Project Name

Evaluation of the Safety Effects of the I-77 Active Traffic and Safety Management System

Research Team

Michael Fontaine, Emily Parkany, Katie McCann


Virginia Center for Transportation Innovation and Research

Project Dates

8/1/14 to 5/31/16

Project Description

An Active Traffic and Safety Management System is currently expected to be activated during the summer of 2015 on approximately 12 miles of I-77 north from the North Carolina/Virginia line.  A key feature of this system is that it will contain variable speed limits (VSLs) which will change the posted speed based on current weather conditions, including fog, high winds, snow, and ice.  This location is prone to very severe fog events, and a number of large multi-vehicle crashes have occurred at the site during fog due to drivers traveling too fast for conditions.  Although VSLs have been deployed in other states in an attempt to provide better guidance on safe speeds during fog, relatively few quantitative results are available on their effectiveness.  In addition to providing guidance on safe speeds during adverse weather, the I-77 VSL system may also be used to reduce speeds during incidents and work zones.  The lack of quantitative data on fog VSL systems creates a need for VDOT to perform a robust evaluation of the I-77 system.

This work plan describes a proposed project to evaluate the effectiveness of the I-77 system.  The impact of the system on crashes, mean speed, speed variance, and speed compliance will all be examined.  Impacts of the system during varying severities of weather events will be examined, and effectiveness at different locations along the corridor will be assessed.  Particular emphasis will be placed on examining the system’s impact on large trucks since many of the severe multi-vehicle crashes in the corridor have involved large trucks traveling down steep grades.  The effect of the system when speeds are reduced for incidents and work zones will also be examined.  The results of this analysis will show the effects of the system, and could potentially be used to provide justification for future deployments of weather VSLs elsewhere in the state.  The final report will document the results of the crash and safety surrogate analysis, as well as impressions from the traffic operations center operators and first responders.