Overshooting/Undershooting platforms

[Deleted]

I've read in other threads how trains on the Victoria Line can overshoot the platform (requiring the use of an emergency brake) and how trains on the Central Line can undershoot (requiring the driver to take the train in the rest of the platform under manual).

However, those lines feature someone at the front of the train to take over from ATO when those events happen. The DLR doesn't. Do does the Train Captain have to make his/her way to the front of the train to work it manually, are the platforms long enough to compensate for overshooting, or does the DLR have some tech LU doesn't have?

[Deleted]

Not sure at all, it's just a guess :

Most of the time, the DLR runs much slowly than the Underground does, which means it can brake later into the platform, maybe more precisely. But I think the biggest difference is the weight : the DLR being much lighter than an underground train, it has less inertia, and, along with the slower speed, it helps acquiring less kinetic energy, which means less energy to dissipate when braking. This means that the train can be brought to a stop on a much shorter distance. In my opinion, but once again it's just a guess, the brake could be set to an almost constant value, and be applied at a fixed fixed distance from the stop mark depending on the speed.

[Chris M]

I don't know the reason for it, but in my experience the DLR hardly ever under or overshoots the platform - I've experienced the former just once and the latter never in all my DLR journeys. In contrast the Central line train I was on on Friday undershot significantly (at least 2-3 car lengths) three times between Debden and Stratford.

If the DLR does pull up incorrectly there is not much margin for error (about 0.5-1 door widths at most stations) except in the case of a 2-car train in a 3-car platform. If manual correction is required then the staff member must make their way to the front. If there are known adhesion issues in an area though then AIUI control will tell the PSA to be at the front in advance (although this is not the only reason to do that).

[Chris M]

I don't know the reason for it, but in my experience the DLR hardly ever under or overshoots the platform - I've experienced the former just once and the latter never in all my DLR journeys. In contrast the Central line train I was on on Friday undershot significantly (at least 2-3 car lengths) three times between Debden and Stratford.

If the DLR does pull up incorrectly there is not much margin for error (about 0.5-1 door widths at most stations) except in the case of a 2-car train in a 3-car platform. If manual correction is required then the staff member must make their way to the front. If there are known adhesion issues in an area though then AIUI control will tell the PSA to be at the front in advance (although this is not the only reason to do that).

[trt]

And the Jubilee line has to be spot on!

[crusty54]

the whole of the DLR is set up for 80 km per hour operation now - when it is safe to do so. Hardly slow.

[alholmes]

They undershoot occasionally - could be by as little as 6-12 inches, and it usually requires the Train Captain / PSA to go to the front. I've overshot only twice in 25 years on the DLR, both times at All Saints. On one occasion the Train Captain gained permission to reverse. On the other occasion, after consulting with control, we were just sent forward to the next station, so alighting passengers had to double-back.

Not long after the system opened, I was on a very lightly-loaded train to Stratford. We arrived, but no-one opened a door very quickly and almost immediately the train got the 'Ready to Depart' indicator and started moving back to Bow Church (this was pre-Pudding Mill Lane existing). So all passengers need to alight at Bow Church and change platforms - missing the next train to Stratford in the process!

[Chris M]

Jul 17, 2012 23:07:37 GMT crusty54 said:

the whole of the DLR is set up for 80 km per hour operation now - when it is safe to do so. Hardly slow.

True, but I think that speed is only attained Shadwell-Bank and King George V-Woolwich Arsenal, stations being too close together elsewhere, and station approach speeds are not that high even there. The braking profile is very different to tube trains though - compare the DLR and Jubilee approaches to West Ham Stratford-bound (where the stopping points are the closest to level). At some places the DLR ATO will slow to nearly a stop before accellerating a bit to reach the stopping mark, Shadwell westbound comes particularly to mind.