District and Hammersmith & City line part closures

I'm very preservationist in this regard, too, and I think it's a shame to lose emergency crossovers and, arguably, quite short sighted.

However, another point is that trailing crossovers, such as at Hornchurch, make less sense with high frequency train services. This is because, if you want to reverse east to west at Hornchurch (to take the example), you have to change ends in the platform (which takes time, especially if platforms are busy), wait for a gap on the westbound and head over the crossover. All the while this is being carried out, the eastbound is blocked by the reversing train and other trains are likely to be held up. Even with TBTC, depending on the location of the crossover, it may - additionally - not be possible to bring a train into the westbound platform, which can hold up the westbound as well. On top of this, you now have the issue of a trainload of passengers being dumped on the eastbound platform, and passenger confusion, with people wanting to go east ending up heading off in the wrong direction. Now, obviously, the clogged up platform is gonna further delay following eastbound trains, as it will increase dwell times, which will likely ripple back if you're running very high frequencies.

In fairness, all of this is less true at Hornchurch, but if you think of places like South Ken and Bromley-by-Bow, the scheduled services are very frequent and it's often better to let a late running train carry on (say to Barking, in the case of Bromley-by-Bow), than to try to recover time using an emergency crossover, because you just end up delaying following trains instead/as well.

So with resignalling set to increase frequencies, it's not unreasonable to predict that crossovers like these will become even less useful, primarily being relegated to planned engineering works. But you simply can't run a respectable number of trains if all trains are terminating somewhere like Hornchurch, because you've just got the one platform. Which is why scissors crossovers are being brought in in places like KCSP and Westminster, because then you've got two platforms to play with.