When combined, ramp metering and variable speed limits may reduce conflicts by 16.5 percent and crash odds by 6.0 percent in weaving segments.

Testing and evaluating ramp metering, variable speed limits, and both strategies combined to address weaving segments on freeways.

January 2017

Summary Information

In weaving segments traffic merges, diverges, and weaves in a limit space. These maneuvers can result in high crash hazards. Seeking to address this issue, this study tested Active Traffic Management (ATM) strategies with microsimulation. The strategies tested were ramp metering (RM), variable speed limits (VSL), and an integrated RM and VSL system.


A real-time safety analysis was first conducted by developing a logistic regression model to quantify the impacts of contributing factors to the crash occurrences. It was tested with 16 weaving segments of the East-West Expressway (SR 408) in Central Florida with 21 months of data between July 2013 and April 2015. The ATM strategies were tested on a weaving segment of SR 408, between milepost 12.6 and 13.0. The RM algorithm is a modified ALINEA, which was based on road occupancy and the crash risk of the studied weaving section. Application of VSLs in simulation required changing the desired speed distributions. These strategies were also combined for a set of trials.


Overall, the results showed that these ATM strategies could improve the safety of the weaving segment. The combined RM-VSL strategy reduced conflicts by 16.8 percent and decreased crash odds by 6.0 percent.

Independently, RM with the modified ALINEA strategy improved safety but had a longer travel time than the base case or even a traditional ALINEA strategy. VSL set 45 mi/h upstream of the weaving section also improved safety, but driver compliance is an issue with this strategy.

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Implementation of Active Traffic Management Strategies for Safety of a Congested Expressway Weaving Segment

Author: Wang, Ling; Abdel-Aty, Mohamed; and Lee, Jaeyoung

Published By: Transportation Research Board

Source Date: January 2017


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Goal Areas



weaving segment, ramp metering, variable speed limit, traffic metering, traffic management

Benefit ID: 2018-01253