Rear-end Collision Risk Research Articles

Development of a Control Strategy of Variable Speed Limits to Reduce Rear-End Collision Risks Near Freeway Recurrent Bottlenecks

The primary objective of this paper was to develop a control strategy of variable speed limits (VSLs) to reduce rear-end collision risks near freeway recurrent bottlenecks. The risks of rear-end collisions were estimated using a crash risk prediction model that is specifically developed for rear-end collisions in freeway bottleneck areas. The effects of the VSL control strategy were evaluated using a cell transmission model. Several control factors were tested, including the start-up threshold of the collision likelihood, the target speed limit, the speed change rate, and the speed difference between adjacent links. A genetic algorithm was used to optimize critical control factors. For the high demand scenario, the proposed control strategy used 25% of the maximum collision likelihood for the start-up threshold, 35 mi/h for the target speed limit, 10 mi/h per 30 s for the speed change rate, and 10 mi/h for the speed difference between different links. For the moderate demand scenario, the strategy used 20% of the maximum collision likelihood for the start-up threshold, 40 mi/h for the target speed limit, 15 mi/h per 30 s for the speed change rate, and 10 mi/h for the speed difference between different links. The results of comparative analyses suggested that the proposed control strategy outperformed other strategies in reducing the rear-end collision risks near freeway recurrent bottlenecks. With the proposed control strategy, the VSL control reduced the rear-end crash potential by 69.84% for the high demand scenario and by 81.81% for the moderate demand scenario.

Surrogate safety measure for evaluating rear-end collision risk related to kinematic waves near freeway recurrent bottlenecks

This study presents a surrogate safety measure for evaluating the rear-end collision risk related to kinematic waves near freeway recurrent bottlenecks using aggregated traffic data from ordinary loop detectors. The attributes of kinematic waves that accompany rear-end collisions and the traffic conditions at detector stations spanning the collision locations were examined to develop the rear-end collision risk index (RCRI). Together with RCRI, standard deviations in occupancy were used to develop a logistic regression model for estimating rear-end collision likelihood near freeway recurrent bottlenecks in real-time. The parameters in the logistic regression models were calibrated using collision data gathered from the 6-mile study site between 2006 and 2007. Findings indicated that an additional unit increase in RCRI results in increasing the odds of rear-end collision by 21.1%, a unit increase in standard deviation of upstream occupancy increases the odds by 19.5%, and a unit increase in standard deviation of downstream occupancy increases the odds by 18.7%. The likelihood of rear-end collisions is highest when the traffic approaching from upstream is near capacity state while downstream traffic is highly congested. The paper also reports on the findings from comparing the predicted number of rear-end collisions at the study site using the proposed model with the observed traffic collision data from 2008. The proposed model's true positive rates were higher than those of existing real-time crash prediction models.

Effects of arousing attention on distracted driver’s following behaviour under uncertainty

This paper proposes issuing alerts to arouse driver attention when the traffic situation ahead is uncertain. Here, "uncertain" means that there exist cues suggesting something is happening in traffic ahead, but it is unclear to the driver and the driver assistance system whether an emergency situation will really occur in the near future, because traffic ahead cannot be seen directly. In such a situation, the driver has to pay attention ahead to prepare a quick response in case an emergency occurs. An experiment with a high-fidelity driving simulator was conducted to investigate the effectiveness of an attention arousing system when the driver was distracted. The results showed that the attention arousing system contributed to increasing time headway (THW) to the lead vehicle, where THW is the headway distance divided by the host vehicle speed and is often used to evaluate the rear-end collision risk. Such safety compensating behaviour was observed not only under distracted conditions, but also under non-distracted conditions. However, the compensating behaviour was not excessive under non-distracted conditions. The attention arousing was effective to maintain safety when the lead vehicle decelerated rapidly. The reaction time was long when the drivers were performing a distracting task. However, because the drivers had increased THW beforehand when conducting the distracting secondary task, the delay in reaction did not worsen the situation.

Effect Analysis of Intermittent Release Measures in Heavy Fog Weather with an Improved CA Model

Heavy fog may easily cause traffic accidents; thus freeway closures are frequently taken in order to ensure traffic safety in China, which not only seriously affect the travel of people, but also bring great economic losses. This paper studies the fog related risk of rear-end collisions and the intermittent release measures taken to reduce such risk; meanwhile, an improved cellular automaton model considering driving behaviors in heavy fog is proposed. The simulation results indicate that the risk indicatorfain fog is much higher than normal weather when cellular occupancyρ<0.5. After taking intermittent release measures, the magnitude offawill drop from 10−4to 10−5under the same fog condition, which greatly enhances the safety. In addition, this paper concludes the appropriate vehicle number released for each time and the time intervalhtbetween adjacent fleets and the maximum number of vehicles𝒬maxwhich can be released per hour. These results can be used as theoretical basis and reference for the traffic management departments to develop intermittent release measures.

