Transport planning chief Eddie Luck warned of long queues if a bridge remained two-way when new shops were built nearby.
He said additional traffic from the planned £30m Orchard Centre redevelopment in Didcot would overload a new junction with Station Road during peak hours.
Mr Luck told a meeting of residents of the new Ladygrove estates north of the railway line that keeping Cow Lane Bridge two-way would also create serious safety problems for cyclists.
Mr Luck, the county council's chief transport planner, defended a proposal to make the bridge underpass one-way southbound.
Mr Luck said: "It would allow direct access to the station for commuters and other rail users, and the town centre.
"Return routes to Ladygrove are available via Marsh Bridge and Manor Bridge."
But the proposals were greeted with dismay by some residents who complained about the wide detour east and west of the town which would be necessary for people going to Ladygrove.
Public consultation on the plans will start on Friday, March 23, before the traffic regulations order for the section of the Didcot-Milton Heights link road between Cow Lane and Jubilee Way is considered by the county council on May 24.
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