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Variable Speed Limits (VSL)
Slow Down to Get There Faster

Georgia DOT continues to look for cost-effective, innovative ways to address traffic in the metro Atlanta region. One of the most congested roads in metro Atlanta is the northern half (called the “Top End”) of I-285. The “Top End” is the 36 miles on I-285 within Fulton, Cobb and DeKalb counties, north of the I-20 interchanges. To help relieve congestion and improve safety on that corridor, the Department implemented Variable Speed Limits (VSL) on the Top End of I-285. ​

 

What is VSL?

VSL are speed limits that change based on road, traffic, and weather conditions.  Electronic signs slow down traffic ahead of congestion or bad weather to smooth out flow, diminish stop-and-go conditions and reduce crashes. This low-cost, cutting edge technology alerts drivers in real time to speed changes due to conditions down the road. More consistent speeds improve safety by helping to prevent rear-end and lane-changing collisions due to sudden stops. Our ability to remotely change the speed limit on the corridor is not intended to create speed traps. Rather, the changing speed limits are designed to create safer travel by preventing accidents and stop-and-go conditions.

Speed Limit Will Increase from 55 mph to 65 mph

This new limit will be consistent with a similar increase implemented on SouthSide I 285 last fall. Additionally, the new limit is more consistent with driver expectations and behavior on I-285.


 

 Background

 
TMC Operator

The Department conducted a thorough traffic study of I-285 before deciding to increase the speed limit and implement VSL. Georgia DOT believes I-285 can safely accommodate the increased speed. Experience to-date on the southern section of I-285 supports decision to increase base speed limit on Top End.

Why Implement VSL on Top End?

I-285 Top End carries an average of 50,000 more vehicles (100,000 more in some corridors) than SouthSide I-285 and also has almost twice as many interchanges, there is more traffic, more merging, more weaving, more congestion and a greater risk of crashes.

 

 Overview

 

The base speed limit on I-285 (Top End) within Cobb, DeKalb and Fulton counties, north of the I-20 interchanges will be raised from 55 mph to 65 mph to be consistent with a similar increase implemented on SouthSide I-285 last fall.

How Will It Work?

VSL will allow Georgia DOT to electronically reduce the speed limit in 10-mph increments from 65 mph to a minimum of 35 mph in the event of incidents, heavy congestion or severe weather.

  • Transportation Management Center will monitor the roadway for crashes, breakdowns and heavy congestion. When needed for safety purposes, real time adjustments to reduce the speed limit will be made in and leading up to the affected area using active traffic management software.
  • Overhead changeable message signs will warn motorists of upcoming congestion, giving them ample time to slow down.
  • Once motorists clear congested areas, speed limits are increased to normal speeds.
  • The expectation is that the speed limit will remain 65 mph most of the time.
  • Our ability to remotely change the speed limit on the corridor is not intended to create speed traps. Rather, the changing speed limits are designed to create safer travel by preventing accidents and stop-and-go conditions.
  • 176 electronic speed limit signs in 88 locations (Signs located on outside shoulder and median) approximately ½ mile to 1 ½ miles apart on I-285 Top End .
 

 Implementation

 

Preliminary sign structure construction has begun and will continue through July, followed by a 30-day test of the signage in August and implementation scheduled for September.

 Activity  Timeframe
Lane closures for construction of the VSL system will begin on the northern end of I-285

Late Spring 2014

​Changeable Message Signs and VSL signs will be installed ​Late Spring to Summer, 2014
​VSL sign testing ​August 2014
​VSL operation begins ​September 2014

 

 

 Benefits

 

Motorists
  • Reduce congestion and traffic delays by harmonizing traffic flow and reducing traffic crashes
  • Reduce travel times
  • Reduce crash frequency, severity and the likelihood of secondary crashes by reducing the speed of vehicles as they approach an incident, traffic queue, or stoppage
  • Stabilize and smooth traffic flows (consistent speeds within lanes and between lanes)

Results From VSL Studies

VSL has been implemented in other cities, such as Orlando and Seattle and studies show that:

  • VSL allows travel at a slower, but more consistent speed, as opposed to the constant stop-and-go traffic typical of rush hour conditions.
  • By regulating traffic speed, VSL also helps reduce rear end and lane-change collisions associated with sudden stops at the back of congested areas.
  • This more consistent speed improves safety, saves motorists gas and lessens harmful emissions from idling in stopped traffic.
 

 Examples

 

Variable Speed Limit programs have been in use since 1960 and recently implemented in the following states:

 

Contacts

Georgia DOT wants your feedback. Please send your comments and questions to VSL@dot.ga.gov.