ETCS would possibly permit shorter waiting times for looped local trains.
Simply because the blocks can be much much shorter.
The local train can potentially start rolling a few seconds after the express charges through.
The limit can potentially be pushed down to the time to work the point machines.
ETCS doesn't necessarily shorten block lengths although it can do that more economically and in a targetted way more easily where that's desirable to minimise impact of such operations.
In continuous 3 or 4 aspect signalling, there is less impact from the signalling than generally appreciated. It is the track configuration itself that is the major constraint.
By way of example, here is my video of a passing manouevre at Dawlish Warren, in the Up direction
First, here's the layout, from Open Train Times:
Here's my video, shot in October 2014
00:00 As the video starts, the squeal of brakes can be heard as a Sprinter comes to a halt in platform 2.
00:05 Sprinter is fully stationary at platform 2.
Ahead we can see (from left to right) signals E123 (up loop), E23 (up main) and E223 (fixed red at London end of down loop). All at red.
Through the wind-blown leaves of the tree on the far right of the frame, signal E25 can also be made out, showing green.
00:51 Signal E23 clears to green.
01:36 Sprinter releases brakes and starts to move slowly towards signal at E123, still at red and approx 340m beyond the platform ramp.
02:30 HST can be heard approaching.
02:35 HST enters, stage left, proceeds to pass the sprinter which is still moving towards E123 at red.
02:49 Signal E23 replaces to red as HST enters route.
03:00 Sprinter easing slowly towards E123.
03:11 HST passes signal E25 which replaces to red.
03:24 Signal E123 clear up to yellow. Sprinter is still moving at this point... it never actually stopped! Sprinter releases brakes, continues rolling, and begins to apply power.
03:49 Sprinter passes through the loop exit points continues towards signal E25 at red.
04:26 Signal E25 clears from red to yellow, as the HST must have cleared the overlap at signal UM202.
04:48 Sprinter passes signal E25 at yellow which replaces to red.
Note loop exit signal E123 clears to yellow only 35s after the HST has passed parallel signal E23. As soon as the fast train clears the loop exit points, they become free to move, so the route out of the loop can be 'over-set' in order that the signal is primed ready to clear to yellow as soon as the fast train clears the overlap of the signal ahead. If the express had been passing through at double the speed this time might be reduced significantly, possibly nearly halved to around 20s under a 4-aspect system with signal spacing adjusted accordingly. Passing times at E25 are separated by 97s, the gap between the trains opening out rapidly as the express continues to race ahead of the slowly accelerating local. By the time the local reached UM202, it may well have been showing a green, especially considering the train was also probably stopping at Starcross.
What can't be seen from this video is that the express is so close behind the local (about 180s) that it almost inevitably saw some adverse aspects on approach. This is the major risk of this type of operation, which is why so much time should be planned into the stopping train's schedule at the loop. Even only a short time lost in station duties at Teignmouth or Dawlish en-route can so easily knock on to a following express if the margin is too tight at the loop entrance. I suspect the local was running late in this case or perhaps the fast was out of path and signallers were attempting to keep it rolling most expeditiously.
