They take as the crow flies distances, divided by the journey time by rail, which would be over a longer route, maybe significantly so if not direct etc.
Seems to be a manufactured story appearing in many papers, eg this one from
Leicester
Rail journeys from Leicester are among slowest in country
Rail journeys from Leicester to all other major British cities average just 39 mph, exclusive new analysis reveals.
Research into hundreds of train routes has revealed that, of the 20 biggest cities, only passengers in Bradford, Nottingham and Coventry face slower rail journeys to any of the other cities.
It found that rail journeys from Leicester to the 20 other biggest British cities average 39 mph, including waiting times, which is below the national inter-city average of 42 mph.
Included in the above is: 16-mile journey from Southampton to Portsmouth takes travellers an hour, on average
An hour is the longest journey by rail; a more typical one would be 41 minutes. The hour-long journey has over a dozen stops.