But not on the level, it can be done by the flyover.
That's a messy move because it means sending it out of P3 or 4, over the flyover and then reversing on the up slow back into P1.
I assume the up slow is bi-directional to allow that move ?
== Doublepost prevention - post automatically merged: ==
As a user, I already regularly see the snow ball impacts of even a 2 minute delay at Welwyn Garden City (on any service) as these rapidly snowball.
I do remember a period where the Welwyn Garden City / Hertford services were every 20 minutes, providing a service from Alexandra Palace to Moorgate every 10 minutes. That worked but most trains were 3 coaches. The 2018 failed timetable moved them for a short period to every 15 minutes on both routes. Looking at the May timetable they have fixed the timetable and it is a real 15 minutes service from Moorgate - Alexandra Palace (I think it was 10 / 20 / 10 / 20 previously). I agree this should be satisfactory with the current loadings.
I think it was originally every 20 mins when the electric service was launched in the 1970s - it was sometime in the early 80s it went to every 30 mins - I don't recall it being every 20 after that (though if it happened after 2000 I wouldn't as I was no longer in the area).