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May/June 2002
Safer Roads Thanks to ITS
by Hui Wang, Patrick Hasson, and Mac Lister
Each year, six million crashes occur on our nation's highways, killing more than 41,000 people and injuring approximately 3.4 million others—at a cost of more than $230 billion, according to the National Highway Traffic Safety Administration. Despite these distressing statistics, driving has become safer in recent decades, thanks to public information and education campaigns, standardization of automobile safety features, and improved vehicle crashworthiness and highway design. Crashes and fatalities, however, remain an inevitable and undesirable by-product of transportation.
Intelligent Transportation Systems (ITS) include diverse technologies ranging from information processing and communications to traffic control devices and electronics. These technologies were first introduced as a means of resolving the conflict between increasing travel demand and insufficient transportation infrastructure. As the value of ITS to road safety became increasingly apparent, safety quickly took center stage as a major focus of many ITS systems.
A brief survey of the ITS technologies currently deployed and under development will help demonstrate the value that these applications will have in improving road safety.
Differentiating ITS Technologies
These technologies usually are divided into subsystems according to their application area, such as Metropolitan ITS versus Rural ITS, or the applicable transportation system, such as Arterial Management Systems, Freeway Management Systems, and Transit Management Systems. Because these subsystems include a variety of technologies, focusing on three overarching kinds of ITS technologies may offer a more effective approach to evaluating the safety impacts:
- Infrastructure-based ITS. Systems that depend exclusively on roadside equipment to improve the performance of the transportation system.
- Vehicle-based ITS. Systems that depend exclusively on in-vehicle equipment to improve driver performance.
- Cooperative ITS. Systems that use both roadside and in-vehicle equipment to improve the performance of the transportation system and the driver.
Infrastructure-based ITS
Four types of technologies are included under infrastructure-based ITS, depending on their purpose: roadside traffic management systems, roadside traveler information systems, intersection traffic management systems, and pedestrian protection systems.
Roadside Traffic Management Systems. These technologies are designed to optimize traffic flows, reduce delays for drivers, and control pollution. They also reduce traffic conflict and, possibly, lower levels of driver stress to reduce the likelihood of crashes. The following roadside devices can accomplish these goals:
- Traffic control devices, such as ramp meters or signal systems using advanced traffic control software.
- Compliance-enforcing devices, like video cameras.
- Traffic signal coordination systems.
- Dynamic traffic management, such as using variable message signs to manage traffic by displaying speed limits appropriate for the driving conditions and time of day. These devices have a traveler information function as well and are mentioned in the next technology type also.
- Incident detection and traffic rerouting, using camera images or induction loops to enable faster response and clearing of the roadway, coupled with variable message signs, radio, and other media to redirect traffic onto alternative routes.
- Optimized roadside lighting systems that adjust lighting levels according to the weather and road surface conditions as obtained through sensors.
Roadside Traveler Information Systems. Traveler information systems improve safety by providing real-time driving information and risk warning, enabling the driver to react before a crash occurs. Roadside devices are only part of the entire system. In-vehicle and vehicle-infrastructure cooperative technologies also play an important role in traveler information systems. Roadside devices that contribute to an advanced traveler information system include:
- Variable message signs providing information such as weather, speed, incidents, and available routes.
- Incident detection systems.
- Weather management systems, such as sensors that detect weather conditions, accurate weather-predicting software, and warning devices, including variable message signs or highway advisory radio.
- Road surface condition detection sensors that collect information on sensitive road segments and provide the information to other systems.
Web-based or kiosk-based pre-trip information systems also are available.
Infrastructure-based ITS systems such as roadside warning flashers like this one for red light violations have the potential to provide significant safety benefits sooner than other systems.
Intersection Traffic Management Systems. An intersection traffic management system has three components:
- Intersection collision avoidance (ICA) systems are designed to identify approaching vehicles that have a high probability of violating the red light or stop sign and to warn drivers on the crossing roads so they can avoid a crash. Sensors record the speed and deceleration of individual vehicles to determine those with a very high probability of not stopping or being unable to stop before entering the intersection. Variable message signs, strobe lights, or traffic signals can warn other drivers of the danger.
- Better-protected left turn phasing has long been used in traffic signal programming, but the main application has been to optimize traffic flow. The increasing attention to safety may trigger additional research on protected left turn phasing to address safety needs.
