The typical inter-city journey in Britain is about 100 miles. Now look at this table of speeds and journey times; remember that to achieve an average speed of 100 mph will involve a period of running at 120 mph or more. 30 mph, 3 h 20 m 40 mph, 2 h 30 m 50 mph, 2 h 60 mph, 1 h 40 m 70 mph, 1 h 26 m 80 mph, 1 h 15 m 90 mph, 1 h 7 m 100 mph 1 h The time savings for each successive 10 mph speed increment are 50, 30, 20, 14, 11, 8 and 6 minutes respectively. It is a situation of diminishing returns. It gets worse than that, because there are break points. 50 mph is the maximum operating speed for light rail. After that, the regulations for heavy rail come in, which affects safety standards, signalling systems, vehicle design and track design, with engineering costs to match. At 100 mph, the EU’s Technical Standards for Interoperability apply, which are even more stringent; at over 125 mph, there is another step change, in design requir...