Crash Prevention and Safety
This factsheet is based on past evaluation data contained in the ITS Knowledge Resources database at: www.itskrs.its.dot.gov. The database is maintained by the U.S. DOT’s ITS JPO Evaluation Program to support informed decision making regarding ITS investments by tracking the effectiveness of deployed ITS. The factsheet presents benefits, costs and lessons learned from past evaluations of ITS projects.
A major goal of the ITS program is to improve safety and reduce risk for road users including pedestrians, cyclists, operators, and occupants of all vehicles who travel along our roadways. After many years of declining motor vehicle crashes and fatalities on the Nation’s roadways, reaching a low of 29,867 in 2011, fatalities have slowly started to creep upward, although the number of fatalities per hundred million vehicle miles of travel (VMT) has remained relatively constant. Traffic fatalities for 2016 totaled 37,461, an increase of about six percent compared to the year prior. 
Crash prevention and safety systems detect unsafe conditions and provide warnings to travelers to take action to avoid crashes. These systems provide alerts for traffic approaching dangerous curves, off ramps, restricted overpasses, highway-rail crossings, high-volume intersections, work zones, adverse weather conditions, and also provide warnings of the presence of pedestrians, bicyclists, and even animals on the roadway. Crash prevention and safety systems typically employ sensors to monitor the speed and characteristics of approaching vehicles and frequently also include environmental sensors to monitor roadway conditions and visibility. These systems may be either permanent or temporary. Some systems provide a general warning of the recommended speed for prevailing roadway conditions. Other systems provide a specific warning by considering specific vehicle characteristics (truck or car) and a calculation of the recommended speed for the particular vehicle based on conditions. In some cases, manual systems are employed, where pedestrians or bicyclists manually set the system to provide warnings of their presence to travelers; however these systems are being replaced with automated systems with the increasing implementation of connected vehicle technologies. With the introduction of connected vehicle safety applications, crash prevention and safety systems are also moving from passive driver warning systems, to active driver assistance systems where the vehicle can automatically react to other vehicles or road sensors during hazardous conditions.
Intersection Collision Warning Systems: Intersection collision warning systems use sensors to monitor traffic approaching dangerous intersections and warn vehicles of approaching cross traffic, using roadside infrastructure, in-vehicle systems, or some combination of the two. The newer approaches to intersection collision warning systems provide information to drivers on proper maneuvers (gap acceptance assistance) and warn drivers of right-of-way violations at intersections. The warnings may include the driver’s vehicle violating traffic control signs or signals or of another vehicle violating, or about to violate, the subject vehicle’s right-of-way. Specific examples are provided below:
- Left Turn Assist: Warnings given to driver via an in-vehicle system when trying to make a left turn that may be visually blocked by another car or object. Warnings can alert the driver that a left turn should not be attempted.
- Traffic Control Violation Warning: Warnings given to drivers via in-vehicle systems if it is determined the driver may violate a red light or other traffic control device.
- Stop Sign Gap Assist: Information provided to drivers while stopped at a stop sign where only the minor road has stop signs. The driver receives information of any danger to the vehicle proceeding through the intersection from vehicles approaching on the cross street.
Collision Avoidance Systems: To improve the ability of drivers to avoid accidents, vehicle-mounted collision warning systems (CWS) continue to be tested and deployed. These applications use a variety of sensors to monitor the vehicles surroundings and alert the driver of conditions that could lead to a collision. Examples include forward collision warning, obstacle detection systems, rear impact collision warning, “do not pass” warnings, and road departure warning systems.
Collision Notification: In an effort to improve response times and save lives, collision notification systems have been designed to detect and report the location and severity of incidents to agencies and services responsible for coordinating appropriate emergency response actions. These systems can be activated manually (Mayday), or automatically with automatic collision notification (ACN), and advanced systems may transmit information on the type of crash, number of passengers, and the likelihood of injuries.
