GWML Thames Valley

The Great Western Main Line (GWML) runs from the terminus at London Paddington out to Bristol, Wales, Exeter and Cornwall. Four track sections of the line use the somewhat unusual designations of "Main" and "Relief", rather than the more usual "Fast" and "Slow". Electrified relatively recently, suburban commuter services are between London and Reading are operated by TfL's Elizabeth Line, while all other services are operated by Great Western Railway.

GWML Thames Valley
Description	Great Western Main Line between West Drayton and Twyford, including the Thames Valley branches.
Country	United Kingdom
Time period	2026
Train Operating Company	Great Western Railway, Elizabeth Line
Simulation difficulty
Author	Oxalin
Repository	GWML Thames Valley
Website	GWML Thames Valley
Rolling Stock	Class 165 Class 166 Class 345 Class 387 Class 800 Class 802
Route map Henley-on-Thames Shiplake Shiplake Viaduct Wargrave Great Western Main Line Twyford West Twyford Ruscombe Jn Marlow Bourne End Cookham Maidenhead Stabling Sidings Furze Platt Maidenhead Reversing Siding Maidenhead Maidenhead East Jn Maidenhead Viaduct Taplow Burnham Windsor & Eton Central Slough West Junction Slough West Loop Slough Tamper Sidings Slough Dolphin Jn Langley Langley Loop Iver Great Western Main Line

This simulation covers the section of GWML between West Drayton and Twyford, and includes the three "Thames Valley" branches to Windsor & Eton Central, Marlow, and Henley-on-Thames.

Timetable

A timetable representing Wednesday 4th February 2025 has been included, starting at 03:45 and running a full 24 hours. The line sees plenty of freight throughout the day, especially overnight, so there's always something happening!

In the early morning and late evening, the line operates as a two-track railway using just the relief lines (the upper two tracks in the simulation). During the day, services are mostly seperated with Elizabeth Line and Freight using the Reliefs, while GWR services use the Mains. However, some GWR semi-fast services cross between the Main and Relief lines - generally at Dolphin Jn near Slough, but during the peaks they can cross at other junctions along the route.

The standard off peak service is as below. On the day this timetable represents, engineering works meant trains to Swansea and beyond terminated at Port Talbot Parkway, and trains to Oxford and beyond terminated at Didcot Parkway. This likely reduced the service frequency slightly, although it still gets very frantic during peak hours.

GWML Thames Valley Services
Train Operating Company	Origin	Destination	Frequency (tph)
Great Western Railway	London Paddington	Didcot Parkway	2
		Cardiff Central	1
		Swansea	1
		Oxford	1
		Great Malvern	1
		Cheltenham Spa	1
		Bristol Temple Meads	1.5
		Weston-super-Mare	0.5
		Newbury	1
		Exeter St Davids	0.5
		Plymouth	0.5
		Penzance	0.5
	Slough	Windsor & Eton Central	3
	Maidenhead	Marlow	1
	Twyford	Henley-on-Thames	2
Elizabeth Line	Abbey Wood	Maidenhead	2
		Reading	2

Additional services run in peak hours, with some Elizabeth Line services extending to Reading and extra GWR services crossing to the Relief Lines.

Most notably during peak hours, a second train joins the Marlow branch. Instead of running the full length, one train shuttles between Maidenhead and Bourne End, with the other shuttling between Bourne End and Marlow.

Operational Tips

• Where important, platform allocations are provided in service descriptions - it's best to stick to these or trains might not be able to get to where they need to go.
• Passing times at junctions are only provided when trains are meant to cross between Mains and Reliefs there. Due to design limitations, Slough West junction couldn't be named - instead passing times are provided for "Slough Signal 536 / 6284" in these cases.
• Pay particular attention to 9N06 at about 23:40. This service crosses over at Dolphin Jn to the Mains, then back to the reliefs at Slough West Jn. This is to allow a GWR service to overtake at Slough.
• Almost all trains can use either line at exit points in case of disruption. However, there are some exceptions to this. The following freight trains leave towards London on the "Iver Loop", the top track on the screen. Most of these can also exit on the Up Relief as normal, but some are set to only accept the loop line.
  • 4M55
  • 4M60
  • 6A40
  • 4L33
  • 6M91
  • 6A61
  • 6A90
  • 4M79
• Pay attention to passing times - sometimes trains may have to be held at red signals to keep them in the correct order.