MDOT Implements Bridge Under-Clearance Buffer

Effective Monday, May 4, 2020, the Michigan Department of Transportation (MDOT) will implement a two-inch buffer for structure under-clearance as part of their review for all Transportation Permits. This under-clearance buffer was approved by MDOT’s policy body on technical matters, the Engineering Operations Committee, at their January 21, 2020 meeting on the basis that it is in line with permitting best practice followed by many other states to reduce damage to the highway infrastructure.

Under the current permitting process, the MDOT permit system reviews a route submitted by a permit applicant, and the permit is approved if the vehicle height is less than or equal to the measured under-clearance.

When the buffer is implemented on May 4th, the two-inch buffer will be taken from the point of minimum vertical clearance (not the posted height of the bridge) when the permit system analyzes the allowable height of an over height permit along a route. Permit applications that exceed the two-inch buffer will not be issued.

MDOT states that the new practice provides a buffer to account for several potential items that would cause the allowed clearance to deviate from the measured clearance, and thereby reduces the risk of over height impacts.

Click here to view MDOT’s letter to MITA on this matter.

If you have any questions, please contact Glenn Bukoski, VP of Engineering Services, at, or Rachelle VanDeventer, VP of Industry Relations, at