- Traffic signal compliance is enforced through devices such as cameras.
Pedestrian Protection Systems. Creating safer intersections, increasing signal cycle time for pedestrians still in the crosswalk, and improving driver compliance with signals can better protect this vulnerable segment of road users. Technologies include in-pavement lighting, illuminated pushbutton pedestrian signals, and automated detectors.
Vehicle-based ITS
As if straight from a futuristic science fiction movie, vehicle-based ITS products warn drivers of dangerous situations, recommend actions, and even assume partial control of vehicles to avoid collisions. The so-called "intelligent vehicle" is a major component of ITS.
Collision Avoidance Systems. Like high-tech cat whiskers, collision avoidance systems are designed to help a driver gauge proximity to other drivers or objects. These systems target avoidance of several kinds of roadway crashes, such as rear-end collisions, road departure collisions, lane change and merge collisions, and intersection collisions. These systems obtain traffic information such as acceleration, relative speed, and distance from other vehicles through sensors in the vehicle, then analyze the likelihood of a collision, and give the driver warning of a high probability of collision.
Driver Status and Performance Monitoring Systems. Like an attentive copilot, an onboard driver status and performance monitoring system keeps tabs on the driver. Using sensors to monitor driver performance and psychophysical status, the system identifies dangerous driver conditions (e.g., drowsiness) and distractions and then provides an appropriate warning signal.
Vision Enhancement Systems. Reduced visibility is a significant factor in 42 percent of all vehicle crashes. Lighting and weather conditions such as glare, dawn, dusk, dark, artificial light, rain, sleet, snow, and fog can cause reduced visibility. In-vehicle vision enhancement services will likely be introduced through onboard systems that use infrared radiation from pedestrians, animals, and roadside features to give drivers an enhanced view of what's ahead.
Automated Collision Notification Systems. In-vehicle collision notification systems, such as rural mayday systems, send out notification signals automatically when a crash occurs. By reducing the time between the occurrence of a collision and notification of emergency service providers, automated collision notification systems can help emergency responders get to the scene faster and reduce the consequences of a crash.
Vehicle-Infrastructure Cooperative ITS
Most systems discussed so far cannot be isolated as only infrastructure-based or only vehicle-based. The cooperation of these two actually can improve performance and increase the benefits. The deployment timeframe for cooperative systems, however, can be much longer (20 to 30 years) than for vehicle- or infrastructure-based systems.
Driver Information Systems. To enhance driver awareness of traffic conditions, these systems provide traffic and weather information collected by roadside devices. The information is channeled through in-vehicle equipment and roadside information displays.
Vision Enhancement Systems. In addition to in-vehicle vision enhancement devices, improvements to roadway infrastructure, such as infrared reflective lane-edge marking, can improve a driver's vision.
Intelligent Speed Control System. This system gathers information on the current speed limit from a roadside speed control system and then provides the information through in-vehicle devices and warns the driver of a speed violation.
Collision Avoidance Systems. Combining the power of the in-vehicle driving assistance, roadside detectors, and warning systems that were discussed earlier can make collision avoidance systems more efficient and reliable.
Highway-Rail Intersection Management System. Although highway-rail intersection crashes account for a small percentage of total crashes, the consequences of such crashes usually are severe, if not catastrophic. Systems designed to manage ITS deployment at highway-rail intersections are designed to improve passive crossings and reduce collisions between automobiles and railcars.
- Train-detecting sensors located at highway-rail intersections can detect oncoming trains and warn drivers via variable message signs.
- Gate running accounts for 22 percent of crashes and 26 percent of fatalities; second train warning signs and law enforcement surveillance detectors can deter drivers from entering an intersection when a train is approaching.
- Highway congestion is a major factor in gate running, so traffic management systems can play an important role in reducing highway-rail crashes.
- In-vehicle information devices also can improve driver awareness of highway-rail intersections. Large trucks, transit vehicles, and school buses equipped with these devices are serving as pioneers in several pilot projects.
In-vehicle warning systems that are triggered by roadside devices such as this one for a railroad crossing may provide another level of security for the driving public.
Commercial Vehicle-Related Technologies. Crashes involving trucks and buses usually are more severe than those involving single passenger cars. Commercial vehicles are different from passenger cars in equipment characteristics, performance, and safety requirements. In addition to the more common ITS applications, such as collision avoidance and driver status monitors, special technologies are needed to improve the safety of commercial vehicles. Technologies specifically designed for commercial vehicles include systems to enhance vehicle stability, vehicle inspection systems, onboard recorders, and rear warning systems.
