Such a road pricing scheme when drivers have to pay per mile have many benefits in terms of reducing negative externalities, however there are some arguements against this policy.

There are many external costs arising from the use of private cars such air pollutions, traffic jams and time wasted in traffic jams, decrease in efficiency and loss of time; in order to cope with all these problems government as one of the solutions might introduce charging scheme and this will be an effective way since there 'pay as you go' principle will work and every driver will pay as much as he has driven and so this would be more equitable. However, on the other hand, the question of equity will still arise, because people from different backgrounds will have to pay the same amount and thereby there regressive taxation system will work since the poor will spend a bigger proportion of their income on it.
Another advantage of this charging scheme is that it might be really helpful in reducing congestions on major roads and thereby reduce negative externalities. But the problem for the government is the amount of tax that has to be charged per mile.
As you can see from the graph below there wasn’t any market failure before the line started to diverge.



This occurs because volume of cars reached the point when negative externalities appear. Market equilibrium will be at point B, while social equilibrium where external effect is internalized is at point C. If government introduces prices which covers all the costs from congestions, volume of traffic will fall from Q to Q1 and price will increase from P to P1; the net social gain from saved congestion costs is shown by triangle ABC. However, since it is almost impossible to calculate exact price for all the costs, it would be very difficult to achieve such situation.
Another problem with this charging scheme is that instead congestions on smaller roads might appear where drivers have to pay fewer taxes and as these small roads usually increase journey, more time will be lost and more delays might occur.
Moreover, there is an ethical issue about the scheme of having electronic tags in each car since every car will be under control by government which can spy all your journeys. (Big Brother problem)

something about tfl =)))

Transport for London is a huge programme carried out in London in order to improve it’s transport infrastructure. This investment project is aimed in five years make some improvements in different types of transport, make green types of transport more attractive and move to sustainable transport system that is a system that makes contribution to the environmental, economic and social sustainability.
Fall in 6,4 % in August due to recession brought many problems into the whole transport system which was planned ahead. This decline in demand for underground might be caused by switching to it’s cheaper substitutes or by fall in income.
Decline in revenue due to decrease in demand for underground complicated questions of TFL funding as they wouldn’t receive the same amount of money and so will have to find other ways of finding money for their project. Managers of TFL project will have to work hard in order to raise demand for underground even if there is a recession. Peter Hendy, London's transport commissioner, said "Revenue is not where we expect it to be in this year's budget. A decline in revenues now will also have a budgetary effect in the years to come".
As there is a fall in Tfl finances, managers of it cannot be sure whether it will be possible to end the programme in five years and make all the changes that were planned to do. In order to have an adequate Tfl has to either increase number of passengers or raise prices for tickets. However, Tfl have very pessimistic expectations about the former, while the pressure on fares will be and prices for tickets might increase by almost 6% next year already if number of passengers remain the same.
Also Tfl will have to continue to seek reductions in costs of improving infrastructure and remain efficient and useful.
Another consequence of this decline in revenue might be that some constructions which are already started will have to be delayed in continuing and so possibly create traffic jams or increase time spend on the way to work for people and thereby they would be more tired and annoyed, and thereby lose concentration.
Because of decline in demand for underground Tfl is not sure whether demand will rise again and if it rises, how much and so it is difficult to plan how many trains will be needed and how other types of transport have to be improved; whether buses will be more demanded rather than underground or not.