Traffic Signal Design Considerations

The Michigan Department of Transportation (MDOT) is in the process of updating the MDOT traffic signal standard plans, along with structural designs and detailing in accordance with the requirements of the current version of AASHTO LRFD Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals First Edition with Interim Updates (AASHTO LRFD LTS-1).  Refer to the Final Rule to amend Title 23 Code of Federal Regulations Part 625 in the Federal Register on January 3, 2022 which prompted this update.  It is anticipated that the updated MDOT signal design standards will be complete by the Fall of 2022. Among the revisions to the MDOT standards will be the addition of wind loading considerations which are not currently included in the MDOT Design Guide “Signal Design Calculator Spreadsheet” tool often used by designers.  

For projects which include additional loading to existing traffic signals/arms/poles (EX: backplates, beacons, etc.), structural analysis is required to ensure all structural members are appropriately proportioned for the various controlling load combinations. Designers are responsible for reviewing the structural capacity of the existing poles/mast arms and foundations to determine if the structures (including foundations) can safely support the proposed modifications, or if retrofitting will be required.  All structural calculations must be performed, stamped, and sealed by a licensed PE in Michigan.  These calculations must be kept in the Local Agency’s project file and available upon request.

Use of the updated standards is required for all GI (Grade Inspection) submittals on or after February 2, 2023.