Institute for Transportation

About the research

The goal of this project was to quantify the mobility and safety impacts of different combinations of lane width and shy distance to a barrier for a given paved width. The research team developed a device to measure lateral distance and derive speed, vehicle length/type, and headway information under day and night conditions. Data collected at 17 locations in Illinois, Michigan, and Wisconsin were used for the analyses. Lateral distance data of over a quarter of a million vehicles were used for the safety analysis. Extreme value theory (EVT) modeling was conducted to estimate the probabilities of right edge line encroachment and right barrier contact. Wider lanes were found to have decreased edge line encroachment and barrier contact, while wider shy distances were associated with increased edge line encroachment and decreased barrier contact. The speeds of over 125,000 free flow vehicles were used to quantify the mobility impact. Linear regression modeling was conducted to develop models for estimating free flow speeds in work zones. Work zone free flow speed increases with an increase in speed limit, lane width, and left/right shy distances to a barrier. A case study of a 55 mph posted work zone with two open lanes and barriers on both sides with an available paved width of 26 ft is presented. The results indicate that 11 ft lanes with 2 ft shy distances have a slightly lower probability of right barrier contact (for vehicles in the right lane) than 12 ft lanes with 1 ft shy distances while having a greater free flow speed. This research demonstrates how lateral distance can be collected and modeled along with speed data to assess safety and mobility impacts in work zones. Limitations of the study are acknowledged, and recommendations for future research are presented.