Crazy Transit Pitches

[Riverside]

I fully agree with everything @Teban54 wrote (except maybe the point about that particular extension into Revere -- I'm not convinced that the Eastern Route is the best alignment, but I agree with that overall point that, once freed from the obligation of circumferential service, the possibility of extension to the northeast becomes much more obvious).

I don't think people think this way when taking the train, and basically everyone would absolutely take the UR from Sullivan to the Airport. People don't think about how many miles the train is going. Nor is it even easy to tell, especially because the system diagram map would likely show the UR route as a roughly straight line from Sullivan to the Airport. And even practically, going an extra mile on a train isn't a big deal. You just sit there a few minutes. Compared to the variable amount of time a transfer adds on, it's basically a wash. Plus the OSR option means no hauling luggage up and down stairs, or trying to get a new seat on the second train. If the UR has nice new, comfortable, reliable trains and stations, then I would expect people would go from Sullivan, Kendall, and Cambridgeport to the airport on the UR rather than whatever transfers. It would be more comfortable and convenient.

This is one of the trickiest questions to answer, and may well be impossible to answer with satisfactory confidence. I agree with @Teban54's points, but will add a couple more.

basically everyone would absolutely take the UR from Sullivan to the Airport

I think everyone would do it once. And then never again.

Assembly <> Airport via Grand Junction is 4.4 miles. At 12 mph (which I think is potentially optimistic), that is 22 minutes. On today's Orange and Blue (with all of their problems), the same journey takes anywhere from 27 to as little as 23 minutes. The transfer at Assembly will probably be less friendly than at Sullivan, which makes the comparison even worse: 4.9 miles at 12 mph yields 24.6 min on Grand Junction from Sullivan, while Orange <> Blue ranges from 25 to 20 minutes.

(Add on top of that: Grand Junction frequencies are almost certainly going to be [slightly] lower than Orange and Blue, so that transfer will be more brittle.)

And on top of that, even if people don't count stops or measure route miles or calculate travel time, Google Maps and similar platforms do, which is going to increasingly drive behavior in the future. And I think Google will not look particularly favorably at a Grand Junction route; at best, like you said, it's a wash, so probably Google will send some riders one way and others the other.

Plus the OSR option means...

Well, so, there are really four different proposals we're talking about here:

• WITH dedicated Chelsea Creek crossing and WITH direct service to Central Parking/the Terminals
• WITH dedicated Chelsea Creek crossing and WITHOUT direct service to Central Parking/the Terminals (end at Airport station)
• WITHOUT dedicated Chelsea Creek crossing and WITH direct service to Central Parking/etc
• WITHOUT dedicated Chelsea Creek crossing and WITHOUT direct service to Central Parking/etc

As long as shipping traffic in Chelsea Creek remains the same as today (and I have questions about that, but will circle back), then any of the alts without a dedicated crossing will be prone to semi-random 20 minute delays, which will totally negate any allure that might be held by a line that looks faster on the system map. (Like I said, folks will try it once, and never again.)

Likewise, for all of the alts without direct service to Central Parking/the Terminals, any benefits of an OSR go out the window: your choices are either Orange -> Grand Jct -> Massport shuttle, or Orange -> Blue -> Massport shuttle.

So, we're really only talking about one alternative that accrues enough benefits to plausibly divert riders away from downtown, and it's the one that is by far the most expensive.

I still think cross-Creek service is valuable! I just don't think it should be predicated on the idea of reducing Orange <> Blue transfers at State.

 

[Riverside]

From 1933 to 2021, the highest elevation above ground for a rapid transit station was Smith-9th Streets in NYC, at 87.5 ft. Here are some photos (source 1, source 2). The "170 ft Eastern Ave station" will be almost twice as tall.

For anyone who might be familiar with it, Brown University's Sciences Library on the East Side of Providence is 180 feet tall, so a pretty close comparison for how high a Chelsea Creek crossing would need to be. Google's 3D images show how it towers over the surrounding neighborhood (which mostly built up to, I dunno, 4-6 stories):

Even my proposal of, essentially, a transfer station that spans the Creek with a very high pedestrian walkway in the middle would still be a massive project.

 

[Riverside]

Those lift statistics are interesting though. If you could build high vertical-lift bridge high enough to clear the tugboats, most of the problem would seem to be eliminated with less than one opening per day. It's probably expensive though, which is where the Massport dollars could come in handy. To my point the other day about building Elevated on already-blighted areas, you could probably snake across 1A like you have even with the height restrictions to a station where the police station is like the original APM concept had.

It's a lot more than that. There were 7 openings on the 21st, for example, a couple were 20+ minutes long. As long as Chelsea Creek is open for shipping any elevated rail or APM line is probably a no-go.

I want to come back to this. @737900er your point, if I'm understanding right, is that a new bridge might not have to be as tall if it can still clear tugboats when in the lowered position, only needing to raise when the tankers come through, right?

Link to the fact sheet, apologies for omitting earlier.

@F-Line to Dudley, I think you had some info at one point about the varying clearances needed for different types of ships; do you know what the clearance would need to be for a tugboat?