Numerical Simulation of Traffic Flow in the Tollgate Area with Variable Speed Limits

We investigate behaviors of vehicles passing a controlled area with variable speed limits (VSL) before a tollgate. The traffic flow mathematical model is formulated based on optimal velocity model. The typical sketch of tollgate area is plotted and variable speed limit signs are set in the area to control the traffic flow speed for fear of accident and congestion. Simulations are carried out to examine the influence on traffic flow passing the controlled area with different number of the speed limit signs under open boundary condition. The simulations results show that more speed limit signs may reduce the risk of rear-end collision and the occurrence of the congestion in the tollgate area.

Effect of Arterial Signal Coordination on Safety

Traffic signals are coordinated to improve traffic mobility, but the impact of coordination, particularly specific coordination solutions, on safety is not well known. Engineers who set coordinated signals can use several tools to improve traffic mobility but have no tool with which to account for safety. A study was done on the impact of arterial signal coordination on the frequency and severity of rear-end and right-angle collisions—the two types of crashes that are both prevalent at signalized intersections and likely affected by signal coordination. Multinomial logit models were developed to estimate crash likelihood in short time intervals on arterial intersection approaches, as well as the severity of crash outcome. The obtained models were used to investigate the safety impact of signal coordination and other road and traffic variables. The following results were determined: (a) signal coordination can significantly affect crash likelihood and severity; the concentration of vehicle arrivals in the second half of a green phase is associated with significantly lower crash likelihood and severity; (b) certain components of the traffic flow are most susceptible to crashes; (c) short distances between intersections and short cycle lengths are associated with a lower risk of crash; and (d) the presence of a right-turn bay is associated with a considerable improvement in safety manifested by a lower risk of rear-end and right-angle collisions. The developed models can be used as a tool for evaluating alternative signal coordination plans for safety.

Combined Effect of Traffic and Geometrics on Rear-End Collision Risk

This paper presents the results of a laboratory experiment that sought to analyze rear-end collision risk under various traffic conditions and given various road geometric configurations. The CRISS (Inter-University Research Center for Road Safety) interactive fixed-base driving simulator was used. An 8–km, two-lane, rural road that incorporated 15 tangents and curves was designed and implemented in the driving simulator. Four distinct traffic conditions were simulated, and 32 drivers drove in four traffic scenarios. The differences in speed and position between each driver's vehicle and other vehicles on the road were collected to calculate two safety indicators, which the scientific literature has suggested to evaluate rear-end collision risk on the basis of the time-to-collision (TTC) notion. The maximum values of these indicators were given for an average traffic-flow condition, which is therefore the most critical condition for rear-end collision risk. In scenarios that entailed lower traffic volumes, significant models of TTC-based indicators were found for tangents with lengths that ranged from 400 m to 1,000 m. The independent significant variables were volume-to-capacity ratio, length of the tangent, and length of the curve approaching the tangent. In traffic scenarios characterized by higher traffic volumes, no significant models were found for any kind of geometric element. This outcome seems to prove that the influence of the geometric features on the rear-end collision risk tends to become negligible whenever the volume-to-capacity ratio reaches high levels. In these conditions driver behavior is exclusively affected by interactions among vehicles.

A Comparison of Tactile, Visual, and Auditory Warnings for Rear-End Collision Prevention in Simulated Driving

This study examined the effectiveness of rear-end collision warnings presented in different sensory modalities as a function of warning timing in a driving simulator. The proliferation of in-vehicle information and entertainment systems threatens driver attention and may increase the risk of rear-end collisions. Collision warning systems have been shown to improve inattentive and/or distracted driver response time (RT) in rear-end collision situations. However, most previous rear-end collision warning research has not directly compared auditory, visual, and tactile warnings. Sixteen participants in a fixed-base driving simulator experienced four warning conditions: no warning, visual, auditory, and tactile. The warnings activated when the time-to-collision (TTC) reached a critical threshold of 3.0 or 5.0 s. Driver RT was captured from a warning below critical threshold to brake initiation. Drivers with a tactile warning had the shortest mean RT. Drivers with a tactile warning had significantly shorter RT than drivers without a warning and had a significant advantage over drivers with visual warnings. Tactile warnings show promise as effective rear-end collision warnings. The results of this study can be applied to the future design and evaluation of automotive warnings designed to reduce rear-end collisions.

