Directly connecting England and Wales, running under the longest river in the United Kingdom, the South Wales Main Line is one of the most important cross-border routes in the UK The locos: The British Rail Class 175 Coradia 1000 is a type of diesel multiple-unit passenger train operated by Transport for Wales Rail in the United Kingdom. The fleet of 27 sets was built between 1999 and 2001 The British Rail Class 153 Super Sprinters are single-coach railcars converted from two-coach Class 155 diesel multiple units in the early 1990s. The class was intended for service on rural branch lines These trains will run along the Cardiff Bay branch Pictures: Class 153 in Cardiff Bay Class 175 in Swansea If you own Gwe you can layer the class 43 over to do services on this route
To be honest there would be little purpose in making the 153 for a two-station shuttle operation. I included part of this line (Bridgend - Cardiff) with some surrounding lines in a similar suggestion: https://forums.dovetailgames.com/threads/south-wales-network-class-800-143-150.40378/