Law Enforcement. Traffic law violations, such as running traffic signals or exceeding speed limits, are among the primary causes of automobile accidents. This type of behavior may be reduced through roadside surveillance devices, such as red light cameras, roadside speed inspection devices, and onboard automatic vehicle control systems, that can take over part of the driving tasks before a crash occurs.
Emergency Service Assistance Systems. Traffic information and route guidance to emergency services can reduce the time between the occurrence of crashes and the arrival of emergency services, thus decreasing the severity of the consequences of a crash. With the help of onboard GPS systems, roadside traffic management systems can give priority to emergency vehicles, therefore reducing their arrival time.
Video surveillance technologies such as this one showing vehicles passing a black ice warning flasher can provide improved warnings and advice to drivers and, when monitored in traffic centers, offer more rapid emergency response and incident management.
Technologies Not Targeting Road Safety
Some technologies have recognizable positive (safety-improving) or negative (safety-detracting) impacts on road safety.
Navigation Systems. From digital maps to street-by-street driving directions, onboard navigation systems already are available to move drivers from point A to point B more quickly and efficiently. Improved navigation can reduce unnecessary travel times and distances, which in turn reduces the risk of crashes. The distraction of fiddling with the device while driving, however, represents a threat to safety. Researchers need to evaluate carefully the safety impact of these devices.
Driver Information Systems. Although traffic information is essential to improving highway safety, redundant or unnecessary signs can needlessly distract drivers. Research on whether the display of information is safe or simply a distraction is needed.
Office-on-Wheels. The market is introducing various office devices into vehicles, such as cell phones, faxes, laptops, and onboard computers. The so-called "office-on-wheels" is designed to make use of driving time, which is usually considered as wasted. These devices can pose a severe safety risk to drivers by distracting them from the main task—driving. Use of cell phones in vehicles, for instance, reportedly has contributed to a significant number of roadway crashes. Because studies of the impact of these devices on road safety have not reached agreement, more research is needed.
Entertainment Devices. Onboard televisions, designed to make driving time more fun, can be another source of driver distraction.
Safety Evaluation of ITS
Evaluations are critical to ensuring progress toward an integrated ITS and achieving deployment of these technologies. Evaluations also are essential to understanding the value, effectiveness, and impact of broader ITS activities, while allowing for the program's continual refinement.
Ramp traffic signals help optimize traffic flow and also have been shown to reduce crashes.
ITS can affect three main variables in road safety: exposure in traffic, risk of crash at a given exposure, and the consequences of a crash. ITS may affect these factors in a number of ways. Telematics and Intelligent Transport Applications for Road Safety, a report by the European Transport Safety Council, summarizes the impacts:
- Direct in-vehicle modification of the driving task by giving information, advice, and assistance, or taking over part of the task. These modifications may influence driver attention, mental load, and decisions about actions such as choice of speed.
- Direct influence by roadside systems providing information and advice, such as guidance on change of route choice.
- Indirect modification of user behavior. This modification often will not appear immediately after a change but may show up after a period of behavioral adaptation. A driver who has an onboard automatic collision avoidance system may tend to drive more aggressively, assuming that the device is protecting the vehicle and passengers.
- Indirect modification of non-user behavior. Non-equipped road users may imitate the behavior of equipped users, following closer or driving faster than they should.
- Modification of interaction between users and non-users. ITS will change communication between equipped users and non-equipped users such as pedestrians.
- Modification of accident consequences by intelligent injury-reducing systems in vehicles, quick and accurate crash reporting, and reduced rescue time.
These impacts help reveal the challenges ITS technologies present. Road safety usually is defined in a negative way; safe road traffic is characterized by the absence of crashes, injuries, and fatalities. Improving road safety naturally is translated as reducing crashes, injuries, and fatalities. Unfortunately, these crash-based measures have a fairly low reliability since crashes are statistically rare events. To be evaluated accurately, ITS requires large-scale implementation in traffic and long periods of exposure. Statistics cannot be collected until systems have been on the road for a long period of time, but safety must be assessed before systems are marketed. The gradual market penetration of ITS also can modify road user behavior in a way that is difficult to study at an early stage of technology deployment. Continuous modification therefore may be required to achieve the optimum benefits of ITS.
