Hurrah, yesterday it finally happened, after umpteen years of upgrades. From two carriages to three, this is indeed a 50% increase in capacity, and East London's DLR travellers should all be feeling jolly chuffed. Except it's not quite as good as the headline suggests.
Yes, this is only an improvement on one of the DLR's routes. The rest are all stuck with two carriages "until demand requires" (i.e. for the foreseeable future). This may be a 50% increase on part of the network, but it's rather less than 50% overall.
Yes, there's only one three-carriage train at the moment. There'll be more soon, but not yet. Lucky you if you manage to find it, that's a 50% increase for your journey. And bad luck if you don't. The DLR owns enough carriages to run about 50 trains, so if one of these gains one extra carriage then I calculate this to be a 2% increase. There'll be a far greater boost in capacity eventually, obviously, as more and more three-carriage trains are introduced, but for now the actual increase is rather tiddly. More like...
Lucky me, I managed to find the big one. It pulled in beside me at Poplar station last night, (which surprised me, not being on the Bank to Lewisham route) and proudly filled the complete length of the extended platform. Alas the guard then promptly kicked everybody off so that the train could roll back into the depot, so I didn't get to go for a ride.
But you might be more fortunate. You might stumble upon this magic extra 2% while it's properly operational, and smile at actually finding a seat for a change. But hurry if you're intending to ride it to Bank, because Bank station seizes up for escalator work next week, remember, and YOU MUST AVOID BANK STATION AT ALL COSTS(OR ELSE). All that extra capacity, and nowhere to go.