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.
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
The first on-ramp signals in North Carolina will be installed 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)
NCDOT expects construction to begin in fall 2016 and that the on-ramp signals will be operational by September 2017.
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 Measure||Location and Result|
|Travel time||Atlanta – 10 percent decrease in peak period|
Houston – 22 percent decrease in peak period
Arlington – 10 percent decrease in peak period
|Travel speed||Milwaukee – 35 percent increase in peak period|
Portland – 155 percent increase in peak period
Detroit – 8 percent increase
|Crash rate||Phoenix – 16 percent decrease during metered hours|
Milwaukee – 15 percent decrease in peak period
|Crash frequency||Portland – 43 percent decrease|
Sacramento – 50 percent decrease
Los Angeles – 20 percent decrease
|Driver hours||Sacramento – 50 percent decrease|
|Vehicle volume||Milwaukee – 22 percent increase in peak period|
Sacramento – 5 percent increase in peak period
Detroit – 14 percent increase in volume
|Gallons of fuel saved||Portland – 700 gallons per weekday|
|Emissions reduction||Minneapolis – 1,160 tons annually|
|Benefit-cost ratio||Atlanta – 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.