Riddles put his case for continuing to build steam locomotives in his presidential address to the Institution of Locomotive Engineers in November 1950. He compared capital costs to show that steam was cheaper than the alternatives, though he didn't mention productivity differences, except to say fuel costs did not rank very high relative to total costs. For example, a Class 5 cost £16,000, compared to £78,100 for a 1,600 h. p. diesel, £138,700 for a gas turbine, or £37,400 for electric. He calculated the costs per drawbar horse power as £13 6s (steam), £65 (diesel), £69 7s (turbine) and £17 13s (electric). Riddles retired in 1953.