05-05-2022, 12:23 PM
(05-05-2022, 03:17 AM)danbrotherston Wrote: I *do* think there is an interesting inversion of thinking that nobody really talks about which is the concept of a double track line with choke points. I'm not sure how this impacts scheduling, but if you widen the track to double tracks everywhere except the most expensive areas (bridges, tunnels, downtown) can you achieve most of the benefit of double track, with a fraction of the cost? Or do you really lose most of the benefits. I'm not really sure, and I don't think anyone can really answer the question definitively without actually studying it, scheduling is another problem that humans aren't very good at (mind you, neither are computers). FWIW...there is a BRT line in Gatineau that uses this concept. It re-uses an old single track railway bridge to cross the...Gatineau? river. Buses arrive and must wait for the bridge to be clear of oncoming traffic before proceeding. FWIW...again, this is something that works better when you aren't sharing with freight trains.
I had not heard of this bridge, so looked and sure enough:
https://goo.gl/maps/GEccY3ATXRSmiAh48
You have the right river, and indeed the BRT runs parallel to a rail line which looks to me like it is out of service but still there. At the bridge, both directions of the BRT merge onto the single track; with appropriate protection one could have two-way rail and bus traffic. Incidentally, the rail line is the same one which used to continue across the Ottawa River and whose right of way is now used for the original O-Train on the Ottawa side.
I think for intermediate levels of service, this kind of concept can make a lot of sense. Instead of insisting on double track absolutely everywhere, leave some narrow areas. This also gives a turnback location for free. Even on the LRT this could have been done, for example on King between Allen and the Uptown station. The LRTs almost always meet at Allen so north of that location there is only one vehicle on the two tracks at a time. Of course, as you point out, as soon as something goes wrong it can cascade to the other direction; and at some point with increasing frequency it would start to cause significant problems.