Trains are being upgraded to give disabled passengers access to the Bedford to Brighton, Wimbledon and Sutton rail route.
Two of the refurbished Thameslink trains are already in service with 78 more to follow.
They will feature wheelchair friendly toilets, wheelchair spaces, new sounders for the opening and closing of doors and new on-board electronic information screens.
Thameslink also recently announced that it is about to trial the first of 29 brand new Class 387 trains on the Brighton to Bedford route.
These feature in-built facilities for the disabled as standard.
Customer service director Keith Jipps said: “Since we took over Thameslink services in September, we have announced the introduction of a brand new fleet of modern trains. Now we can confirm the upgrade of the older trains on the route.
“This is great news for Thameslink passengers with restricted mobility. The new wheelchair accessible toilets are fresh and modern and the newly widened priority areas will make journeys easier and more comfortable.
“With new footbridges with lifts at stations like Elstree and Borehamwood and Harpenden, we hope to deliver a real improvement for passengers.”