Current RTA focus

RTA is pleased with the initial success of North Carolina’s first freeway on-ramp signals to relieve rush hour congestion along  I-540 westbound in northwest Raleigh.

A 2018 NC State interim study report commissioned by NCDOT highlights a significantly reduced average peak period (22 minutes shorter, now 1 hour 9 minutes with on-ramp signals vs. 1 hour 31 minutes previously) and a 5% reduction in congestion along the corridor, with 70% of drivers using 540 and its access roadways experiencing shorter drive times.

RTA supports the I-540 on-ramp signals program and encourages its appropriate expansion on other Triangle area freeways. While on-ramp signals cannot create new capacity, they can help freeways better utilize their inherent capacity, by delaying the onset of congestion and minimizing its duration.


On-ramp signals - San Diego1

About on-ramp signals

“On-ramp signals,” also known as “ramp metering signals,” “ramp meters,” “ramp signals,” or “flow signals,” can help freeways remain free-flowing by regulating the flow of traffic entering the freeway during periods when the freeway mainline approaches congested conditions.

In the absence of freeway on-ramp signals, a long line of waiting vehicles can enter a crowded freeway at once and potentially create a backup on the freeway main lanes. While on-ramp signals cannot absolutely guarantee free-flow travel, they can provide a degree of protection by minimizing or delaying the onset of congestion for that freeway segment.

An on-ramp signal is located on the ramp between the intersecting street and the freeway. When activated, the on-ramp signal alternates between short red and green displays. The intermittent displays of a short red signal throttles the demand at the end of the ramp so that the freeway is better able to accept the entering vehicles and remain free-flowing.

On-ramp signals operate on a part-time basis, with the focus on providing congestion relief during rush hour periods. The vast majority of the day the signals are dark and the on-ramp functions normally.

RampMeteringSignals-FHWA-image-simplifiedOn-ramp signals can preserve freeway flow at a very low cost compared to new construction. With traffic entering the freeway in a smoother, regulated fashion, everyone can arrive to their destinations sooner, more reliably, and with increased safety.  In addition, the Federal Highway Administration has noted that on-ramp signals can lead to a reduction in fuel consumption and vehicle emissions. Click here for information from Washington State DOT.

Click here for a one-pager on on-ramp signals available for download. See NCDOT’s project page here.


Results of previous independent study of on-ramp signals in Minnesota

Our current success for the I-540 on-ramp signals in Raleigh is very similar to that experienced in Minnesota several years ago. When on-ramp signals were temporarily deactivated on several Minneapolis-St. Paul freeways in response to a Minnesota legislative mandate, an independent study conducted in 2001 found that when on-ramp signals were deactivated:

  • Travel times increased 22%
  • Speeds dropped 7%
  • Travel time reliability decreased 91%
  • Crashes increased 26%, with a variation of 8% to 200% increase depending on crash type
  • Volume served by the freeway reduced 9%

In other words — all of the above delay, reliability, and safety measures were worse without on-ramp signals in place.

Recent successes of RTA and partners

  • Interim study report, released in May 2018 highlights initial success of on-ramp signals on I-540
  • Four 540 westbound ramps identified for on-ramp signals with activation in fall 2017
  • NC General Assembly passed legislation authorizing on-ramp signals (“ramp meters”) in July 2014.
  • NCDOT study of potential locations in Triangle region for on-ramp signals completed in 2014.
  • The I-40 Regional Partnership, coordinated by RTA, provided information from on-ramp signal experts at the June 2012 meeting.


Media coverage examples:  123, 4