FALMOUTH — Trucks weighing more than 22 tons will be barred from Railroad Crossing Bridge starting Tuesday.

The state Department of Transportation is posting the weight limit due to the deteriorating condition of the steel structure, which carries traffic from Routes 26 and 100 over the Presumpscot River. MDOT engineers also wanted to keep the bridge open during construction of the replacement bridge.

The weight limit is expected to allow most vehicles, including pickup trucks, school buses and emergency vehicles, to continue using the bridge.

Trucks weighing more than 22 tons will be rerouted to the Washington Avenue Extension, Blackstrap, Brooks and Leighton roads – a detour that will add about 0.8 mile to their route. Heavy trucks can also use the Maine Turnpike. MDOT estimates about 350 trucks will use the detour each day.

Railroad Crossing Bridge was built in 1932. The replacement bridge project downstream is expected to be completed within 11 months, after which the old bridge will be dismantled. The replacement cost is $10.5 million.