Tolls are no longer being collected on the Erskine Bridge over the Clyde.
Transport Minister Tavish Scott announced last month that removing the tolls would ease congestion on river crossings in nearby Glasgow.
The move sparked calls for an end to tolls on the Tay Bridge and the Forth Road Bridge.
The National Alliance Against Tolls Scotland said ministers were afraid of
"trumpeting" the economic benefits of removing tolls.