With respect, no it isn't.
On the "down", the StanEx leaves Liv St with a clear track ahead of it and is timetabled to take 12 minutes to reach Tottenham Hale. There really isn't any time lost during this phase. Likewise on the "up", once the StanEx is in the platform at Tottenham Hale whatever service was running ahead of it will clear the line quickly and not cause delays to the following StanEx. Granted there are times when a late running Chingford train will result in a StanEx being held on the cord between Coppermill and Clapton Junctions and some StanEx services are timetabled to follow a slow train from the Seven Sisters line into Liv St, but most are unimpeded.
Where the time savings can be made are further down the line.
On the "down" the StanEx usually finds itself behind something slower and time is built-in to allow for this. It's usually on approach to Broxbourne when following Hertfords or slow Airports (from Stratford), or Bishops Stortford when following a Cambridge. All StanEx runs on the "down" have an additional 2 minutes time between Harlow and Bishops Stortford so that the crossings at Sawbridgeworth and Spellbrook can be synchronised with trains on the "up", and some have up to 4 additional minutes. On the "up" it's usually somewhere around Cheshunt where the slower services are caught. Provided it's an "up" Cambridge it's not too bad but a late-running "up" Hertford can really cause problems.
We know all about this and can "time" a service to minimise the impact of it. However, there isn't much that can be done to accelerate the service when the StanEx has to share the tracks with so many other services. It's pointless trying to increase the linespeed while this situation exists as we can't even make full use of the existing linespeeds. If I've stopped at Harlow Town on the "down" I will only get the train up to 65mph and then coast from the river bridge north of Sawbridgeworth so that the speed bleeds away until I'm down to 45mph for the restriction through Bishops Stortford. This keeps me perfectly to time and uses up the 2 additional minutes almost to the second and also means I rarely get stopped for Sawbridgeworth or Spellbrook crossings. As Flywaver has already said we could massively accelerate the service now if only we could get a clear run. Increasing the linespeed will make no difference at all.
O L Leigh
'Downs' are indeed mostly timetabled at 12 minutes.
By quoting 'Tottenham Hale to Liverpool Street', I was referencing the 'up' services.
My morning train is the 0615 ex SSD. It is timetabled at 16 minutes TH to LivST, but frequently is nearer 20. One of the worst trains in the morning peak is the 0700 ex SSD which is timetabled at 21 minutes for that leg!
My post and reference was really following on from my earlier thread about how the journey time has stretched over the years - in the days when the StEx used to be timetabled at 41 minutes and regularly did it in 38-39, the LivSt to TH leg was timetabled at around 8 minutes, so has stretched by around 50%, to near 100% in some cases.
In
relative terms (i.e. the distance between TH and Liv St is probably less than 20% of the StEx route, but with some services can take around 35% of the total journey time) this is a massive increase.
As I mentioned earlier, the propaganda says average journey time is 46 minutes (how come they have not been censured for that blatant porkie?), in reality it is between 52 and 59 minutes depending on the service.
I do however totally agree that this is largely down to extra traffic on the line, which has grown considerably over the years, and must now be pretty much at capacity.
There have been many versions of the timetable over the last 15 years or so since the number of total services on the line were increased, and there have been many absolute scheduling howlers, such as where the StEx left LivSt right behind slow stopping services.
In NEx's defence, given the constraints of too many trains going in and out of LivSt at peak times to ever be able to go back to the heady days of 41 minute StEx services, the current version of the timetable is probably the best there has ever been regarding scheduling fast and slow services in relation to each other. The StEx services went through an absolutely diabolical period of timekeeping in the five years or so after the Hatfield crash, and when the timetable was radically altered to put Stortford and Harlow stops in, then going to the 15 minute timetable, hardly any StEx services ran to timetable.
As you mention, there is 'padding' built in to the working timetable, but sadly part of this is probably to allow buffer time so the PPM figures do not result in financial penalty.
Acts of God, scheduled maintenance overruns and plagues of locusts apart, the services generally run pretty much to timetable these days

- (although StEx still has pretty much the worst timekeeping statistics of all the services at LivSt).