Crash Risk Assessment of Off-Ramps, Based on the Gaussian Mixture Model Using Video Trajectories

Abstract

The focus of this paper is the crash risk assessment of off-ramps in Xi’an. The time-to-collision (TTC) is used for the measurement and cross-comparison of the crash risk of each location. Five sites from the urban expressway in Xi’an were selected to explore the TTC distribution. An unmanned aerial vehicle and a camera were used to collect traffic flow data for 20 min at each site. The parameters, including speed, deceleration rate, truck percentage, traffic volume, and vehicle trajectories, were extracted from video images. The TTCs were calculated for each vehicle. The Gaussian mixture model (GMM) was proposed to predict the TTC probability density functions (PDFs) and cumulative density functions (CDFs) for five sites. The Kolmogorov–Smirnov (K-S) test indicated that the samples followed the estimated GMM distribution. The relationship between the crash risk level and influencing factors was studied by an ordinal logistic regression model and a naive Bayesian model. The results showed that the naive Bayesian model had an accuracy of 86.71%, while the ordinal logistic regression model had an accuracy of 84.81%. The naive Bayesian model outperformed the ordinal logistic regression model, and it could be applied to the real-time collision warning system.

Study on the Rationality of Lane Imbalance Design in Freeway Diverging Areas

“…The vertical axis S of the Frenet coordinate system is established based on s(y), and the horizontal axis L is established based on the normal vector at the starting point of the vertical axis S. The vehicle position under the Frenet coordinate system is represented by (s, l). Assuming that the vehicle has coordinates (y x , x x ) in the Gaussian plane right-angle coordinate system and the nearest reference point (y r , x r ) from (y x , x x ) on s(x) is found according to Equation (7), the vehicle position (s, l) in Frenet coordinates is calculated by Equation (8) and Equation (9).…”

“…To improve the safety of the exit area, researchers have performed much work on crash models, driving behavior studies and safety evaluation. In particular, crash prediction models can be used to assess the impact of various risk factors on crash rates in freeway diverging areas [6], [7]. By collecting data on drivers driving naturally in the deceleration lane, traffic conflicts are considered to be directly caused by driving behavior [8].…”

“…Considering the low feasibility of expanding the existing infrastructure, traffic control has been proposed and used as an effective method to alleviate freeway exit congestion to improve the capacity of the diverging area [25]. In terms of freeway driver behavior, prohibiting drivers from making lane changes near exit ramps through the use of pavement markings has proven to be an effective measure; however, in some instances, prohibiting lane changes only causes the bottleneck to shift to another upstream location where lane changes are allowed [7]. Analysis of field data on exit ramps has shown that the occurrence of traffic bottlenecks is closely related to the exit ramp queue overflow [26].…”

“…According to lane balance theory, the number of lanes added to an isolated freeway off-ramp should not exceed 1. Therefore, a single-lane exit ramp can meet the lane balance requirements, whether it is direct or parallel, but parallel is safer than direct [7], [32]. With the increasing traffic volume, two-lane exit ramps have become the mainstream means of construction, and three-lane exit ramps have been adopted by some multilane freeways with large amounts of diverging traffic, so the lane balance problem becomes a problem that cannot be ignored.…”

Semi-Automatic Extraction of Geometric Elements of Curved Ramps from Google Earth Images

“…Generally, horizontal curves on highway ramps are designed to provide a smooth and safe transition between straight lines along the road trajectory, allowing the vehicle to safely pass a turn at a gradual rate instead of a sharp cut [2]. Unfortunately, as noticed by the Federal Highway Administration (FHWA) Office of Safety, a large number of serious vehicle crashes occur at interchange ramps of highways even though ramps only represent a small portion of the road network [3].…”