The group Trafficmaster monitored the Forth Road Bridge near Edinburgh for five days before and five days after northbound tolls were abolished Feb. 11, The Scotsman reported. The group found that the morning rush hour -- which averaged 61 minutes while tolls were in place -- lengthened to 91 minutes once the bridge was free.

Three of the five days after abolition were school holidays, when traffic in Scotland tends to be light.

Experts warned the government about the effect while the decision was being made. Finance Secretary John Swinney advocated abolition, arguing that it would stimulate the economy.

The results suggest that drivers respond to economic incentives.