS technology that are focused on the vehicle itself. Because of the high number of accidents that occur on today’s roads, better safety systems are being developed. In terms of collision avoidance, there are active research programs in: Longitudinal Collision Avoidance Systems which are concerned with front and rear-end collisions. On-board radar, LIDAR, and computer vision technology is being applied to monitor headways between vehicles, and using feedback to the vehicle’s braking system, collisions can be reduced. These sensor systems are also being used for Advanced Cruise Controls (ACC) that not only allow a driver to select a desired speed, but also allow setting the following distance. Lateral Collision Avoidance Systems are concerned with collisions that occur during lane changes or turning. Computer vision technology and other sensors are being deployed to reduce lateral collisions. In addition, there is active research in the related area of lane departure warning. Intersection Collision Avoidance Systems are another important area of research since many accidents occur at road crossings and intersections. New monitoring sensors and communication systems are being integrated to provide drivers with better information about traffic at intersections, thereby reducing the number of accidents. Other ITS technologies in this area deal with safety readiness and pre-crash restraint deployment if any type of collision is imminent. The sensor and control systems being developed for
342
10.3182/20090902-3-US-2007.0086
12th IFAC CTS (CTS 2009) Redondo Beach, CA, USA, September 2-4, 2009
collision avoidance are directly applicable to implementing partial or full automation, culminating in automated highway system (AHS) implementations. In these AHS implementations, vehicles are able to automatically drive themselves with little input from the passengers. It is clear that reducing the number of accidents on the roadway is beneficial from a safety perspective; they also have a benefit in improving overall traffic efficiency, causing less congestion and smoother traffic flow. There are also significant energy and emissions benefits to this congestion mitigation and smoother traffic flow. When vehicles travel in slower, stop-and-go traffic, their energy consumption and emissions are significantly higher compared to traveling at steady, higher speeds (i.e., less acceleration/decelerations at speeds around 80 kph for most light-duty vehicles). Therefore, any type of congestion mitigation is beneficial from an environmental perspective. However, it is important to note that traveling at much higher speeds (e.g., 100 kph and above) will increase fuel consumption and emissions due to aerodynamic drag effects. B. Advanced Traveler Information Systems Developed primarily as a convenience to drivers, ATIS technology includes items such as: Route Guidance Systems that include both on- and offboard navigation systems that select routes in a roadway network from a specific origin to a specific destination. These systems attempt to minimize some criteria, such as travel time or travel distance. These navigation systems often include an en-route driver information database, which can help guide drivers to specific goals (e.g., gasoline filling station, open parking space). Electronic Payment Systems are often included in this area, allowing for the payment of tolls and fees without stopping the vehicle to complete the financial transaction. Not only are these different systems convenient for the traveler, but they also have a significant benefit for reducing energy consumption and emissions. A route guidance system will cut back on unnecessary travel that may occur when a driver gets lost or chooses a long, out-of-the-way path. Enroute driver information is also beneficial by eliminating the additional energy consumption and emissions associated with driving around, searching for these specific goals. And electronic payment systems eliminate the need for a driver to decelerate the vehicle, idle while a manual transaction takes place, followed by an acceleration that gets the vehicle back up to a desired speed. If this payment can occur without slowing down, emissions and energy consumption are reduced. C. Advanced Transportation Management Systems It is clear that as a roadway network gets increasingly congested due to high travel demand, it is necessary to have good monitoring and management systems: Traffic Monitoring Systems are improving with better
