Interesting cost comparisons from the latest "In the Loop" BNV email...
According to the ABC, in Queensland the costs line up like this:
1km of rail costs the equivalent of 29 kms of bikeway
1km of motorway/road costs the equivalent of 110 kms of bikeway
1km of busway costs the equivalent of 138 kms of bikeway
1km of road tunnel costs the equivalent of 324 kms of bikeway
1km of underground rail costs the equivalent of 533 kms of bikeway.
Now if you assume a freeway is carrying three lanes of traffic and a bikeway just one, and you assume that car occupancy rates are, as reported, 1.2 persons per vehicle (pm peak, am peak is cited at 1.09), and you assume that motorists and cyclists are maintaining adequate, safe separation then...
At peak hour freeway speeds of, generously, 40 kph (11 m/s) and a 2 second, minimalist, following distance that's 22m between 6m long vehicles = a total length of 28m per vehicle. Divide that by 1.2 people per vehicle and divide by three lanes and you get about 8m per person. At 60 kph the following distance increases by 50% which, ignoring the car's own length, increases the metres per person by a similar amount to 12.
At peak hour cycle commuting speeds of 20 kph (average!!, not wacky races winner) it's fair to say a 2m long bike can safely follow at considerably less than 6m behind the bike in front so 8m per person is a maximum requirement.
So, even after allowing for the different widths and making the most pro-motoring assumptions possible, the costs of road infrastructure vs bike infrastructure still stands at 110:1 per person moved.
The figures for persons moved per hour over a given distance, given the higher speeds, may be somewhat less. Too tired to work it out right now.