The train journey from Cardiff Central to Bristol Temple Meads is among on one of the slowest in the UK - taking 55 minutes at 30mph.
New research has found has found that trains connecting some of the UK's major towns and cities are up to four times slower outside of the South East.
Press Association analysis of the quickest possible trains on 19 routes found that services from London travel at average speeds of 65-93mph, compared with just 20-60mph elsewhere.
Passengers travelling from London to other destinations often have the choice of non-stop trains, which means the journey times are shorter.
Many of the slowest routes featured in the analysis are only served by trains with multiple stops.
Think tank IPPR North senior research fellow Luke Raikes said slow journey times were "down to decades of under-investment as the Government has just responded to congestion problems in London".
Last month, Transport Secretary Chris Grayling supported a new £30 billion Crossrail 2 scheme in London and the South East, days after a series of rail electrification projects in Wales, the Midlands and the North were axed or downgraded. This included the UK Government scrapping the electrification of the railway line between Cardiff and Swansea.