Researchers Used Before and After Operational Data and Surveys to Analyze a Dynamic Lane 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.
- Terminate the Flex lane into a deceleration lane or at a system interchange to optimize performance, safety, and perceptions. This study provided ample evidence that corridors ending with a lane drop can negatively affect operations and safety, and led to negative public perceptions. Operational advantages can also be gained if the Flex lane starts near an entry ramp or the conclusion of an acceleration lane to provide a smooth transition. If a lane drop is unavoidable, install additional cameras at both ends of the flex lanes to aid in monitoring incidents at these locations.
- Provide messages on gantries to drivers about lane configuration changes further upstream. Focus groups from this study suggested to ideally allow one mile distance between the merging point and the first merging sign for use of the shoulder.
- Set the advisory speeds at the prevailing speed limit or leave it blank for the Flex lane. Findings from the driver survey and focus groups suggest that the yellow "X" Sign may create significant confusion. Drivers in the study also found the meaning of the advisory speeds could be confusing. Drivers also suggested to display safety messages on signage when an incident occurs.
- Monitor the Flex lanes constantly as travel demands can shift after new Flex lanes go into operation. Shifts in peak demand hours may occur after the introduction of a Flex lane. Implementing a new Flex lane can be context-specific and constant monitoring can help the agency to better adapt to these changes.