Reproduction of Rear-end Collision Risk based on Data Acquired by Drive Video Recorder and Verification of Driver's Brake Operation

Reproduction of Rear-end Collision Risk based on Data Acquired by Drive Video Recorder and Verification of Driver's Brake Operation

The contribution of stereo vision to the control of braking

In this study the contribution of stereo vision to the control of braking in front of a stationary target vehicle was investigated. Participants with normal (StereoN) and weak (StereoW) stereo vision drove a go-cart along a linear track towards a stationary vehicle. They could start braking from a distance of 4, 7, or 10 m from the vehicle. Deceleration patterns were measured by means of a laser. A lack of stereo vision was associated with an earlier onset of braking, but the duration of the braking manoeuvre was similar. During the deceleration, the time of peak deceleration occurred earlier in drivers with weak stereo vision. Stopping distance was greater in those lacking in stereo vision. A lack of stereo vision was associated with a more prudent brake behaviour, in which the driver took into account a larger safety margin. This compensation might be caused either by an unconscious adaptation of the human perceptuo-motor system, or by a systematic underestimation of distance remaining due to the lack of stereo vision. In general, a lack of stereo vision did not seem to increase the risk of rear-end collisions.

Effect of Red Light Cameras on Accident Risk at Intersections

One major cause of accidents at signalized intersections is vehicles running red lights. To discourage red light running (RLR), a number of authorities have installed red light camera (RLC) systems on the approaches to these signalized intersections. There have been indications from several studies that RLCs have been effective in curbing RLR; this leads to potential reduction in right-angle collisions. However, there are also concerns over a possible increase in rear-end collisions. This paper investigates the effect of RLCs on accident risks at signalized intersections for both right-angle collisions and rear-end collisions. A binary logit model was preliminarily developed to examine how the stopping–crossing decision of drivers at the onset of amber is affected by geometric, traffic, and situational variables. Results showed that the presence of RLCs is one of the five significant factors affecting a driver's decision to cross at the onset of amber. A multinomial logit model further confirmed that RLCs are effective in reducing RLR frequency. Further analysis on the fitted models revealed that while the presence of RLCs is effective in reducing risk of right-angle collisions, it has a mixed effect on the risk of rear-end collisions. Whether the RLC reduces or increases the possibility of rear-end collisions depends on the speed of the trailing vehicle and the headway between vehicles.

Evaluation of Collision Warning-Collision Avoidance Systems Using Empirical Driving Data

Collision warning-collision avoidance (CWCA) systems are showing increasing promise in preventing rear-end collisions. The effectiveness of many prototype systems has been evaluated on driving simulators or through numerical simulation, and several field tests are under way. Most investigations have focused on the safety benefits to host vehicles. Possible effects of CWCA-equipped vehicles on other traffic, especially the direct follower, have received little attention. Results of an evaluation study of this issue are presented. It is found that CWCA vehicles may have higher risk of rear-end collision with following vehicles. Thus, it may be necessary to design a CWCA system that is able to offer a balanced protection to host vehicles and to other traffic by considering possible effects of CWCA systems on other traffic.

Evaluation of Collision Warning–Collision Avoidance Systems Using Empirical Driving Data

Collision warning–collision avoidance (CWCA) systems are showing increasing promise in preventing rear-end collisions. The effectiveness of many prototype systems has been evaluated on driving simulators or through numerical simulation, and several field tests are under way. Most investigations have focused on the safety benefits to host vehicles. Possible effects of CWCA-equipped vehicles on other traffic, especially the direct follower, have received little attention. Results of an evaluation study of this issue are presented. It is found that CWCA vehicles may have higher risk of rear-end collision with following vehicles. Thus, it may be necessary to design a CWCA system that is able to offer a balanced protection to host vehicles and to other traffic by considering possible effects of CWCA systems on other traffic.

Traffic Safety Analysis in an Underground Urban Expressway using MOVIC-T4

This paper describes the traffic safety analysis in an underground urban expressway using the motion-base driving simulator MOVIC-T4. First, the deterioration of a driver's awareness level is analyzed. Second, the secondary accident risk of rear-end collision to the accident vehicle is analyzed. In addition, the effectiveness of a simple information system is analyzed under the abovementioned risky traffic situation The results indicated that the deterioration of the driver's awareness level can occur while driving in underground urban expressways for around 10 minutes. An information system to warn the driver of an accident vehicle ahead can prevent a rear-end collision.

