Delay at an intersection? Implementing prohibitions on certain left turns facilitates smoother traffic movement
Associate Professor Vikash Gayah of Penn State's civil engineering department has developed a new method to identify busy intersections where left-turn restrictions could improve traffic flow. This innovative approach, published in the journal Transportation Research Record, combines two existing heuristic algorithms: a population-based incremental learning (PBIL) algorithm and a Bayesian optimization algorithm.
The hybrid method, as it's called, was found to lead to more efficient traffic patterns than a layout with zero restrictions in simulated scenarios. In more realistic simulations, the hybrid method proved to be the most effective among the three methods (PBIL, Bayesian optimization, and hybrid).
The PBIL algorithm randomly samples potential configurations and recognizes patterns of high-performing options. Meanwhile, the Bayesian optimization algorithm analyzes this new set of high performers to identify how restrictions are affecting traffic at adjacent intersections.
The new method was applied to a generalized network, but the results can be used as a starting point for real-world traffic patterns with the algorithms being customizable on a city-by-city basis. For urban planners, determining where to place the restrictions is a balancing act between intersection productivity and increased travel lengths.
Eliminating left turns could lead to safer intersections, as left turns are where severe crashes, especially involving pedestrians, often occur. By selectively restricting left turns, drivers may need to find alternate routes in certain areas, which could result in traveling a few extra blocks. However, the benefits of reduced traffic bottlenecks and improved overall efficiency could outweigh the minor inconvenience.
The research was supported by a National Science Foundation CAREER award. The postdoctoral researcher Murat Bayrak from the Department of Civil Engineering at Aalto University contributed to the project. The journal for this publication is Transportation Research Record Journal of the Transportation Research Board.
It's important to note that there is no publicly available information about cities that have applied Gayah's method for improving traffic flow at left-turn exits. The grid network, as stated by Gayah, is the most generalizable and not specific to any city.
The DOI for the published article is 10.1177/03611981211011647. For those interested in reading more about this innovative traffic flow solution, this DOI provides direct access to the article.
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