State Study Assessed the Mobility Impacts of Adaptive Signal Control on Two Corridors in Omaha, Nebraska.
Adaptive traffic control (ATC) aims to improve traffic signals’ operational and safety performance by gathering data from detectors, and continuously updating signal timings by optimization. ATC can be programmed with a set of predefined scenarios and used to provide appropriate signal timing based on the present traffic conditions. This study evaluated the effectiveness of ATC for two arterial corridors, namely Dodge Street and 84th street, located in Omaha, Nebraska. The Dodge Street arterial corridor contains nine intersections and the 84th Street arterial corridor contains 22 intersections. Travel time and other variables were analyzed during two stages of ATC implementation (June 2019 - September 2019 and January 2020), an 'off' period in early February 2020, and through September 2020 to assess COVID-19 impacts on ATC operations.
In this study, two methods of data collection were considered. First, GPS travel time runs were conducted twice to eliminate the impact of normal seasonal variations in traffic flow for the Dodge Street corridor. For the 84th Street corridor, travel time data was collected with the number of stops and delay data. Second, Bluetooth data were procured from units furnished by a commercial provider that were mounted along the two corridors. GPS and Bluetooth data were used to perform before-and-after analysis for pre- and post-ATC implementation, as well as to evaluate traffic during strict lockdown (March 16-April 30, 2020), eased lockdown (May 1-June 21, 2020), and minimal restrictions (June 22-September 9, 2020).
In essence, this study revealed that the ACT system could not outperform static timing patterns during recurring traffic demand, although it provided adjustments during atypical conditions (e.g., COVID-related demand changes). In most cases, the travel time increased within 11 percent after the implementation of the ATC technology based on GPS data.
For Dodge Street Corridor, Based on GPS Data:
- This study found that Stage 1 of ATC implementation did not improve traffic signal performance.
- It was found that the Stage 2 ATC implementation led to slight improvements compared to Stage 1. However, travel time was still found to be higher as compared to the base, ‘ATC switched off scenario’. This increase was in most cases within 11 percent.
For 84th Street Corridor, Based on GPS Data:
- In most cases, the travel time increased by up to 11 percent and delays by up to 45 percent after the implementation of the ATC technology, based on the GPS data.
- However, in two of the scenarios (based on direction of travel and time of day), the travel time did reduce by up to 15 percent with a corresponding 33 percent reduction in delays.
For Dodge Street Corridor, Based on Bluetooth Data:
- It was found that, based on the comparison of ‘before’ and Stage 2 ATC implementation conditions, travel time increased by up to 19.1 percent, from 4.8 to 5.72 minutes.
- However, based on the comparison of Stage 2 ATC implementation and the strict lockdown conditions, travel time decreased by up to 14 percent, from 5.72 to 4.92. Similarly, based on the comparison of ‘before’ and the strict lockdown conditions, travel time decreased by up to 12.98 percent during the evening peak on Dodge Street East. These results showed that Omaha’s ATC implementation successfully reduced and adjusted signal cycle length in response to COVID-related demand changes.
For 84th Street Corridor, Based on Bluetooth Data:
- Based on the comparison of ‘before’ and Stage 2 ATC implementation conditions, travel time increased by up to 8.65 percent during midday peak period.
- However, based on the comparison of ‘before’ and the strict lockdown conditions, travel time decreased by up to 12.13 percent during morning peak on 84th Street northbound. This result showed that Omaha’s ATC implementation successfully reduced and adjusted signal cycle length in response to COVID-related demand changes.