Because yeah -- if the openings can be limited to once a day, then this would be much less of a problem.

 

[737900er]

I want to come back to this. @737900er your point, if I'm understanding right, is that a new bridge might not have to be as tall if it can still clear tugboats when in the lowered position, only needing to raise when the tankers come through, right?

Yes, say you cross Chelsea Creek with a movable bridge where the deck is usually 60' AMSL and raises to 175' for openings. For most vessels the LRT bridge would remain fixed and the Chelsea Street bridge would open, except for the tallest ones where the tankers need the full clearance. Sort of like how the Lechmere Viaduct crosses over anything that needs the other bridges to open (and how I assume it used to work when it was a functional movable bridge). As the fact sheet says, most of the tugs pass before the bridge has even reached its full height. As you can see in these photos I saw on UHub/Mastodon the other day, the tugs are substantially shorter than the tankers. I have no idea about the barges, and I admit that I know very little about maritime stuff in general.

I'm not sure how tall 1A is around the Neptune Road crossing, but if you're already elevated there might be clearance to snake over it even though it's right at the 33L centerline.

 

[ritchiew]

Well, so, there are really four different proposals we're talking about here:

• WITH dedicated Chelsea Creek crossing and WITH direct service to Central Parking/the Terminals
• WITH dedicated Chelsea Creek crossing and WITHOUT direct service to Central Parking/the Terminals (end at Airport station)
• WITHOUT dedicated Chelsea Creek crossing and WITH direct service to Central Parking/etc
• WITHOUT dedicated Chelsea Creek crossing and WITHOUT direct service to Central Parking/etc

As long as shipping traffic in Chelsea Creek remains the same as today (and I have questions about that, but will circle back), then any of the alts without a dedicated crossing will be prone to semi-random 20 minute delays, which will totally negate any allure that might be held by a line that looks faster on the system map. (Like I said, folks will try it once, and never again.)

I see. I think I'm mixing up or missing some proposals across a couple of threads here.

But what I'm mostly missing is why you wouldn't just put a tunnel under Chelsea Creek? That doesn't even seem like a "crazy" transit pitch. That's just what you'd do if you built an Urban Ring. My guess is you'd do an immersed tube tunnel, like they did for the Pike and Silver Line across Fort Point Channel. Chelsea Creek is even a little narrower with far less existing infrastructure around. There are plenty of sites along the creek to potentially build the tubes. How is this even a questions for a "crazy" transit pitch?

 

[JeffDowntown]

I see. I think I'm mixing up or missing some proposals across a couple of threads here.

But what I'm mostly missing is why you wouldn't just put a tunnel under Chelsea Creek? That doesn't even seem like a "crazy" transit pitch. That's just what you'd do if you built an Urban Ring. My guess is you'd do an immersed tube tunnel, like they did for the Pike and Silver Line across Fort Point Channel. Chelsea Creek is even a little narrower with far less existing infrastructure around. There are plenty of sites along the creek to potentially build the tubes. How is this even a questions for a "crazy" transit pitch?

In a real Urban Ring future world, wouldn't you take the same approach for the Mystic crossing, and end up with a Sullivan Under station?

 

[Riverside]

Yes, say you cross Chelsea Creek with a movable bridge where the deck is usually 60' AMSL and raises to 175' for openings. For most vessels the LRT bridge would remain fixed and the Chelsea Street bridge would open, except for the tallest ones where the tankers need the full clearance. Sort of like how the Lechmere Viaduct crosses over anything that needs the other bridges to open (and how I assume it used to work when it was a functional movable bridge). As the fact sheet says, most of the tugs pass before the bridge has even reached its full height. As you can see in these photos I saw on UHub/Mastodon the other day, the tugs are substantially shorter than the tankers. I have no idea about the barges, and I admit that I know very little about maritime stuff in general.

I'm not sure how tall 1A is around the Neptune Road crossing, but if you're already elevated there might be clearance to snake over it even though it's right at the 33L centerline.

Yeah that makes sense, appreciate you clarifying. Eyeballing those photos, it looks like the tugboats are about 4 stories tall, so 60' above the water level probably would do it? That would require something like 1200' of incline (at a 5% grade), which would stretch to about Bellingham St to the north and something like Bremen St & Chelsea St to the south. That's still not trivial, but definitely is better than what would be needed for 170'.

I see. I think I'm mixing up or missing some proposals across a couple of threads here.

Honestly I think that the whole discussion is sliding back and forth among those four proposals, so it's not just you.

I see. I think I'm mixing up or missing some proposals across a couple of threads here.

But what I'm mostly missing is why you wouldn't just put a tunnel under Chelsea Creek? That doesn't even seem like a "crazy" transit pitch. That's just what you'd do if you built an Urban Ring. My guess is you'd do an immersed tube tunnel, like they did for the Pike and Silver Line across Fort Point Channel. Chelsea Creek is even a little narrower with far less existing infrastructure around. There are plenty of sites along the creek to potentially build the tubes. How is this even a questions for a "crazy" transit pitch?

