On-ramp signals or ramp meters are used to control the number of vehicles allowed to enter a freeway to allow for smoother merging at on-ramps. North Carolina Department of Transportation (NCDOT) commissioned a study to assess the first-year operational impacts of four on‐ramp signals which were installed along Interstate 540 in North Carolina in September 2017. Signals were positioned on the westbound lanes of four on-ramps in Wake County and have been regularly activated Monday to Friday from 6:30 ‐ 9:00 am. Researchers analyzed the impacts to traffic using data collected in the affected area from numerous sources, both before and after the installation of on‐ramp signals. When feasible, the costs and benefits of the on‐ramp signals were monetized using benefit cost analysis methods.
The planning‐level evaluation focused on four major steps:
- planning‐level data collection
- planning level analysis
- life cycle cost analysis
- before‐and after installation evaluation
Key data types included probe and Bluetooth travel time data, on-ramp signal data, radar-based traffic counts, Annual Average Daily Traffic (AADT), traffic monitoring video, operation data and safety data. Researchers conducted before-after analyses comparing the first‐year results following the installation (October 1, 2017 - September 30, 2018) with data from prior to the installation in September 2017. The monetized value of reductions in driving delays was used as the benefit measure.
A comparison of before and after traffic conditions during morning weekday peak hours showed the following benefits in the on-ramp signal corridor (excluding arterial roadways), on average.
Reduced delay benefits:
- The installation of the four on-ramp signals resulted in reduced delays, which were equivalent to $9.6 million in monetized value over 10 years.
- These on-ramp signals are estimated to reduce the vehicle delay for commuters by a total of 13 hours per average daily commuter vehicle over the 10-year analysis period.
- The total annual vehicle-hours of delay for the corridor decreased by approximately 8.5 percent after the installation of on-ramp signals.
- Evaluation results showed a delay savings with a monetized value of $38 per year for the average daily commuter vehicle. A commuter that typically drives the on-ramp signal corridor each weekday is expected to experience reductions in delays with a total monetized value of $369 over 10 years.
Travel time savings:
- Eighty four percent of commuters experienced shorter drive times.
- Drive time per day for a commuter decreased up to two minutes (7.3 percent).
Throughput benefits in reduced congestion and improved handling of traffic volumes:
- There was a 12-minute decrease in the average duration of the daily congested period along the on-ramp signal corridor, excluding arterial roadways. There was a nine percent overall decrease in recurring congestion compared to the period before on-ramp signal installation.
- Evaluation results showed an overall increase in driver volumes on the corridor, indicating that the majority of drivers were not deterred by the on-ramp signals.
Researchers also estimated the long-term costs associated with the staff required to support the operations of the I-540 westbound on-ramp signals. Capital, programming, and operational investments based on NCDOT estimates were included as cost components in order to estimate overall net benefits. The total net monetized mobility benefit over ten years after the installation of the on‐ramp signals was $7,949,541. The findings from the analysis exclude estimations of the cost savings associated with safety benefits, which could not be determined without additional years of data from before and after installation.