Researchers Used a Before-After Analysis to Assess a Dynamic Lane Deployed Using Inside Shoulders near Ann Arbor, Michigan.
Ann Arbor, Michigan, United States
Evaluation of an Active Traffic Management System with Part-Time Use of the Inside Shoulder
Summary Information
Active traffic management (ATM) aims to dynamically manage recurrent and non-recurrent congestion based on prevailing and predicted traffic conditions. Researchers analyzed the effectiveness of the US Route 23 Flex route opened by Michigan Department of Transportation (MDOT) in 2017 to mitigate peak-hour congestion, reduce incident response times, and improve safety. The Flex route uses the corridor’s 11-foot wide inside shoulders as dynamic lanes over a length of 8.5 miles. Researchers analyzed the performance of the Flex route, the safety of the adjusted roadway, driver perceptions, and the costs and benefits provided. Operational performance data was collected using various sources including probe vehicle data, microwave vehicle detection system reports, permanent traffic recorder data, ATM reports, and incident clearance data. Real-world safety data was collected before the lane was installed, from 2012 to 2015, and after, from 2018 to 2019.
Methodology
Changes in average speeds, travel times and various travel time reliability measures along the corridor were quantified using a before-after comparison. Incident clearance and special event data was also collected. Safety performance was evaluated by taking into account before and after data on traffic crashes and volumes as well as roadway characteristics. For the cost-benefit analysis, FHWA's Tool for Operations Benefit Cost Analysis (TOPS-BC) Version 4.0 was utilized to develop monetized values. The capital cost information for the Flex route was obtained from MDOT, and the data for benefit estimation was provided by MDOT and Michigan State Police. User perceptions of the Flex route were collected using a driver survey, a social media analysis of public commentary, and focus groups of adjacent communities and first responders.
Findings
- The overall cost-benefit ratio of the Flex route in both directions was estimated to be between 2.20 and 3.01 depending on the assumptions for service life, which ranged from 10 to 20 years.
- The maximum throughput in the northbound and southbound direction increased by 11.0 percent and 35.4 percent, respectively. During peak periods, travel times decreased on average by 16.5 percent in the southbound direction and by 11.2 percent in the northbound direction.
- The implementation of the flexible lane reduced crashes by approximately 17 percent across the entire corridor, and in the southbound direction, crashes decreased by 34 percent overall and by 50 percent during peak periods. However, crashes increased by 24 percent in the northbound direction during peak periods mainly due to congestion at the northern terminus of the Flex route.
- Of surveyed drivers, 69.9 percent were satisfied or very satisfied with the Flex route. More than half of the drivers (51.9 percent) also reported that the Flex lanes create a safer driving experience when an incident occurs. Drivers also desired the expansion of the Flex lanes and hours of active Flex lane operation.