sensor technology and with advances in the information processing. In addition to providing transportation managers with better real-time information, new data processing techniques are being developed to estimate traffic flow, density, and speed. Incident Management is also important in terms of early detection of incidents (i.e., accidents, lane closures, etc.) and swift removal of these incidents so traffic can begin to flow smoothly again. Corridor Management techniques are applicable to freeway networks (e.g., ramp metering) and to signalized arterial networks (e.g., signal synchronization). These techniques are designed to keep traffic flowing as smoothly as possible through the corridor, greatly reducing the amount of idling. Travel Demand Management is another important part of ATMS. Reducing the number of vehicles on a congested roadway through pricing and other techniques can significantly improve traffic flow. All of these ATMS components can have a large impact in reducing energy consumption and emissions. In general, all efforts to keep traffic flowing smoothly at moderate speeds will minimize environmental impacts. Travel demand management goes even further by reducing the number of vehicles in the transportation system, thereby reducing overall energy and emissions. Specific environmental benefits for most of these AVCSS, ATIS, and ATMS implementations have been presented in the literature. For the most part, the quantified benefits are highly dependent on the specific implementation. The benefits of some implementations may be small. However, by implementing many of these technologies simultaneously, significant energy and emission reductions are possible. In the next few sections, we outline several example projects in the fields of AVCSS, ATIS, and ATMS. III. VEHICLE PLATOONING As described in Section II, an automated highway system consists of a variety of AVCSS systems to improve the safety and efficiency of highway travel. In addition, there are several potential environmental benefits: 1) vehicle fuel consumption and emissions will be reduced due to smoother traffic flow (i.e., fewer accelerations/decelerations) and less congestion, resulting in shorter trip times; and 2) if vehicles operate at very close spacings (i.e., platooning, as shown in Fig. 1), the aerodynamic drag on the vehicles will be lower and fuel consumption and emissions will be further reduced. It has been estimated that aerodynamic drag can account for up to 50% of the required energy when traveling at highway speeds. In order to estimate the potential emissions and fuel consumption benefits of an AHS, both simulation and realworld experimentation was carried out as part of the U.S. National Automated Highway System Consortium 1997 Demonstration in San Diego, California [2]. As part of this research, a detailed AHS microsimulation transportation
343
12th IFAC CTS (CTS 2009) Redondo Beach, CA, USA, September 2-4, 2009
model was combined with a comprehensive modal emissions model to predict emissions and energy use for a variety of modeled highways. The predicted AHS emissions and fuel consumption were compared against a variety of scenarios, including: 1) non-automated traffic at different levels of congestion; and 2) idealized traffic flow.
consumption and vehicle emissions, as shown in Fig. 3. These methods combine sophisticated vehicle energy and emission models with route minimization algorithms that are used for navigational purposes. These new methods have been applied to several Southern California case studies resulting in significant energy and emissions savings compared to standard navigation techniques [4].
Fig. 1: Platoon of light-duty vehicles in NAHSC Demo 97 (image courtesy of California PATH Program).
In Fig. 2, fuel consumption per unit distance (given in grams per mile) per vehicle is shown as a function of average vehicle speed for the scenarios of non-automated traffic, ideal constant-speed traffic, and AHS travel. The solid line represents the non-automated traffic scenario, where the data points represent the average fuel consumption for different congestion levels (see [2]). The dashed line represents the ideal constant-speed scenario (i.e., traffic without any acceleration/deceleration events) and could be regarded as the lower limit of emissions for the vehicle at different constant speeds. Results for two AHS scenarios (cooperative and cooperative-platooned) are shown to lie between the ideal minimum and the non-automated traffic under light congestion. The platoon-based AHS showed lower fuel consumption (approximately 5-10%) due to aerodynamic drag reduction when vehicles operate at close spacings. This platooning research has also been conducted with heavy-duty trucks, operating at different spacings [3]. Because trucks have greater aerodynamic effects, greater fuel and carbon dioxide (CO2) savings were achieved, in the range of 10-15%. IV. ENVIRONMENTALLY-FRIENDLY NAVIGATION As an example of ATIS technology, recent research has been conducted in developing navigational systems that specifically target reducing fuel consumption and emissions [4]. Many of today’s navigation systems help guide drivers to their destinations; more sophisticated systems also help drivers avoid congestion on the roadways based on real-time traffic information. These navigation systems have embedded algorithms that attempt to minimize trip distance and/or travel time. By taking this one step further, new navigation techniques have been developed that focus on minimizing energy
Fig. 2: Fuel consumption versus average cycle speed for different AHS scenarios.
