Here are a couple of quotes / sources. You may want to look closer than I have at more from these researchers:
Between 1981 and 1995 the spending on federal highways in the US grew from $9 to $19 billion whilst transit stayed at $4 billion.
-Peter Newman and Jeff Kenworthy
In the current tax and fee payments to the government by motor-vehicle users fall short of government expenditures related to motor vehicle use by approximately 20 to 70 cents per gallon of all motor fuel.
-Aaron Naparstek, UC Davis Institute for Transportation Studies
A comparison of the relative efficiencies and costs of road and rail:
A standard twin track railway has a typical capacity 13% greater than a 6 lane highway (3 lanes each way), while requiring only 40% of the land. -Highway Capacity Manual
A basic formula of traffic engineering states that one lane of limited access highway can accommodate 2300 cars per hous, while one lane of light rail can accommodate 40,000 passengers per hour. -J.M. Kunstler, The Geography of Nowhere
Here's some info on the cost of a road:-
A mile of new motorway costs on average £30m, according to the Highways Agency. As a rule of thumb, an elevated road costs 10 times more than one on the flat, says French.
The most expensive road per mile is the Limehouse Link. The 1.1 mile (1.8 km) tunnel in London’s Docklands opened in 1993 at a cost £293m. Adjusted for one measure of inflation that would be £445m or £230,000 per yard (£250,000 per metre). It was designed and built in seven years and at the time was the second biggest engineering project in Europe after the Channel Tunnel.
The UK’s last, great, expensive, short roads, Tom de Castella
Here's a short history of the road lobby:
‘National Highway Users Conference’, pioneered by General Motors’ Alfred Sloan which, in 1932, brought together automobile, oil and other highway interests to lobby for road funds and an end to mass transit funding. The result was the U.S. Highway Trust Fund through which the U.S. government spent $1,845 million on highways between 1952 and 1970, while rail systems received only $232 million.