Crash Prevention and Safety strategies include collision avoidance systems and systems that warn drivers of potential road hazards. These systems have demonstrated success in detecting potential conflicts and warning motorists of crash potential. Evaluations of these systems find reduction in road crashes, injuries and fatalities as summarized in Table 1.
|Collision Avoidance for Passenger Vehicles||A Korean study finds that Automatic Crash Information Notification Systems would reduce freeway fatalities by 11.8 to 18.1 percent. (2013-00864) Electronic Stability Control (ESC) systems can reduce the risk of fatal crashes by 33 percent. (2013-00861)|
|Collision Avoidance for Trucks||Forward collision warning systems have potential to prevent 23.8 percent of crashes involving large trucks. (2012-00811)|
|Collision Avoidance for Transit Vehicles||In a pilot test, bus drivers using in-vehicle collision avoidance warning systems were involved in 72 percent fewer near-miss events than a control group where the warning feature was turned off. (2017-01198)The camera-based system with a regular angle lens reduced 43 percent of blind zones, and wide-angle camera systems were able to entirely eliminate blind zones. (2013-00853)|
|Lane Depature Warning||Crash statistics show that lane departure warning systems have reduced all relevant crashes by 11 percent, and all relevant injury crashes by 21 percent, controlling for driver demographics. (2017-01175)|
|Pedestrian Safety||In Tucson, Arizona, installation of High-Intensity Activated Crosswalk (HAWK) pedestrian beacons showed 69 percent reduction in crashes involving pedestrians. (2013-00848)|
Table 1: Selected Benefits for Crash Prevention and Safety Strategies.
In-vehicle active and passive safety technologies have also shown to provide significant benefits to road users. The most significant findings are that in-vehicle technologies, including automated braking systems, have the ability to significantly reduce the injury and fatalities due to collisions. Table 2 highlights some of these findings.
|Automated Braking System||Light vehicles that automatically activate in-vehicle alerts, seat belt tensioners, and braking systems can reduce fatalities by 3.7 percent. (2013-00833)In-vehicle technologies that use automated braking to prevent rear-end collisions can reduce drivers injured by 19 to 57 percent. (2013-00832)|
|Combined In-vehicle Safety Systems||A literature review of in-vehicle safety systems in the United States and New South Wales, Australia found that active and passive in-vehicle safety technologies are expected to decrease fatalities up to 16 percent. (2013-00827)Forward collision warning (FCW) alone, low-speed autonomous emergency braking (AEB), and FCW combined with AEB that operates at highway speeds reduced rear-end striking crash involvement rates by 27 percent, 43 percent, and 50 percent, respectively. (2017-01177)|
Table 2: Selected Benefits for In-vehicle Safety Technologies.
Figure 1 shows ranges of benefits for select entries in the ITS Knowledge Resource database at: /. Benefits of collision notification and avoidance system include reduction in fatalities and injury to drivers.
Figure 1: Range of Benefits for Crash Avoidance Technologies (Source: ITS Knowledge Resources).
Here, each metric has a number after the text, representing the number of data points used to create the range; no number means only there was only one data point.
Several crash warning systems have also shown significant benefits in reducing overall number of crashes. Figure 2 shows the ranges of these benefits.
Figure 2: Range of Crash Reduction Benefits from Collision Warning Systems (Source: ITS Knowledge Resources).
As connected vehicle technologies are just now being developed and tested, few evaluations are available. However, driver acceptance clinics were conducted at six different cities in the United States to assess how motorists respond to connected vehicle technologies and benefit from in-vehicle alerts and warnings. The preliminary findings showed that 91 percent of volunteer drivers that tested vehicle-to-vehicle (V2V) communications safety features indicated they would like to have these technologies on their personal vehicle (2012-00785).
Additionally, a European study evaluated the potential benefits and costs of V2V and vehicle-to-infrastructure (V2I) technologies. This study concluded that V2V applications can have positive benefit-cost ratios at fleet penetration rates above 6.1 percent, whereas V2I technologies require a greater market share (2013-00842).
The ITS Knowledge Resources database provides a variety of system costs for crash prevention and safety strategies that range from individual in-vehicle collision avoidance systems to estimates of nationwide implementations of connected vehicle environments.
