Work started Tuesday on the southbound bridges. Work on the northbound bridges is expected to begin next week.
Two of three southbound lanes are closed to allow workers to make repairs to a pier under the bridge. Other work includes patching the bridge deck and substructure repairs.
MDOT scheduled the work to begin in June, but the contractor was not able to start the project until this week.
Some drivers attempted to avoid the highway lane closures by using M-120 and Whitehall Road as an alternate route and crossing the Muskegon River at the Causeway Bridge. Police in Muskegon and Muskegon Township say traffic on that route has been significant since Tuesday. There have been backups and some minor crashes relating to the increase of traffic from drivers avoiding U.S. 31.
There's plenty of notice to drivers of the approaching lane closures on southbound U.S. 31. However, some drivers might not expect a two-lane merge.
"Motorists just need to be courteous and let folks in and try to keep the flow going as best that they can," MDOT spokesman John Richard said.
The work is scheduled to be completed in November. But the late start might prevent workers from finishing this year, Richard said.
"We hope to get both northbound and southbound done this year, but if we don't because of weather reasons and contractor schedules, then we'll get as much as we can done this year, and then next year probably May or June we'll finish it up," he said.