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US - 23 Flex Route Project



  1. MDOT developed specialized training for Flex Route Operators as well as eleven Quick Reference Guides.
  2. Along with the Flex Route system, MDOT incorporated other safety innovations and multi-modal opportunities into the project.
  3. The Flex Route improved system reliability and planning time during the peak hour by 56% southbound in the morning and 27% northbound in the evening.


In 2017, the Michigan Department of Transportation (MDOT) opened its fi rst Flex Route along US-23 in Washtenaw and Livingston Counties. For over 20 years, a solution to the problems of peak hour directional traffic, incident management and corridor operations and safety eluded the department. All short-term solutions for congestion, operations, and incident management were exhausted through the implementation of Intelligent Transportation System (ITS) and expansion of a Freeway Courtesy Patrol. However, a long-term solution to adequately address safety, recurring, and non-recurring congestion and incident management was still needed. Due to the state of Michigan’s infrastructure funding challenges and an estimated construction cost of over $185 million to widen the US-23 corridor, MDOT investigated other innovative ways to solve the corridor’s operational and safety problems. The US-23 Flex Route was the solution.

Opened to traffic in December of 2017, the US-23 Flex Route is nine miles in length from M-14 to M-36 north of Ann Arbor. The project included construction of road, bridge, and interchange operational improvements including Active Traffic Management (ATM) strategies for the US-23 corridor to address daily recurring and non-recurring traffic, incident management, and overall motorist safety. Using the Flex Route’s lane control gantry system, MDOT can dynamically manage recurrent and non-recurrent congestion through technology and a perfect combination of ATM strategies, including dynamic lane control and shoulder use, variable speed advisories and queue warning.


In 2009, MDOT completed the US-23 Corridor Feasibility Study which analyzed both traditional and non-traditional improvements such as local system/operational improvements, transit service options, bus bypass shoulders, additional general-purpose lanes, additional High Occupancy Vehicle (HOV) lanes and additional High Occupancy Toll (HOT) lanes. The feasibility study identified the additional general purpose lane alternative as the preferred alternative; however, due to its lack of economic feasibility and the public’s scrutiny and lack of acceptance for additional capacity, a corridor widening alternative was not a feasible option.

In 2014, MDOT initiated the National Environmental Policy Act Environmental Assessment (EA) process to explore five different alternatives to address transportation infrastructure condition needs and directional peak hour traffic congestion of the US‐23 corridor. The alternatives included in the US-23 improvements EA were a No Build, Transportation System Management (TSM), Ramp Metering, ATM with HOV and ATM (which was later branded as the Flex Route).

The Flex Route alternative met the purpose of and need for the project goals better than the other alternatives. It addressed incident management and safety at a higher level than the other alternatives because it allows for the use of the median shoulder to manage traffic during incidents. To ensure project success, MDOT performed detailed analyses and sought innovations and efficiencies during each phase of the project. For example, during planning and design, MDOT used the Metropolitan Planning Organization’s regional travel demand forecasting model and a VISSIM model to predict changes in traffic patterns and analyze the traffic impacts. MDOT also strategized with other states that had ATM systems to gather lessons learned. This information was used to modify the system’s design for the best possible product for the public.

During construction, MDOT design and construction staff met with maintenance staff to discuss ways to improve maintenance response times and efficiencies. After developing maintenance performance measures, the design of the system was modified to include remote access and a rebooting mechanism in each gantry cabinet to improve maintenance response time.

For software development, MDOT performed a risk assessment and analyzed the cost, schedule and quality of different software modules. Once completed, MDOT chose to modify the Virginia DOT’s ATM software module to function with MDOT’s existing Advanced Traffic Management System software. The software includes: response plans for the MDOT Statewide Operations Center (STOC) Flex Route Operators to open the shoulder during peak periods; an algorithm to analyze real-time data and propose advisory speeds to harmonize traffic flow; and logic for dynamic response plans to react to incidents that may require lane closures and/or shoulder openings. To do this, Flex Route operators use Dynamic Message Signs (DMS), Microwave Vehicle Detection Systems (MVDS), Closed Circuit Television (CCTV) cameras and fiber optic cable.

MDOT developed specialized training for Flex Route Operators as well as eleven Quick Reference Guides (QRG). The QRG’s give the operators quick guidance for different operational scenarios such as “Scheduled Shoulder Use,” “Unscheduled Lane Restriction,” and “Winter Maintenance Procedures.”

Along with the Flex Route system, MDOT incorporated other safety innovations and multi-modal opportunities into the project. MDOT added truck parking ITS, seven emergency pull-off sites and a park and ride facility that is enabled with ITS for future transit service.


  • Led and navigated complex federal and state planning processes for the US-23 project including environmental clearance, public and Metropolitan Planning Organization (MPO) involvement, Concept of Operations and traffic modeling. Through the NEPA, Planning, Context Sensitive Solutions (CSS), Design and Construction phases, MDOT held over 100 agency, stakeholder and public involvement meetings including presentations to explain the concept, obtained input and feedback and provided education.
  • Branded the US-23 project as the US-23 Flex Route and created project videos to explain the overall project and the system. MDOT shared these videos locally, regionally, and statewide.
  • Developed an education and communication plan and spent over a year generating exposure and presenting Flex Route information to the public and local governmental agencies and stakeholders.
  • Created where MDOT shared instructional videos and project information, answered frequently asked questions, provided a monthly newsletter and gave up-to-date construction information.
  • Held media events prior to and during construction and used television, print, billboard, and social media to educate and expose the public to the Flex Route.
  • Created a Flex Route educational brochure and worked with local communities to place Flex Route information in their community newsletters.
  • Generated excitement and recognition for the Flex Route and celebrated its opening with a ribbon cutting with local, regional, and state agency representatives. The governor of the state of Michigan and MDOT Director Kirk Steudle were in attendance to celebrate the corridor’s innovation and modernization.


  • Improved system reliability and planning time during the peak hour by 56% southbound in the morning and 27% northbound in the evening.
  • Improved system travel-time during the peak hour by 45% southbound in the morning and 15% northbound in the evening.
  • Improved corridor speeds from 43 mph to 62 mph southbound in the morning and from 48 mph to 54 mph northbound in the evening.
  • Improved corridor incident management.
  • Reduced incident clearance time which will decrease the possibility for secondary crashes.
  • Added seven crash investigation sites and emergency pull offs.
  • Improved interchange operations by improving ramp terminals and adding ramp extensions at fi ve interchanges.
  • Reconstructed three interchanges and three bridges and added non‐motorized accommodations for future connection. Bridge improvements included raising the underclearance to address highload hits.
  • Improved work zone operations by providing for an additional flex lane to manage traffic during maintenance and construction activities.
  • Improved corridor aesthetics through CSS coordination with the local communities.
  • Participated in peer exchanges with the Federal Highway Administration (FHWA) and the states of Ohio, Indiana, Pennsylvania, and Oregon to assist in planning, dvelopment, and implementation of other ATM and operational projects.
  • Completed FHWA’s Tools for Operations Benefi t Cost Analysis (TOPSBC) model.

Operations Area of Practice

    Active Traffic Management (ATM)

Content Type

Case Studies & Lessons Learned

Publishing Organization

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