snorri said:
Then you must arm yourself with some facts, here is a starter for you.
http://www.parliament.the-stationery-office.com/pa/cm200708/cmselect/cmenvaud/907/907.pdf
I would refer you to Page 7 para 4 where you see the tax was introduced in 1909 in order to fund maintenance and construction of roads. This hypothecation ceased in 1936 following passing of a Finance Act. The term Road Fund Licence or Road Tax is still used incorrectly to describe Vehicle Excise Duty, a duty which bears no relation to the costs to the nation of provision of our transport network.
Also
http://www.parliament.the-stationery-office.co.uk/pa/cm200405/cmselect/cmtran/218/21805.htm
See para 7,
where you will note only some of the costs are borne by the road user, others are borne by society at large.
Trouble is, it's rather difficult to quote these websites and paragraphs to car drivers whilst negotiating city traffic.
Not really true, though, since neither VED or duty on petrol are spent directly on roads. All taxes and duties get mixed together and spent on whatever the Govt. wants to spend it on. Those who pay the most taxes overall pay the most for roads, and also most for the NHS, public sector pensions, the emergency services, schools, prisons, wars, legal aid, welfare, Britains contribution to the EU and so on. As a general rule that means that the highest earners pay the most and the low and unwaged pay the least.
Now, cycling is far more popular with the relatively well-paid middle-classes than it is with those earning below-average wages, or living on benefits. Even though cycling is cheap, poor people tend not to do it, though they might find the money to run a car. The average cyclist earns more than the average wage, and therefore contributes more to the economy, including the roads, than the average non-cyclist.
This does not give them more right to use the public roads, which are free at the point of use to everyone irrespective of how much tax they pay, just like all other public services. But anyone, whether or not they own a bike, has to pay duty on any motor-vehicle that they use on the public roads.