Quote:
Originally Posted by jmecklenborg
If the red line is separated from the purple line and made to continue south on Vermont, then in theory the purple line could be made to split into three branches at Westwood Ave. One would head north to UCLA and the valley, another would turn south to LAX, and a third would continue westward under Wilshire to the VA and a future Santa Monica extension. A fourth route would be a north/south train between the valley and LAX.
What I just described would put 3 trains on the subway between Westwood and Union Station. BART does this with four trains, but there are many problems associated with it during peak hours, and a second transbay tube no doubt would seek to split the four routes between the two tubes.
One tiny operational advantage would be that the physical connection between the Wilshire Subway and the Sepulveda line would be made at some point east of the Westwood station, meaning that station could be skipped, creating a 1-station skip-stop. So what I mean is if you were heading south from UCLA your first purple line station could be Century City. Doing this would of course require flying crossovers from both the north and south and there is no provision for this in the purple line project, which is already under construction and can't be changed at this point.
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I knew BART was going to be mentioned but I don't think it is very useful comparison. BART shares a common transbay tube but the lines spread out and ridership drops pretty fast outside the trunk line in between SF and Oakland - so the network design makes sense because the outer branches can get by with 1/3 or 1/4 of the frequency of the trunk section between Oakland and Daly City. Sepulveda and Wilshire lines are different. There won't be a low ridership branch to Antioch or Richmond - the entirety of Sepulveda line and Purple line are trunk lines.
Red line separation from Purple line is just a concept. Vermont subway probably won't happen in the next 25 years. But I agree that if the two lines are separated, the purple line continuation to the Valley or LAX is more feasible. But in that time, Purple line could also get extended to Santa Monica. Branching Purple line into 3 branches at Westwood is not ideal and creates an imbalanced schedule and artificially long headway - now you have to wait for every 3rd train to come to get to your destination on one of the branches.
Ironically, if Purple line ended at Westwood, this would be easy to do... the line simply branch north or south. But the line goes to VA hospital (and potentially Santa Monica) so realistically, you can only branch north or south at Westwood, not both (the other branch has to continue west). However, this creates its own problem because now Sepulveda line has uneven service north and south of Wilshire.
So we are basically back to my original point... much simpler and efficient to run two high frequency line rather than trying to interline, which means one of the branch of Sepulveda line will see 50% less service. I much rather both line run at 2 min intervals and transfer at Westwood then having to wait 4 or 6 min to get on the Wilshire to LAX train or Wilshire to Valley train. This may be acceptable way to run BART because not many people (comparatively) are going to Millbrae or Milpitas vs. Oakland but it won't be acceptable in LA where all the existing and potential stations on Purple and Sepulveda line are in the high ridership zone instead of far flung suburbs.