Exploring differences in injury severity between occupant groups involved in fatal rear-end crashes: A correlated random parameter logit model with mean heterogeneity

Rear-end crashes are one of the most common crash types. Passenger cars involved in rear-end crashes frequently produce severe outcomes. However, no study investigated the differences in the injury severity of occupant groups when cars are involved as following and leading vehicles in rear-end crashes. Therefore, the focus of this investigation is to compare the key factors affecting the injury severity between the front- and rear-car occupant groups in rear-end crashes. First, data is extracted from the Fatality Analysis Reporting System (FARS) for two types of rear-end crashes from 2017 to 2019, including passenger cars as rear-end and rear-ended vehicles. Significant injury severity difference between front- and rear-car occupant groups is found by conducting likelihood ratio test. Moreover, the front- and rear-car occupant groups are modelled by the correlated random parameter logit model with heterogeneity in means (CRPLHM) and the random parameter logit model with heterogeneity in means (RPLHM), respectively. From the modeling, the significant factors are occupant positions, driver age, overturn, vehicle type, etc. For instance, the driving and front-right positions significantly increase the probability of severe injury when struck by another vehicle. Large truck-strike-car tends to cause severe outcomes compared to car-strike-large truck. This study provides an insightful knowledge of mechanism of occupant injury severity in rear-end crashes, and propose some effective countermeasures to mitigate the crash severity, such as implementing stricter seat belt laws, improving the coverage of the streetlights, strengthening car driver's emergency response ability

Investigating the spatial heterogeneity of factors influencing speeding-related crash severities using correlated random parameter order models with heterogeneity-in-means

Speeding has been acknowledged as a critical determinant in increasing the risk of crashes and their resulting injury severities. This paper demonstrates that severe speeding-related crashes within the state of Pennsylvania have a spatial clustering trend, where four crash datasets are extracted from four hotspot districts. Two log-likelihood ratio (LR) tests were conducted to determine whether speeding-related crashes classified by hotspot districts should be modeled separately. The results suggest that separate modeling is necessary. To capture the unobserved heterogeneity, four correlated random parameter order models with heterogeneity in means are employed to explore the factors contributing to crash severity involving at least one vehicle speeding. Overall, the findings exhibit that some indicators are observed to be spatial instability, including hit pedestrian crashes, head-on crashes, speed limits, work zones, light conditions (dark), rural areas, older drivers, running stop signs, and running red lights. Moreover, drunk driving, exceeding the speed limit, and being unbelted present relative spatial stability in four district models. This paper provides insights into preventing speeding-related crashes and potentially facilitating the development of corresponding crash injury mitigation policies

Function Area Defining of Freeway Ramp

Based on existing research and standards ,this paper proposed a new method of freeway ramp function area calculation, divided the ramp into upstream function area, downstream function area and ramp function area, and redefined each function area. Moreover, according to the relationship among vehicle speed of certain point, the time required to change lanes , design speed and other parameters,modified the time of a lane change in the "Traffic Engineering Handbook", proposed new equation of each area and figure out the length

Safety Assessment of Auxiliary Lanes in Freeway Interchange Weaving Areas based on Traffic Conflict Technique

Auxiliary lanes can provide an improved weaving environment rather than a forced or direct merge or diverse for vehicles entering and departing freeway weaving segments. Considering China's traffic composition and operational status, this paper proposed safety assessment of auxiliary lanes in freeway interchange weaving areas based on traffic conflict technique in order to estimate its safety impacts and related influential factors considered in design. Based on freeway interchange weaving areas data and actual traffic characteristics, simulation models were built with VISSIM. This paper used Surrogate Safety Assessment Model (SSAM) to calculate conflicts by inputting vehicle trajectories from VISSIM, analysed the influence of ramp spacing, lane number of mainline, traffic volume, weaving ratio and percentage of heavy vehicles on safety performance of auxiliary lanes in freeway weaving areas. Finally, Traffic Conflict Modification Factor was presented to evaluate effectiveness of implementing auxiliary lanes. The paper found the safety impacts and related influential factors of auxiliary lanes. T he findings can provide support to effective decision making with regards to constructing future auxiliary lanes in freeway interchange weaving areas

