Characterizing congestion impact of road diet lane reduction using probe vehicle data

Abstract

As our society continues to promote vehicles as the primary means of travel, pedestrians and bicyclists in local communities tend to be neglected, causing unsafe conditions for those travelers. To combat this, road diets are being implemented which are proving to be a cheap and effective means to increase safety by reducing traffic speeds. A road diet is a general term used to describe the reduction of lanes along an existing roadway with the goal of slowing traffic. This reduction allows for space to be repurposed for other uses, such as expanding shoulders, providing parking, or bike lanes. Research into road diets has shown that they improve safety, however little research behind congestion impacts has happened. In the state of New Jersey, the need for bicycle and pedestrian friendly infrastructure is evident, with 50 road diet projects already completed, and more on the way. The purpose of this study is to analyze road diets in NJ and provide a means of measuring congestion for the upcoming projects in the state by analyzing already existing road diets through performance measures to analyze potential shifts in speed along corridors with a road diet. Anonymous Probe Vehicle speed data was used and was obtained through spatially defined Traffic Message Channels. Road diets with reliable data available and without prolonged external events were analyzed. Based on this criterion two study sites were chosen: Washington Avenue in Green Brook Township and Montgomery Street in Jersey City. Figures are only shown for Washington Avenue. Performance measures used were in the form of speed distribution heat maps, modified vertical box and whisker (BW) plots, and cumulative frequency diagrams. Heat maps would be used to show changes in speed patterns, the BW plots to show changes in distributions during peak hours, and CFDs to show shifts at different percentiles during peak hours. A secondary analysis of crash records was also conducted on Washington Avenue before and after road diet installation. These measures were capable of showing shifts after an event, like one caused by the implementation of a road diet.