A method for identifying rear-end collision risks using inductive loop detectors

An innovative feature of this study is to firstly attempt to capture rear-end collision potentials from the analysis of inductive loop detector data. Signals collected from loops are applied for monitoring individual vehicle information on freeways to estimate safe stopping distances in car-following situations. An index to quantify the potential of rear-end collisions is derived, and further employed for developing criteria to evaluate levels of rear-end collision risks. The proposed methodology based on loop detector data enables to identify collision potentials in real time. It is believed that the index would be a valuable tool for operating agencies in developing various strategies and policies toward enhancements of traffic safety.

DEVELOPMENT OF A RISK EVALUATION MODEL FOR REAR END COLLISIONS CONSIDERING THE VARIABILITY OF REACTION TIME AND SENSITIVITY

A model and a measure that can evaluate the risk of rear end collision are developed considering actual driver's behaviors. These behaviors are analyzed on the basis of three concepts - risk, responded risk, and accident - related to accidents. An index that can represent the risk was also developed based on the methods used in evaluating noise level. For risk comparison among various situations, the equivalent risk level with respect to the intensity and duration time is developed. The model was validated with field surveys of the expressway of Seoul using a test vehicle capable of collecting the traffic flow data. Based on these data, the risk by section, lane, and traffic flow conditions was evaluated and compared with the accident data and traffic conditions. The results showed that evaluated risk level corresponds closely to the patterns of actual traffic conditions and number of accident.

Development of a high-functionality tail lamp system in the second phase of the ASV program

A high-functionality tail lamp system aimed at reducing the risk of rear-end collision was developed and installed on the ASV-2, prototype vehicle produced in the second phase of the Advanced Safety Vehicle program promoted by the Ministry of Land, Infrastructure and Transport of Japan. This paper presents experimental findings concerning basic driver cognition and response behavior in connection with stop lamp illumination and approach to a preceding vehicle. It also describes the main functions of the system comprising an emergency braking advanced advisory and large high-mounted stop lamps.

Road safety engineering: an effective tool in the fight against whiplash injuries

Road safety engineering can play an integral part in the prevention of whiplash injuries. While improvements to vehicle design can reduce the severity of whiplash injuries when a crash occurs, improvements to road safety can prevent whiplash-inducing crashes from occurring in the first place. Whiplash injuries are most commonly associated with rear end crashes. Unfortunately, rear end crashes are also the most common type of crash at urban signalized intersections, where the majority of crashes occur in British Columbia, Canada. The Insurance Corporation of British Columbia (ICBC), through the road improvement program, has been funding road improvements in order to reduce the frequency of collisions at high crash locations in British Columbia. Several road safety engineering countermeasures specifically targeted at rear end collisions have been researched and deployed. These countermeasures include simple and affordable solutions such as signal visibility enhancements, as well as complex and expensive solutions such as intersection geometric upgrades. When appropriately used, these countermeasures have proven to be extremely cost-effective in reducing the frequency of rear end collisions. Widespread application of signal visibility enhancements is now being pursued to further decrease the risk of rear end collisions and whiplash injuries. Costs are the direct cost of the ICBC portion of the investment and benefits are only those associated with reduced insurance claims over a 2-year period.

Risky driving behavior: a consequence of motion adaptation for visually guided motor action.

The authors examined the effect of adaptation to expansion on overtaking maneuvers in a driving simulator. Following driving on a straight empty road for 5 min, drivers initiated overtaking substantially later (220-510 ms) than comparable maneuvers made following viewing a static scene or following 5 min of curve driving. Following adaptation to contraction (produced by driving backward), observers initiated overtaking significantly sooner. The removal of the road texture significantly reduced the size of the adaptation effect. The authors propose that these changes in overtaking behavior are due to misestimation of the time headway produced by local adaptation of looming detectors that signal motion-in-depth for objects near the focus of expansion. This adaptation effect may increase the risk of rear-end collisions during highway driving.

The relationship between an option space and drivers' indecision at signalized intersection approaches

A traffic signal is a substantially different traffic sign compared with other traffic devices. The uniqueness of traffic signals is manifested in their displaying an alternate message, not a constant one. The transition period from one message to another creates a decision problem for drivers. An inappropriate decision might create the risk of a rear-end collision. This article presents a disaggregate behavioral model of drivers' decisions when the green light ends. It is demonstrated, and supported by field data, that a large option zone increases the indecision of drivers, which creates a greater risk of rear-end collisions. The influence on drivers' decisions of distance from the intersection and of approach speed is examined through the model.