VDOT starts variable speed limits on northbound I-95

Read ATSSA’s analysis of variable speed zones in Roadway Safety magazine

The Virginia Department of Transportation (VDOT) takes the first step in activating its variable speed zone along Interstate 95 in the Fredericksburg region today.

New LED signs that can display variable speed limits will be illuminated for the first several days with the 65-70 mph limit to give drivers time to adjust to the presence of the signs, VDOT announced.

The system will be fully activated on June 22, at which point speed limits could be anywhere between 35 mph and 70 mph.

The variable speed zone will operate in a 15-mile stretch of northbound I-95 between Exit 110 (Ladysmith) and Exit 130 (Route 3/Fredericksburg), specifically from mile markers 115 to 130. Speed limits will change based on real-time conditions to help vehicles move more efficiently and safely in an area where frequent traffic tie-ups occur.

ATSSA examined variable speed zones in the Winter 2022 issue of Roadway Safety magazine in an article that analyzed their use in multiple states. The article, “Do They Improve Safety?” reviewed details of how the new VDOT variable speed zone will work and how the zones have been used elsewhere in Virginia and in regions across the country.

The article included the following graphic that explains how the process works in the northbound I-95 project.

The new variable speed zone is a $10 million project funded through the I-95 Corridor Improvement Program and the Innovation and Technology Transportation Fund (ITTF).

VDOT is attempting to reduce traffic problems by having drivers adjust their speed based on real-time traffic conditions as well as delays occurring further north in that stretch of the heavily traveled interstate.

“When we studied the I-95 corridor to identify areas for operational improvements, we found recurring congestion was contributing to crashes and driver delay at this location, especially on weekends and during holidays,” Mena Lockwood, VDOT assistant state traffic engineer, said in a news release about this week’s changes.

“Northbound motorists approaching this area are often surprised by a sudden slowdown in traffic, and brake sharply,” Lockwood said. “By installing this variable speed limit system here, we can lower vehicle speeds before travelers reach the point of congestion. This reduces the risk of crashes and resulting injuries, and it maximizes our ability to keep traffic moving.”

Additional details on the I-95 rollout of the variable speed zone from VDOT:

• Flashing beacons attached to the signs will be activated when speed limits are reduced below the maximum limit. Additional static signs posted on I-95 northbound before mile marker 115 will notify drivers they are entering a variable speed limit corridor.
• Message boards controlled by operators in VDOT’s Traffic Operations Centers will communicate the reason why speed limits are being lowered, such as congestion ahead, weather conditions, or lane closures for crashes, work zones or other incidents. Six new 511Virginia traffic cameras will be installed in the corridor by summer 2022 as part of this project, which will assist with traffic monitoring.

• Speed limits will be reduced by only 10 mph at a time, and will hold at that speed for at least a minute so drivers can reduce speed at a comfortable rate.
• When congestion clears, the speed limits will go up directly to the maximum allowable speed limit.
• Variable speed limits posted on the LED signs are enforceable, just as with any other posted speed limit sign.

 VDOT also explained how the system works: 

• Vehicle detectors installed along I-95 use radar to collect traffic speed and volume data, which is fed into a software program. The program uses an algorithm to recognize when speed limits should be lowered, such as when traffic volumes are heavy and speeds are high. The program then assigns incrementally lower speeds to harmonize traffic flow and reduce the risk of crashes and congestion.
• Vehicle detectors do not identify individual vehicles or gather license plate information. 
• Detection equipment has been operational in the I-95 northbound project corridor since fall 2021. This has allowed the project team to perform advanced system testing and study how seasonal travel patterns and inclement weather affects vehicle speed and congestion.
• Backup power will operate the variable speed limit signs and system for up to 24 hours in the event of power loss, and dual signs have been installed at each location to provide redundancy. If a system component experiences a failure, VDOT's on-call maintenance contractor is required to schedule a repair within 8 hours.
• VDOT already uses variable speed limits on Interstate 77 at Fancy Gap in Carroll County, as well as on the approaches and in the Hampton Roads Bridge-Tunnel and on the Monitor-Merrimac Memorial Bridge-Tunnel.