Crash Risk Prediction Modeling Based on the Traffic Conflict Technique and a Microscopic Simulation for Freeway Interchange Merging Areas

This paper evaluates the traffic safety of freeway interchange merging areas based on the traffic conflict technique. The hourly composite risk indexes (HCRI) was defined. By the use of unmanned aerial vehicle (UAV) photography and video processing techniques, the conflict type and severity was judged. Time to collision (TTC) was determined with the traffic conflict evaluation index. Then, the TTC severity threshold was determined. Quantizing the weight of the conflict by direct losses of different severities of freeway traffic accidents, the calculated weight of the HCRI can be obtained. Calibration of the relevant parameters of the micro-simulation simulator VISSIM is conducted by the travel time according to the field data. Variables are placed into orthogonal tables at different levels. On the basis of this table, the trajectory file of every traffic condition is simulated, and then submitted into a surrogate safety assessment model (SSAM), identifying the number of hourly traffic conflicts in the merging area, a statistic of HCRI. Moreover, the multivariate linear regression model was presented and validated to study the relationship between HCRI and the influencing variables. A comparison between the HCRI model and the hourly conflicts ratio (HCR), without weight, shows that the HCRI model fitting degree was obviously higher than the HCR. This will be a reference to design and implement operational planners

Speed-consistency Based Safety Evaluation for Freeway Diverging Segments

Diverging segments are potential bottlenecks because of frequent lane change and deceleration maneuvers. Speed study has been proven to be an effective way to understand the safety performance of diverging segments. This paper addresses the safety level of diverging segments in terms of speed consistency. Speed data is extracted by Tracker based on aerial video imager collected at the diverging segment of MaQun interchange of G42 in Nanjing, China. The operating speed of vehicles is assumed to follow the Linear Regression Model with two explanatory variables—initial velocity and running distance, and the estimated operating speed is amended un der actual traffic conditions. Furthermore, average speed, speed difference and the coefficient of variation are used as safety indicators to establish the speed evaluation criteria. Last but not the least, based on vague set of material-units, the safety level of diverging segments in terms of the velocity arrives at level III, which means that consideration must be given about the safety of diverging segments. The proposed methodology can be used to estimate the safety of diverging segments

Speed-consistency Based Safety Evaluation for Freeway Diverging Segments

Diverging segments are potential bottlenecks because of frequent lane change and deceleration maneuvers. Speed study has been proven to be an effective way to understand the safety performance of diverging segments. This paper addresses the safety level of diverging segments in terms of speed consistency. Speed data is extracted by Tracker based on aerial video imager collected at the diverging segment of MaQun interchange of G42 in Nanjing, China. The operating speed of vehicles is assumed to follow the Linear Regression Model with two explanatory variables—initial velocity and running distance, and the estimated operating speed is amended un der actual traffic conditions. Furthermore, average speed, speed difference and the coefficient of variation are used as safety indicators to establish the speed evaluation criteria. Last but not the least, based on vague set of material-units, the safety level of diverging segments in terms of the velocity arrives at level III, which means that consideration must be given about the safety of diverging segments. The proposed methodology can be used to estimate the safety of diverging segments

Impacts of Large Vehicles on Traffic Safety in Freeway Interchange Merging Areas and Improvement Measures

In order to work out the characteristics of traffic operation on freeway interchange merging areas under different ratio of large vehicles, aerial photography technique based on unmanned aircraft and other observation device were used to investigate the merge section traffic data firstly. Based on survey data and actual traffic characteristics, the paper then established simulation models with VI SSIM with calibrated car-following and lane changing behaviour models. Next, the paper analysed the influence of traffic volume and acceleration lane length under various traffic compositions to evaluate safety status of interchange merge sections by traffic conflict technique and speed consistency index. Finally, two kinds of safety promotion strategies, speed limit and setting forbidden line, were evaluated and the results indicated these measures can raise safety level by about 10%∼15% under certain conditions, which were determined as the best applicable conditions