Ramp metering, deployed by installing traffic signals on the on-ramp of a freeway, is a freeway active traffic management (ATM) strategy that is often used to control the frequency of traffic onto the mainline, allowing efficient use of existing freeway capacity. This study examined the post-installation impacts of four on‐ramp signals on the westbound lanes of I‐540 in Wake County, North Carolina, using before‐and‐after traffic data. Analyses were conducted using available data from September 2017 (pre‐on‐ramp signals) and October 1, 2017 – September 30, 2018 (post‐on‐ramp signals). All changes to on‐ramp signal operations, outages, and other variables which may influence regular traffic operations in the first two to three months of operation were documented. A benefit and cost analysis were conducted to forecast the net savings over 10 years. This study also provided tools for North Carolina Department of Transportation (NCDOT) to calibrate North Carolina’s on‐ramp signal evaluation framework and planning models to forecast and evaluate on‐ramp signal outcomes into the future.

Capital and programing costs were based on engineering firm estimates. Future projections were discounted with a three percent discount rate. Maintenance costs included the annual and incremental operations and upkeep costs needed to keep a facility operational and the cost of revising an intersection at the end of its anticipated service life. It is not expected that the facility will need to be replaced until after 10 years. Year 2017 is used as the baseline year. The capital cost, programing and operational investments for the ramp metering systems with signals installed on four ramps are shown below.

Table 1: Total Capital, Programming, and Operational Investments

*Projections are discounted into the future

The capital cost breakdown for individual ramp metering site is shown below:

Table 2: Individual On‐Ramp Signal Capital Costs

The long‐term costs associated with the staff required to support the operations of the I‐540 WB on‐ramp signals are shown below.

Table 3: Staffing Costs for On-Ramp Signal Operations

*Projections are discounted into the future