In these studies, it was found that in many cases, a timeminimization path also minimizes energy and emissions. However, when congestion occurs, there are cases where this is not true. Because energy and emissions are often higher at congested speeds, a heavily congested (but shorter) path may not be the most environmentally friendly. In contrast, moderate congestion often provides a better choice from an energy and environmental perspective. Moderate congestion generally reduces average traffic speeds from higher free-flow conditions, where vehicles have increased fuel consumption and emissions due to higher loads placed on the vehicle engines. Using historical data of two comparable freeways in the Los Angeles area, it was shown that for almost half of the time, the developed energy/environmentally-friendly navigation system can help a driver choose the best travel route that consumes the least fuel and/or produces the least amount of emissions. This may be highly desirable during the time period when fuel prices continue to hit record high and global warming as well as climate change have become major concerns worldwide. V. DYNAMIC ECO-DRIVING As another strategy to reduce emissions and save fuel, ecodriving is gaining increasing interest worldwide. Eco-driving typically consists of changing a person’s driving behavior based on general static advice to the driver (e.g., do not accelerate too quickly, reduce speeds, etc.). Using ITS technology, it is possible to enhance eco-driving strategies and make it dynamic, where advice is given in real-time to
344
12th IFAC CTS (CTS 2009) Redondo Beach, CA, USA, September 2-4, 2009
drivers based on changing traffic conditions in the vehicle’s vicinity [5]. This dynamic eco-driving strategy takes advantage of real-time traffic sensing and telematics, allowing for a traffic management system to monitor traffic speed, density, and flow and then communicate advice (e.g., recommended speed) in real-time back to the vehicles (as depicted in Fig. 4). By providing dynamic advice to drivers, approximately 10% to 20% in fuel savings and lower CO2 emissions are possible using a simple strategy that smoothes traffic flow during congested conditions without a significant loss of travel time (typically less than 5%) as shown in Table 1. Based on extensive simulation experiments, it was found that in general, higher percentage reductions occur during severe congestion (e.g., LOS E-F) compared to less congested scenarios. Real-world experiments have also been carried out, showing similar reductions but to a slightly smaller degree.
wide range of technology and applications, and most do have an environmental benefit. However, the environmental benefits can be maximized when these ITS applications are “tuned” so that emissions and fuel consumption are specifically reduced. Further, it is important to point out that there will not be a single solution to addressing these environmental issues. Each ITS environmentally-beneficial implementation will likely have improvements in the range of 5% - 15%. However, most solutions are additive, therefore greater benefits can be achieved when a multitude of environmentally-friendly ITS programs are put into place. Instrumented Vehicles
Embedded Road Sensor Data
Traffic Management Center
Traffic Management Center
Traffic Performance Measurement System (PeMS)
Traffic Management Center
Wireless Communications Provider
System Server
Vehicle Data
Internet
Fig. 4: Overall system architecture for real-world experimentation of dynamic eco-driving. Fig. 3: Example snapshot of the environmentally-friendly navigation system showing routes that have lower costs of energy and emissions.
ACKNOWLEDGMENTS The authors would like to acknowledge the University of California’s Energy Institute (UCEI), the University of California Transportation Center (UCTC), the California PATH Program, and the California Department of Transportation for partial sponsorship of this research. The contents of this paper reflect the views of the authors and do not necessarily indicate acceptance by the sponsors.
Table 1: Emissions and fuel consumption differences between non-ecodriving and dynamic eco-driving strategy (from [5]).
Energy/Emissions
Non -ECO
ECO
Difference
CO2 (g)
5439
4781
-12%
CO (g)
97.01
50.47
-48%
HC (g)
3.20
1.90
-41%
NOx (g)
6.28
3.97
-37%
Fuel (g)
1766
1534
-13%
REFERENCES [1]
VI. SUMMARY The goal of this paper is to highlight specific ITS programs that are environmentally beneficial, spanning the three main areas of ITS, including Advanced Vehicle Control and Safety Systems, Advanced Transportation Information Systems, and Advanced Transportation Management Systems. Although these ITS programs have been targeted at improving safety and reducing congestion, it can also be very beneficial for reducing fuel consumption and lowering emissions from transportation. ITS technology consists of a
ITS America, “National Intelligent Transportation Systems Program Plan”, technical report, Intelligent Transportation Society of America, Washington, D.C., see http://www.itsa.org”, 2002. [2] M. Barth, “An emissions and energy comparison between a simulated automated highway system and current traffic conditions”, Proceedings of the 2000 IEEE Intelligent Transportation Systems Conference, Dearborn, MI, Oct. 2000. [3] Browand, F., J. McArthur, and C. Radovich, “Fuel Saving Achieved in the Field Test of Two Tandem Trucks”, California PATH Research Report, report number UCB-ITS-PRR-2004-20, 2004. [4] M. Barth, K. Boriboonsomsin, and A. Vu, “Environmental-friendly navigation,” Proceedings of the 10th International IEEE Conference on Intelligent Transportation Systems, Seattle, WA, September 30 – October 3, 2007. [5] M. Barth and K. Boriboonsomsin, “Energy and Emissions Impacts of a Freeway-Based Dynamic Eco-Driving System”, in press, Transportation Research Part D: Environment, Elsevier Press, 2009.
345