Technology, Books and Other Neat Stuff

Judging from the planned service pattern to Terminal 5, the construction of the extension actually will require substantial reconstruction of the present loop tunnel.

The original Piccadilly Line extension to Heathrow was a standard twin track route, with one eastbound and one westbound track. When the Terminal 4 extension was constructed, it was built as a single track one-directional loop, deviating from the old westbound track west of Hatton Cross, and linking up to the eastbound track at T123. Since the loop was opened, the old westbound track has been largely unused. The reason that the whole of the route beyond Hatton Cross is closed this weekend will be to ensure that the westbound route is up to standard.

Now from what I can gather, the new extension to T5 allows a service that goes to T123 and then to T5. If the new tunnel branches off the loop, then presumably they will have to build a new westbound track from T123, with the present loop providing the eastbound track for the T5 extension. (If you're wondering why this is the case, the only alternative would be to make the section of the loop between the where the extension branches off and T123 bi-directional. Not only would this restrict the frequency of services on the T5 extension, but if you're happy with the idea of potential head-on collisions under Heathrow, well ...) I just don't think it's safe to be running trains through the loop while a new parallel tunnel is being constructed, hence they can't run trains on that section of the loop. But because the loop only works in one direction, that means they can't use the loop at all, hence T4 Piccadilly has to be closed. (I suspect much of the wholly new alignment will be built in the intervening period between T4 station and the loop reopening in 2007 and the new Terminal opening in 2008.)

So, there you have it. Makes sense to me.

I never did get round to testing my theory that taking the tube from Terminal 1,2,3 would be quicker than waiting for the shuttle bus

I doubt it, as you'd have to go out to Hatton Cross and then change on a train going back into Heathrow to achieve that journey. Taking the Heathrow Express from T123 to T4, on the other hand, should be a lot quicker.

am *not* taking big suitcases up and down the irregular stairs at Putney that I'd complain to HSE about if I wanted the station to actually be closed for months, or through the heaving mass of the Clapham underpass. do not enjoy pain! no, HE or a cab - there's only a couple of quid in it!