The database includes several recent cost estimates for in-vehicle collision avoidance systems shown in Table 3. Delphi study techniques, using independent estimates from multiple industry experts and multiple rounds to achieve consensus, were used to forecast the estimated costs for future years.
Table 3: System Costs for Crash Prevention Systems.
|In-vehicle collision avoidance systems||Year||System Costs|
|Advanced Emergency Brake System in the UK (2012-00275)||2011||$334 - $1,337|
|Side collision warning system (Blind Spot Warning) (2013-00287)||2010||$760 - $2,000|
|Radar-based Truck Collision Avoidance system (2017-00382)||2014||$2,500 - $4,000|
|Cost to Vehicle Manufacturers for Embedded On-board DSRC equipment (2013-00288)||2017||$175|
|Cost to Vehicle Manufacturers for Embedded On-board DSRC equipment (2013-00288)||2022||$75|
|Cost Added to Base Vehicle Price for DSRC equipment (2013-00288)||2017||$350|
|Cost Added to Base Vehicle Price for DSRC equipment (2013-00288)||2022||$300|
|Aftermarket DSRC equipment (2013-00288)||2017||$200|
|Aftermarket DSRC equipment (2013-00288)||2022||$75|
The ITS Knowledge Resources database identifies several lessons learned from crash prevention strategies. A national evaluation of ITS applications presents new approaches to address distracted driving when designing and developing ITS applications (2013-00651).
- Communicate alerts designed to orient drivers to general traffic conditions ahead, and therefore, make them more attentive to the driving environment to help reduce driver distraction.
- Use "geofencing" as an approach to limiting driver distraction. The geofencing technique attempts to determine which mode the traveler is using in order to allow transit users to continue to receive updates while on the move while preventing them from using the information while driving. It was demonstrated that it is feasible to determine whether a smart phone user is traveling on a transit vehicle versus in a vehicle on a road. Therefore it is possible to provide travel information to smart phone users while minimizing the risk of distraction.
- Continue to explore avenues for advancements in technology to prevent driver distraction as well as instilling a safety culture mindset to support the goal of a change in driver behavior. As in-vehicle technology continues to develop, supporting safe driving habits will continue to be a challenge.
Case Study: Intelligent Dilemma Zone Protection System at High-Speed Intersections (2017-01212)
Drivers’ actions in an intersection’s dilemma zone, the area where the decision to stop at a yellow light or continue through it is not clear-cut, can lead to side-angle and rear-end crashes. In Maryland, researchers developed an intelligent dilemma zone protection system (DZPS) to reducing these crashes by anticipating drivers’ decisions and responding.
The DZPS system was deployed at two high-speed rural intersections (US-40 at Western Maryland Parkway in Hagerstown, MD and MD-213 at Williams/Locust Point Road in Elkton, MD) and has three components: (1) two wide-range sensors to track speeds and locations of all vehicles within the identified dilemma zones; (2) software to predict the response of drivers during the yellow phase and to activate the all-red extension function if needed; and (3) a web-based module for engineers/technicians to monitor the system’s performance from a control center. Field evaluations of the deployed DZPS were conducted about one month after the system activation dates, and real-time system monitoring and performance analysis was carried out with respect to the traffic flow characteristics impacts and the all-red extension activations.
The maximum length of the dilemma zone was reduced by 960 to 670 feet (vehicles traveling at 75 mi/h), a 30 percent reduction, at the intersection of US 40 and Western Maryland Parkway. The total length of dilemma zones weighted by traffic volume in each speed bin (increments of 5 mi/h from 25 mi/h to 75 mi/h), a 40 percent reduction, from 73 feet to 44 feet. Similar reductions were noted at the intersection of MD 213 and Williams/Locust Point Road.
 FARS Encyclopedia. National Highway Traffic Safety Administration Website. https://www-fars.nhtsa.dot.gov/Main/index.aspx. Last Accessed 12 February 2018.
All other data referenced is available through the ITS Knowledge Resources Database, which can be found at https://www.itsknowledgeresources.its.dot.gov.