The basic claim is accurate. The last four price rise added (multiplied in the case of % rises) together come to 20.5% although you could quibble that the 2011 rise was almost certainly in the system and locked in before the Coalition had any chance to influence it. Which is a clue to the greater truth. These figures from Railfuture tell all.
This year’s rail fare rise was the lowest real terms price increase for 11 years if you think RPI is the measure of choice for inflation (as people do when they want inflation to be high). It was also the 2nd lowest nominal rise for 11 years.
Both Labour and the Coalition stuck to rail fare price increases of RPI+1 for ten years from 2004 in the belief that the burden of paying for rail transport should be shifted from the state to the passenger. This is the first year that the rise has been restricted to RPI rather than RPI+1.
So the Cost of Cameron is lower this year than the Cost of Blair and the cost of Brown. If the Cost of Miliband is going to be lower perhaps he will explain how it will be paid for?