Thread by @NetworkRailSE

A few people have asked why the "new" platform 7 at Gatwick isn't level with the doors on the train in the pic and why we couldn't just build it higher. It's a sensible question and to save everyone getting a slightly different answer, here's why... /1

https://twitter.com/NetworkRailSE/status/1321030920393117696

Very few mixed-use (freight and passenger) railways anywhere in the world have true level access to trains. As the owner of a legacy system dating back to the 1830s we're often in the position of having to make the most of a bad hand and our platforms heights are no different. /2

Over time we've alighted on a standard platform height of 915mm across the UK, with some room for variation. That standard is what all train providers work towards so all their stock (freight and passenger) will run past platforms without scraping them or worse. /3

Stationary or low-speed trains don't wiggle about much so this picture gives the impression we could add a few inches to the platform to match the doorsteps and all will be well, especially as it's straight. /4

...but a moving train - and trains run through Gatwick at over 50mph - move around quite a lot and were the platform at the same height as the train doors, we'd need to move the track away from it to stop trains whacking it at speed. You'd still need a ramp to get on and off. /5

That's not even considering freight trains, of which there are quite a few on this line, which are of different sizes and heights, albeit all within a prescribed "envelope". Again, a higher platform would get struck by their wagons, and we would be in trouble. /6

While this platform is straight, many are not, and on those platforms a level height would require the track to be even further away, as the corners of train carriages swing out on curves. Added together those are the "kinetic envelope"... /7

... which means we have to design the railway around a bigger size (or envelope) than a stationary train in a picture would suggest. The reason for sticking to a standardised height is that we know that trains will run past platforms curved or otherwise, with no problems /8

What can be done though? Well, multiple train types use Gatwick's platforms so a standard height is sensible, but on platforms at stations only served by @TLRailUK class 700 trains, we've built "humps" that match their accessible coaches. /9

That allows for level boarding in those particular coaches, but at stations with multiple train types and freight, we need still need to use ramps. There is another alternative, which is to lower the doors on trains and build ramps into the trains themselves. /10

That is already happening on some train fleets, and new railways - which only have a single type of train ever using their platforms - can have higher standard platform heights. That's the case on some Tube lines, for instance. /11

So to conclude, we realise it was a more complicated answer than many of you hoped for, and we also know how important it is for passengers with wheelchairs/buggies and luggage to have simple, easy journeys. /12

...which is why Gatwick is being rebuilt with more lifts and wider platforms, and why our colleagues at stations are so important to making sure all our customers are safe and happy on their journeys. We hope that explains it. /Ends