Your suggestion to abolish road fund tax, replacing it with an increased fuel duty is also eminently sensible, though not the headline grabber of the punitive rates of road fund for high emission vehicles proposed by our so often misguided government.
I cannot, however, agree with your justification for road pricing on the basis that car use is cheap compared to rail. Yes your journey by rail would have cost £70 but your car fuel cost of £40 is not the figure that must be compared with the rail fare.
Even the HM Revenue and Customs recognise that the car costs at least 40p per mile and if you consult the figures given by motoring organisations such as the AA you can generally treble that figure even for a modest vehicle.
You don't state the distance travelled but at 110 miles each way a conservative estimate of your car cost is £88, more than the train.
Taking climate change as a definite phenomenon created by man, we do need to ensure that travel uses the minimum carbon possible and road charging may help this aim, however, cars are not cheaper than the train for a lone individual.
AL SYKES (M), firstname.lastname@example.org