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.
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.
On-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.
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.