Abstract
Restricting left turns throughout a network improves overall flow capacity by eliminating conflicts between leftturning and throughmoving vehicles. However, doing so requires vehicles to travel longer distances. Implementing leftturn restrictions at only a subset of locations can help balance this tradeoff between increased capacity and longer trips. Unfortunately, identifying exactly where these restrictions should be implemented is a complex problem because of the many configurations that must be considered and interdependencies between leftturn restriction decisions at adjacent intersections. This paper compares three heuristic solution algorithms to identify optimal location of leftturn restrictions at individual intersections in perfect and imperfect grid networks. Scenarios are tested in which restriction decisions are the same for all intersection approaches and only the same for approaches in the same direction. The latter case is particularly complex as it increases the number of potential configurations exponentially. The results suggest all methods tested can be effectively used to solve this problem, although the hybrid method proposed in this paper appears to perform the best under scenarios with larger solution spaces. The proposed framework and procedures can be applied to realistic city networks to identify where leftturn restrictions should be implemented to improve overall network operations. Application of these methods to square grid networks under uniform demand patterns reveal a general pattern in which left turns should be restricted at central intersections that carry larger vehicle flows but allowed otherwise. Such findings can be used as a starting point for where to restrict left turns in more realistic networks.
Original language  English 

Article number  03611981211011647 
Pages (fromto)  452467 
Number of pages  16 
Journal  Transportation Research Record 
Volume  2675 
Issue number  10 
Early online date  13 May 2021 
DOIs  
Publication status  Published  Oct 2021 
MoE publication type  A1 Journal articlerefereed 
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Still waiting at an intersection? Banning certain left turns helps traffic flow
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