The Benefits and Challenges of Variable Speed Limit Systems

The following are excerpts from an article by Debra Ricker, president of Worksafe Traffic Control Industries

Debra Ricker

A Variable Speed Limit (VSL) system comprises several VSL signs and connected detectors for measuring a traffic situation. VSL shows some speed limits, based on the perceived traffic state adjacent to the sign and the traffic state both upstream and downstream.

Variable speed limits were first launched in the 1960s. In the 1970s, it was introduced as a motorway traffic control system. The system boasts of two major outlooks that are adversely defined.

The two major perspectives in the outlook are defined as follows:

  • Homogenization systems that avert traffic congestion by applying minimized speed limits when traffic flow is in near-capacity to prevent unstable traffic situations.
  • Incident detection systems that enhance safety by enforcing the speed limit instantly in case of incidents, thus, minimizing the possibility of more incidents.

Benefits of Variable Speed Limit Systems

Variable speed limits disposals can regulate traffic and enforce efficiency and safety. Because variable speed limit systems have different formation goals and correlating system design, differing benefits are realized.

Speed homogenization forecasts normally apply basic algorithms from real-time traffic to report safety improvements and natural road conditions.

Projects that involve Active Traffic Management (ATM) systems relay practical mobility data for the safety of workers and motorists.

Benefits of VSL systems:

1. Provide Safer Speeds in Work Zones

VSL systems enforce the speed limit of vehicles approaching work zone areas, thus cars pass through at safe speeds.

2. Seamless Traffic Flow and Minimal Delays

VSL units manage vehicles’ speeds to enhance traffic flow and promote safety. VSL promotes traffic flow by applying vehicles’ speed limit when there is an ongoing road construction ahead. It also makes it easy for cars to change lanes by running speed distribution across lanes.

3. Capability to Relate to Road Weather Information Systems (RWIS) to Minimize Speeds during Cold Climate

VSL units can process weather information for the benefit of the road user. Due to this, many agencies install VSL systems.

VSL Units Key Challenges

Implementing a VSL system is no easy task and comes with challenges, such as the enforcement of varying speeds, setting of speed limits, and driver comprehension of the system.

There are various systems installed across the country, and they can be different and unique, with divergent characteristics and performance. Some of the challenges experienced by states in the running of these units include recruitment of experienced staff with broad capabilities to manage VSL systems, maintenance of reliable and nationwide communication, coming up with methods that encourage compliance to VSL signs, generating public consent via outreach activities, lack of valuable data to hold- up VSL system rationale, VSL hardware and software failures, and lag in data that results in delayed information for setting road speed limits.