what exactly is the price per litre?
I wrote about prices in the UK around a month ago when we reached a new record average price of 96.13p:
UK Petrol Prices.

The point about travel times is interesting and I can certainly believe it is a universal.  I wonder however what a similar analysis on travel costs would show though.  What proportion of income has typically been spent on travel over the ages?  I suspect that has been falling, certainly over the last couple of decades in the UK the cost of motoring has been falling.