Optimal Spatial Configuration of Left-Turn Restrictions on Urban Grid Networks Using Enumeration and Population-Based Incremental Learning
Murat Bayrak, Pennsylvania State UniversityShow Abstract
Zhengyao Yu, Verizon Wireless
Vikash Gayah, Pennsylvania State University
The treatment of left turns at signalized intersections drives the development of signal phasing and timing plans and also plays an important role in overall traffic network operations. Accommodating left turns allows for the most direct routing but reduces intersection capacity, whereas restricting left turns improves capacity but requires some vehicles to travel longer distances. This paper attempts to determine at which intersections left-turn restrictions should be enacted to maximize a network’s operational performance. Various spatial left-turn restriction configurations are tested on grid networks in a micro-simulation environment. The optimal configuration is determined using either a partial enumeration of potential options or a population-based incremental learning algorithm. The results suggest that left turns should generally be restricted from intersections in the central portion of the network, whereas left turns should be accommodated on the periphery. Doing so helps to provide additional intersection capacity at the locations where it is most necessary, while minimizing the additional travel distance that is incurred due to detours caused by the left-turn restrictions. The results provide insights into how more realistic networks might be managed to improve network efficiency by only enacting left-turn restrictions at a subset of locations.
Comparative Analysis of Access Control Techniques at the Exit Ramp Terminals to Deter Wrong-Way Driving in Different States
Md Atiquzzaman, Johnson, Mirmiran & Thompson, IncShow Abstract
Huaguo Zhou, Auburn University
Although wrong-way driving (WWD) crashes are rare compared with other types of crashes, the severe outcome resulting from these crashes makes them an important traffic safety issue, especially on freeways. The initial point of origin for the majority of WWD crashes are the exit ramp terminals. During 2009–2013, the exit ramp terminals of full diamond and partial cloverleaf interchanges in Alabama experienced considerably higher wrong-way (WW) entries compared with those in Illinois. In this study, a comparative analysis is conducted between these two states to compare the differences in access control techniques and determine the differences that might have caused the relatively higher frequency of WW entries at the exit ramp terminals in Alabama. The comparative analysis revealed that there are comparatively higher usage of certain access control techniques, which has been recommended in the existing design guidelines to deter WWD. The lessons learned from this study can be useful for the state and local transportation agencies to further understand the best practices of access control techniques that might have potential to reduce WWD crashes on freeways.
Safety Impact of Two Types of Median Opening Access Control Treatments at Unsignalized Intersections on Multilane Divided Highways: Case Studies in Alabama
Beijia Zhang, Auburn UniversityShow Abstract
Md Atiquzzaman, Johnson, Mirmiran & Thompson, Inc
Huaguo Zhou, Auburn University
Rod Turochy, Auburn University
The purpose of this study is to assess the safety effect of the two types of median opening access control treatments: (1) stop bars, stop signs and double yellow line and (2) yield lines, yield signs and double yellow line at unsignalized intersections on high-speed ( ≥45mph) multilane divided highways with wide medians (>30ft) in rural or suburban areas. A cross-sectional comparison was conducted between four pairs of unsignalized intersections (with access controls vs. without access controls at the median openings) in the state of Alabama. Video cameras were installed to monitor each intersection during a typical weekday. Two specific movements: minor-road left-turn movement and major-road left-turn movement are significantly affected by the two median opening treatments. The study includes analyzing 8-hours of video for each location to record the number of traffic conflicts, near-crash situations, and left-turn driver behaviors ( defined as understanding right-of-way, whether or not stopping at the median opening, and using two-stage left-turn movements). The results showed that the stop bars at the median opening can reduce the traffic conflict rate by 30% to 60%, and help more drivers to stop or slow down at the wide median openings to make a better judgment of the safe gap. The painted triangular island at the median opening is helpful to separate the left-turn and through movements at the median opening, which can decrease the near-crash rates. The stop and yield lines combined with a double yellow line can also help the left-turn drivers better understand the right-of-way.