Violent, life-ending crashes such as this can be avoided with appropriate technologies.
Another approach for measuring the safety impact of ITS is the use of performance indicators, such as conflicts, exposure, speed, wearing of personal protection, and other measurements that have no direct relation to crashes, but have a known correlation with direct road safety measures. These measures have a comparatively high reliability, but a lower or unknown validity since they are not directly measuring crashes. Decision-makers tend to trust direct road safety indicators more than indirect measures.
Different laboratory, simulation, and statistical methods, as well as real-world tests and follow-up studies after initial deployment, are employed in the safety evaluation of ITS. The follow-up studies are especially important, for they enable quick identification of any safety problem, response, and appropriate adjustment to systems and standards.
Evaluation Results
The need for further development of evaluation methods and tools does not mean that knowledge and experience in this area are insufficient. Numerous studies have shown an overall safety improvement due to ITS technologies. Data from FHWA's ITS Handbook 2000 show some of the safety benefits from operational tests in the United States on various ITS products and services.
These technologies have the potential to affect road safety profoundly. To achieve the greatest safety, pilot projects must be implemented to evaluate benefits and costs. Based on the information presented in the FHWA report, fully deployed ITS systems can help eliminate nearly two million crashes, save 6,000 lives, and prevent 560,000 injuries each year. The total savings to society of these improvements could total more than $48 billion. Clearly, achieving these results is still many years into the future. These numbers provide a tremendous incentive, however, to move as aggressively as possible in ITS research and deployment.
Hui Wang is a Ph.D. candidate at the University of Tennessee, majoring in civil/transportation engineering. She worked in FHWA's Midwestern Resource Center as an intern during the summer of 2001. She also served as a civil/transportation engineer in China's Department of Highway Administration for 6 years. Her specialty is ITS planning and highway design. Wang holds a B.S. in civil engineering from Xi'an Highway Transportation University and an M.S. in civil/transportation engineering with a minor in geography (GIS) from the University of Tennessee. Her current research is devoted to traffic modeling and simulation and ITS-related highway safety. She is a member of the Institute for Transportation Engineers (ITE).
Patrick Hasson is the Safety and Operations team leader in FHWA's Midwestern Resource Center. In this position, he is involved in regional, national, and international projects in the areas of geometric design, Intelligent Transportation Systems, and safety engineering, education, and enforcement. Hasson and his team provide extensive training, technical assistance, and expert advice to State departments of transportation, local officials, national organizations, and others. He is the national coordinator for the FHWA Stop Red Light Running Program, is actively involved in the intersection safety programs, is chairman of an international Expert Group focused on Safety and Technology and participates in a variety of panels and committees for the National Cooperative Highway Research Program (NCHRP), Transportation Research Board (TRB), and Institute for Transportation Engineers. He spent 2 years in the Road Transport Research Program at the Organization for Economic Cooperation and Development. Prior to these assignments, Hasson worked on a variety of transport projects and programs with FHWA, including extensive activities associated with the transportation impacts of the North American Free Trade Agreement. He holds a BS in engineering from the University of Maryland and an MS in engineering from Cornell University.
Harry (Mac) Lister serves as the ITS specialist in FHWA's Midwestern Resource Center in Olympia Fields, IL. Prior to this position, he served as a program coordinator in the ITS Joint Program Office in Washington. He has been actively involved in ITS projects since 1993 as a project manager implementing ITS systems for the Suburban Mobility Authority for Regional Transportation (SMART) in Detroit, as a consultant to ITS America, and currently in FHWA. He has worked in the field of information systems for more than 30 years, the last 15 of which have been in the transportation industry. He has served on committees for the Michigan Public Transportation Agency, the American Public Transportation Association (APTA), American Association of State Highway Transportation Officials (AASHTO), TRB, ITS America, the National Transit Institute for whom he is a Fellow, and the National Highway Institute (NHI). He has a bachelor's degree from Wayne State University and a master's in business administration from the University of Michigan.
Other Articles in this issue:
Arizona Tackles Work Zone Delays
A Hallmark of Context-Sensitive Design
Safer Roads Thanks to ITS
Do Better Roads Mean More Jobs?
Exciting Opportunity for ITS Work
Benefitting from LTPP—A State's Perspective
