Launched last summer, volunteer participants are given the choice of paying a fee to drive into the centre of the city or taking a high-speed bus from a park and ride at a reduced cost. Tolls are £5 between 7.30am and 8.30am and £2 during the rest of the day. However, for a week in February the peak time toll was doubled to £10. During this time the percentage of people using the park and ride bus service dropped from 29%, in the first half of the month, to 24%.
Jonathan Smith, of the Transport Research Laboratory, which designed the scheme and is researching its impact, said: 'We found quite a few people shifting route and going out of their way to avoid the tolls. We had thought people might switch the time of their journeys, but that did not seem to happen.'