Congestion along North Carolina's freeways is growing, especially during peak travel times, such as morning and evening commute times. While traffic volumes increase, the amount of available funding and physical space limit the N.C. Department of Transportation's ability to widen existing highways and build new ones.

NCDOT, however, can optimize traffic flow on freeways by using technologies such as on-ramp signals, which are a cost-effective and proven way to reduce travel times on the freeway and make them more reliable.

On-Ramp Signal Basics

Also known as ramp meters, on-ramp signals are generally used during peak travel times (e.g., morning and evening commutes) but can be activated any time in response to special circumstances affecting traffic flow - such as special events, wrecks or construction.

Benefits of on-ramp signals include:

  • Smoother traffic flow, which means a more reliable freeway travel times
  • Smoother merges, which means improved safety and fewer crashes

How On-Ramp Signals Work

On-ramp signals are stop-and-go signals on freeway entrance ramps that work just like traffic signals commonly used on roadways.

On-ramp signals

When they are activated, vehicles on the ramp must stop when the signal is red and wait until it turns green before proceeding to the freeway. Only one or two vehicles are allowed to merge at a time, which creates a gap between vehicles and regulates – or meters – vehicles merging onto the freeway.

On-Ramp Signal Locations

Ramp Meter Single Lane One Vehicle Rendering

The first on-ramp signals in North Carolina became operational in September 2017 along westbound Interstate 540 at four ramps in north Raleigh:

  • Falls of Neuse Road (Exit 14)
  • Six Forks Road (Exit 11)
  • Creedmoor Road (Exit 9)
  • Leesville Road (Exit 7)

These sites were selected as pilot sites based on in-depth studies completed in 2013. NCDOT is also evaluating on-ramp signals for Charlotte-area interstates.

Effectiveness of On-Ramp Signals

On-ramp signals were first introduced in Illinois in 1963 on Chicago's Eisenhower Expressway. Several other states – including California, Minnesota, Washington, Arizona and Nevada – use them to effectively keep freeway traffic moving. They also are used extensively throughout Europe – most notably in England, France, Belgium, Germany and the Netherlands.

The following table shows data from other U.S. cities that use on-ramp signals (data based on 2013 studies).

Performance MeasureLocation and Result
Travel timeAtlanta – 10 percent decrease in peak period
Houston – 22 percent decrease in peak period
Arlington – 10 percent decrease in peak period
Travel speedMilwaukee – 35 percent increase in peak period
Portland – 155 percent increase in peak period
Detroit – 8 percent increase
Crash ratePhoenix – 16 percent decrease during metered hours
Milwaukee – 15 percent decrease in peak period
Crash frequencyPortland – 43 percent decrease
Sacramento – 50 percent decrease
Los Angeles – 20 percent decrease
Driver hoursSacramento – 50 percent decrease
Vehicle volumeMilwaukee – 22 percent increase in peak period
Sacramento – 5 percent increase in peak period
Detroit – 14 percent increase in volume
Gallons of fuel savedPortland – 700 gallons per weekday
Emissions reductionMinneapolis – 1,160 tons annually
Benefit-cost ratioAtlanta – benefits were four times greater than the cost after one year and 20 times greater after five years

Frequently Asked Questions

What's the difference between an on-ramp signal and a ramp meter?

An on-ramp signal and a ramp meter are the same thing. North Carolina uses the term on-ramp signal to describe the technology, but federal guidelines require that advanced-warning signs use the term ramp meter.

Do I have to obey the on-ramp signal?

Yes. On-ramp signals are treated and enforced just like traffic signals. Violating an on-ramp signal can result in being ticketed by a law enforcement officer.

How can vehicles merge safely into traffic from a full stop at a signal?

Each signaled ramp is long enough for a vehicle to accelerate to a safe speed before merging into freeway traffic.

How do you keep traffic from backing up onto other streets?

On-ramp signals respond to real-time traffic conditions to balance traffic flow. If vehicles start to back up on the ramp, a sensor will activate the signal to adjust and quickly clear the backup. Traffic cameras will also feed live images to NCDOT's traffic operations center, allowing traffic specialists to manually adjust the signals, if necessary.