Caistor and Brigg are set to see heavy traffic in the area increased this spring due to major roadworks to be carried out on the A18 between Melton Ross and Humberside Airport.
The railway bridge on the A18, a mile east of Melton Ross, will need to be improved and strengthened.
That part of the highway is the responsibility of North Lincolnshire Highways.
Traffic lights and a one way crossing is already in place.
Beneath the bridge is the main rail route east from Scunthorpe to Grimsby.
A survey of the bridge found concerns at the impact damage if a heavy goods vehicle hit the bridge wall.
Traffic diversion when a full closure of the road takes place could last up to three months.
The direction for heavy traffic will be from Brigg towards Caistor coming out near Great Limber.
There will be some additional congestion in both the Caistor and Brigg area due to the diversions.
The road closure at the bridge and consequent diversions are expected to take effect from the beginning of April and last until the end of June.