But the predicted increase in traffic on Victoria Road has failed to materialise, the latest data from the Roads and Traffic Authority shows. The number of cars crossing Ryde and Gladesville bridges fell during the peak.

In the first two weeks of variable tolling, the authority registered a big rise in early morning trips. Compared with last year, there has been an increase of more than 13 per cent in the number of motorists using the bridge and tunnel between 5.30am and 6.30am when the toll is still at its overnight rate of $2.50. That is 8415 extra car trips in the fortnight. But many of those will have been made by the same driver.

On average, 561 cars per day took advantage of the cheaper toll.

Ken Dobinson, a former director at the Roads and Traffic Authority, said the real test would come this month, traditionally the busiest of the year on Sydney's roads.

"The data does show that motorists using the bridge are conscious of the increase in toll in the peak and seek to avoid it," he said. Overall, peak-hour traffic on the bridge and tunnel dropped 14.5 per cent.

But David Hensher, director of Sydney University's Institute of Transport and Logistics Studies, said the number of people who had avoided travelling in the peak was far smaller because of a general decline in traffic. "There appears to be a global effect of about a 2.8 per cent drop in [all harbour] crossings," he said. "My guess is that the price change may account for about a 2 per cent drop.

"We have to recognise the state of the economy which contributes some of this."