I'm pretty sure they have managed 3 trains in 10 minutes At Salem when they were running off schedule due to a train being behind schedule. Two in one direction and the other in the opposing direction.
BostonUrbEx wrote:I never suggested scrubbing GLX today. I'd say it should have been planned differently from the start, decades ago!This is even more disingenuous! The "Beyond Lechmere Northwest Corridor Study Major Investment Analysis" from 2005 quite literally scored LRT, BRT, and commuter rail modes against each other and crunched all the demand numbers in the appendices showing point-blank where native Somerville ridership does and doesn't get dispersed downtown. The existence of magical 1998 alternate-universe NSRL ribbon-cutting does not flip the travel patterns on their head from the Central Subway to the Waterfront/South Station. The CTPS data reaffirmed 100 years of established travel patterns on this corridor: they pour into Lechmere and go to Haymarket, GC, Park, and the stations along Boylston St. in huge numbers in addition to North Station. They even re-crunched the numbers based on presence of the Urban Ring changing the spread of linked trips around Cambridge, and it simply reaffirmed the original conclusion.
Go on the document archives on greenlineextension.eot.state.ma.us, start with Appendix F and work through the study docs from there, and prove the math is dead-wrong, upside-down, or backwards through your own number-crunching analysis. This project rests on burden of proof calculations so many levels deep that it can't be upended by throwing a couple stones from the sidelines and arguing-via-obscurity that a bunch of old-school planning dinosaurs weren't being "forward thinking" because reasons.
SHOW where the modal choice not made is superior for where people need to go, and what not-at-all-voodoo mechanism turns 100-year demand patterns onto an entirely different corridor.
I'm not convinced. Salem has inbounds scheduled within 10 minutes of each other while utilizing diesel locomotive-hauled sets, a track/signal system that could be improved, and all on a single track pinch point. There is a point in the day where Salem sees trains every ~8 minutes (including both directions, but remember this is single track, so with opposing moves that's even more impressive). Not to mention, the discussion at hand involved quad-track.And this factoid artfully tapdances around the key-most point I made. Mainline rail can absolutely pack headways close. It cannot, because of the more heterogeneous traffic profile (that gets MUCH more diverse post-NSRL when scaled to the Lowell Line), guarantee that every Urban Rail local throughout a given shift sticks as close to the advertised headway as a closed metro/tram system can. A longer-distance train is going to get more schedule padding on a slot, and will clip and shift the margins of that MU schedule by a couple minutes a couple times an hour. That puts schedule consistency outside the margin of error a metro/tram system would be able to hold.
Quad-tracks? What does that matter when you're still mashing into 2 NH Main tracks for the NSRL portal...then merging 2 NH Main, 2 Fitchburg, and 2 Eastern/Western tracks--each with their own hetereogeneous short and long-distance scheduling--into 4 tracks of the main bore. With all the associated interlockings, and the upstairs/downstairs splits from the retained surface terminals. The local tracks on the NH Main aren't hermetically sealed from the effects of slotting longer-haul traffic when they all engage each other in the Terminal District. They get their headway variability fileted in the Terminal District by what's got priority at any given moment. And this is where absolute frequencies will never end up meeting what the Green Line could provide, as well as being able to meet the shift-long consistency of the headways. Are pretty good frequencies achievable that way? Yes. Are those frequencies good enough to satisfy Somerville demand growth like the Green Line can? No...not even close, say the studied-to-death demand numbers. The two modes aren't interchangeable for that task because the NSRL is predicated on continued (or even expanded) existence of a hugely complicated union station terminal district in the CBD, while the Green Line for all its warts does not.
This is why first-world cities still segment their metro/tram and mainline rail modes by purpose even when coverage overlap on a corridor is semi-intentional. And why magic "Uni-mode" hasn't wiped the slate clean like all the BRT astroturfers and prophets of the DMU gospel said it would. Because well-planned transit systems don't pick the inferior tool for the stated job for proof-of-concept bragging rights. The NSRL can't move enough Somervillians often enough to where the highest percentages of them need to go to be in any way a drop-in replacement for GLX. Even in magic alternate universes where we started Link construction in 1995.
However, if you want to calculate what Jetsons-tech dispatching precision can do to close the gap at a technical level, go right ahead. But do not do that with one hand while feigning ignorance with the other on what the demand numbers are. Those have to be substantiated too. A narrower performance gap between RR and LRT modes doesn't mean RR mode "wins" when more people on this corridor still, after 100 years, need to get down the Central Subway corridor than need to get down the NSRL corridor and swapping the two means demand goes unmet. It means making more half-arsed compromises that don't address the very question being asked. The end result is little different than the intensity of belief in BRT-for-BRT's sake that dictated to Roxbury: "Your pleas for a one-seat from Dudley to the nerve center of the Big Four transfers are baseless because instead we're giving you the one-seat to the Seaport and Airport you never asked for, and that's better than nothing."