I originally wrote this blog in response to some anti Hs2 nonsense back in November 2015. I’ve revised it now as it’s a useful look at the pros and cons of double-deck trains – especially in the UK as DD trains are one of the things opponents of Hs2 often say are a viable alternative.
How can double-deck trains fit in the UK?
The simple answer is – they can’t as things stand. The UK loading gauge on most routes simply precludes their use. But this is not just the height of trains we’re talking about – it’s the length of the vehicles too. Let’s delve into a bit of history. When our Victorian network was built the railways ran short (30ft long) 4-wheel coaches. In fact, these were still being built right up to the end of the Victorian era. What this meant was the railways could get away with some tightly curved platforms and tracks as the coaches could fit around them.
The picture above shows Clapham Junction now with a train of 19.83m long class 455 vehicles in platforms with a pretty fierce reverse curve. Fancy trying to fit longer vehicles in here without the horrendous rebuilding costs & disruption to the UK’s busiest station that would entail?
Gradually (to improve comfort & with the invention of the bogie) coaches got longer & some doubled in size to reach 60-62 foot long. The issue with this is (and always was) the overhang of the coaches on curves which governs how tight platforms & other infrastructure can be. For many years British Rail standardised on coaches that were 57 ft 0 in (17.37 m) or 63 ft 6 in (19.35 m). Eventually the Intercity fleet standardised on 23m long vehicles whilst commuter and local services used 20m long vehicles as the maximum that could fit many tight platforms.
Why does this matter to double deck trains? Simple – because of the amount of room taken up by stairwells and all the ancillary equipment that used to be slung beneath the underframe between the bogies (where the lower deck is on DD coaches) but now has to be fitted inside the bodyshell. Here’s a few examples.
There’s no benefit on capacity of a double-deck 20m vehicle as the stairwells at either end take up so much room it cancels out the seats provided on the upper deck. A 23m vehicle will give you around 12-13% extra capacity. It’s only when you get into longer vehicle lengths that DD coaches make sense. But here’s the rub – those longer coaches won’t fit on much of the network. Not only that, but they would even be restricted on some lines they could because of the curvature on certain station platforms or tight curves where they’d foul adjacent lines. For example. SouthWest trains use 23m long Class 444s – but these were banned from platforms 1-4 at Waterloo (thus reducing the flexibility of the railway). Those platforms were recently rebuilt and lengthened at great expense and disruption.
Oh, and don’t even ask how much headroom you might have on the top deck. Even in Europe this can be quite tight. With the UK’s restricted loading gauge you’d be lucky to be able to stand upright if you were above 5’6″- hardly good when the average height is 5’9″ & will only increase over the next few decades!
So, what seems a simple idea proves to be increasingly complex when you look at the details – something the anti hs2 mob never do anyway. Put simply, the capacity to be gained from double-deck trains doesn’t make up for either the cost of adapting the network to make them fit or the reduction in operational flexibility (and thus track capacity). What you gain on the swings you lose on the roundabouts.
You could add 12-13% capacity to coaches at great expense, but reduce the overall capacity of the railway and find your gain is even less. But how much time does that 13% buy you? At the current rate of growth it’s less than a couple of years on some routes. At best it might be a decade on others. But at what cost? In 2005 Stagecoach carried out a study into running DD trains & found just the short bit between Waterloo and Clapham Junction would have cost almost £1 billion to convert for full-scale double deck trains (The Times, June 2005).
Then what?
Oh, and double-deck trains don’t add an ounce of track capacity – exactly the opposite in fact. You might be able to fit a few more people on the 08:10 from Euston to Birmingham, but the dwell time (the amount of time it takes to load/unload passengers) at intermediate stations is much longer for DD trains than normal ones, so the train that’s only a few minutes behind is rapidly catching up with you, leading to delays. If you want a reliable timetable you have to cut trains out of it, negating the whole point of the ‘extra’ capacity.
This is a serious ‘alternative’ to Hs2? Of course not. Hs2 is designed to take intercity trains off the classic network. DD trains don’t add any capacity to our lines, they simply allow a few more folks to get on existing services. besides, would you want to travel long-distance in one of these cramped vehicles?
It’s time the anti Hs2 mob stopped grasping at silly straws.
Paul Bigland 
Of course there was a line in Britain where double deck trains once ran in the form of the Bulleid 4DD. And this time last year Network Rail threw open the concept of double decking parts of the South West mainline.
Somehow though, I just can’t see it happening.
I think the anti hs2 groups seem to be living in a completely different world to the rest of us – suggesting that because double decker trains have been used before on UK rails that they would work fine on existing lines – yet the ones that did run had little head room & long dwell times.
Indeed. What they ignore is how unsuccessful those Bullied commuter EMUs were and how limited their use was (London Bridge – Dartford). Really, they’re just grasping at every straw they can clutch.