What Line has the closest headway's??

Surely it will be a line with ATO as trains on these lines can run a lot closer to each other as it is safer. So its either got to be the Central, Jubilee or Victoria Lines. But then the Jubilee seems to have a reduced train frequency compared to the Central and Victoria as it is not as busy with gaps being up to 4 minutes so I would say either the Central or Victoria

I'd say the Vic must have some of the closest headways, bearing in mind how close the trains can get to each other!

If it's 'actual' then on the Central Line at Stratford it's been seen for one train to leave whilst another pulls in..justabouts.

Thanks for injecting some actual facts Reg

Historically, was the winner of this acolayde the District/South Circle? Or perhaps before that the Bakerloo? Frequency has definitely come up on the forum before somewhere...

There are certainly some signals on the northern half of the circle line which are designed with a headway of 40tph, though the actual throughput is limited by the signal with the lowest headway.

It's actually a bit more complicated than that. The overall limiting factor on headway may be other things like the dwell time at the busiest station (say Victoria) or the ability of the terminus to turn round trains (say Brixton).

Also, the top speed of a route will affect the throughput. As the speed rises, so does the braking distance. As the braking distance rises, the spacing between trains becomes greater.

It is also interesting that, when multi-home signals were being installed on the Underground in the early 1920s, they discovered that 3 homes was the useful limit. Any more didn't help the frequency. Even speed control didn't help much unless the dwell time was extended.

If I could find the thread, I think we'll see we've done all this before.

30 tph is the limit really any more trains is just going to cause bunching up
Also there is less recovery time, when things go wrong

Well obviously i am not a railway controller! But look at the central line which could in theory run more than 30 TPH but can't due to liverpool street dwell times.
For Brixton for quick turnarounds i have an idea why dont they just have a spare driver ready sitting in the opposite end cab to set the train off at terminus? Or they will just have to sprint to the other side of the train however I doubt due to heath and Safety!
When things go wrong you will have trains stuck in tunnels rather than in platforms.

jardine01 - Please stop commenting on things you either know nothing about, or cannot justify.

Aside from junctions and termini, headways between trains are affected by platform reoccupation time, dwell time, and operating margin.

Operating margin and variations in dwell time make the difference between theoretical shortest headways, actual headways, and timetabled headways. Even platform reoccupation time varies between stations.

The platform re-occupation on the Central Line's busier stations is approx. 60 secs. Add a typical peak dwell time of 35 seconds, and that leaves 25 seconds operating margin for the timetabled 120 secs headway. However, when bunching occurs trains can often be observed running at 85 seconds headways.

I don't know the exact platform reoccupation times for the Victoria Line and Jubilee Line, but would expect the Victoria Line to have platform reoccupation times around the 50-60 secs range, and the Jubilee to be in the 40-50 secs range.

By the way, Moscow Metro can operate longer 155m trains at 95sec timetabled headways, and Metro de Santiago will soon operate 120m trains at 100sec timetabled headways. Both operate with only around 15 secs operating margin. By the way, both do occasionally experience trains catching up with the trains in front and stopping between stations - it's a fact of life if you want to operate metros at high frequency!

Thanks for the info.

46 secs is pretty impressive for a fixed block/DTG system. The traditional (and long removed) speed controlled/multiple home setups were designed for approx. 52 secs.

I would be interested to know the platform reoccupation times on the Jubilee using Seltrac.

If they did it then why cant it happen now? Apparently the circle line ran 40TPH is this true?

The terminus loop probably helped, and short train consists.



For starters, there was higher capacity signalling than most current lines (except Victoria and Jubilee). More aggressive driving strategies (i.e the odd SPAD was not really an issue). It could be questioned as to what effects the frequency had on reliability, journey times, and stock requirements. A few people on this board may be able to fill us in here.

Driving techniques were variable. There were some drivers who got very good at balancing speed and braking techniques to get the best performance out of the system but they were more the exception than the rule. The odd SPAD was accepted as the system doing the job it was supposed to do.

Under the old signalling with anything over 32 tph, you would generally lose 10 minutes or so at the end of every peak. They would reform us on the Circle by dropping back train numbers so train 171 became 172 or 173 etc.

When speed control was introduced in the 1950s, it was said to save an additional 10 seconds per train and allow an increase of 5 tph through the District Line at peak times to give 44tph. This was based on lower speeds, a smaller margin and a short starter overlap.

Articles on speed control signalling have appeared in Underground News – “Speed Control Signalling” written by me for UN 414, June 1996 and “33TPH Service Headways and Train Working” by Robert Hammond, which was published in UN 488, August 2002.

At the risk of repeating myself, the old idea that we should get 40+ tph on the Underground today surfaces regularly. It won't happen. We have longer trains, higher speeds and very restrictive signalling design rules. We are also running most lines with some excessive dwell times at central stations and we have terminal protection just to further restrict throughput.

In my opinion, pushing for any more than 30tph under London conditions is not sustainable. The main advantage of the new DTG-R and TBTC signalling is faster recovery from delays.

The terminus is just one problem. If you look at Brixton, it's not the turnround time of trains that restricts the capacity, it's the time taken to clear the high speed crossovers and reset the route. I believe that the completion of the asset replacement programme should help to increase throughput. If that was to allow say, 33tph, then the extended dwells mentioned by racka earlier, would be the restricting factor. Timetabling generally has nothing to do with it.

Actually, squeezing a few more tph isn't necessarily the objective. The objective is to carry the people who want to travel. In London, there are just too many people for the existing lines to carry. More lines are needed. Crossrail will help but at least another SW-NE line is needed now.