Yeah, it's a fair question, and I don't know the ins-and-outs of tunneling as much as I wish I did. You'd need to contend with an elevation change of a similar magnitude as a 60' bridge, so it seems in some ways like you'd still need to pour the same amount of concrete, whether into the ground or into the air. But I defer to others more knowledgeable than me.

That all being said, I still come back to this:

But that brings up another point: Splitting the "Urban Ring" into two along the Eastern Route really isn't a bad thing - it will already be used as such.

If we assume very few riders will go from Assembly all the way to Airport, then the demand pattern along this stretch really serves as two routes:

A Chelsea Creek crossing will be load bearing for Chelsea <> Airport and partially for Chelsea <> Seaport, but I maintain that the circuitous route via Everett means that it's never going to be load-bearing for Sullivan <> Airport, or Orange <> Airport (see catch-22 caveat below). Chelsea <> Airport demand is obviously real, but hardly astronomical at the scale needed to justify an expensive bridge.

And, somewhat parsimoniously, the stuff that makes a Grand Junction LRT line work well -- existing ROW, partial existing grade sep, ROW goes basically to the front door of the necessary places -- is markedly less present south of Chelsea Creek. The ROW is sorta still there through Airport, but not grade separated, and definitely not fully intact. And then getting from Airport to the actual airport is a whole separate problem.

So, I maintain that the best all-around solution here is a modern LRT line as far as Eastern Ave, with a BRT line, ducking in and out of mixed traffic, meeting it (and/or supplementing it with a short extension into Chelsea proper). Something like this:

EDIT: Forgot my catch-22 caveat: the only way this route becomes load-bearing for Orange <> Airport is if the expensive grade-separated Creek crossing gets built... but the crossing won't get built if there isn't demand for it. So, my thought would be to build the LRT to Eastern Ave, live with BRT as the First Gen option, and then build an expanded people-mover, inclusive of direct service to terminals and to a transfer station at Chelsea Creek. Maybe that people-mover is normal LRT, and thus could be an extension of the Grand Junction line; maybe that people-mover is a bespoke monorail build stretching from Chelsea Creek to the terminals and maybe to the ferry terminal.

 

[Ayo]

Theres a cable car system in Santiago Chile that has dedicated bike cars so Luggage might be a solvable problem. I haven’t found out how they do that though in my admittedly little searching.

Santiago Cable Car - Wikipedia

en.wikipedia.org

/edit/
I found a video for how it works, not sure how practical it would be

 

[bigeman312]

Theres a cable car system in Santiago Chile that has dedicated bike cars so Luggage might be a solvable problem. I haven’t found out how they do that though in my admittedly little searching.

Santiago Cable Car - Wikipedia

en.wikipedia.org

/edit/
I found a video for how it works, not sure how practical it would be

It’s a somewhat simple concept that’s implemented in resorts here in the United States. Some cabins have passengers, while other cabins are just for cargo, like bicycles.

There are resorts here in New England where you can see a similar concept in practice. For example, Killington Mountain Resort has the most uphill capacity among ski areas in Eastern North America. This is a metric that would be relevant in our discussions of urban transport, here. They accomplish this feat with 21 lifts:

• 4 surface lifts, which are low-speed, low-capacity, and not relevant for this discussion.
• 17 are aerial lifts, in the broad category of aerial cable transport we have been discussing here:
  • 14 are chairlifts, for which open chairs (what some outside of a ski setting might see as akin to a “bench”) are attached to the cable. These chairs carry 2-6 passengers each depending on the chairlift, in Killington’s case.
    • On chairlifts during the ski season, you don’t typically carry any luggage larger than a backpack, which you are required to take off and hold on your lap in front of you.
    • 2 of Killington’s chairlifts, and many chairlifts at ski areas across the region, are converted to serve mountain biking in the summer. Some of these chairlifts are equipped to hang bicycles off the back. Some replace half of the chairs with bike racks, so the bicycles ride up by themselves.
  • 3 are gondola lifts, like we’ve been discussing here.
    • Before boarding a gondola lift, you are generally required to remove your skis or snowboard and store them on the outside of the cabin, where they sit in a simple storage bin.
    • 1 of Killington’s gondolas, and some other gondolas at ski areas across the region, are converted to serve mountain biking in the summer. Some of these have the same setup as the one linked in the video above, which is to have a mix of cabins and bike racks. Some, like the K1 Gondola at Killington, simply convert the ski/snowboard storage outside the gondola to bicycle storage in the summer.

 

[Riverside]

(Damn, I'm learning a lot about gondola & aerial lifts, and about maritime stuff! This is so cool!)

 

[Teban54]

(Of course, I was in the middle of writing this comment when I was interrupted by a 4-hour lunch and conversations with a colleague, and I came back to like 10 more comments.)

For this comment, I'll use "Day Square", "Central Parking" and "Logan Terminals" to refer to BL Airport station, a single centralized stop near the terminals, and 5 separate stops at all terminals, respectively. "Airport" refers to a possible choice of terminating Urban Ring among one of the three.

The other thing frequent users are aware of is the convenience of the transfer, particularly with luggage.

Orange to Blue at State is not a great transfer with luggage. At least one direction requires stairs (IIRC). And the station is really spread out.

I agree with the issues of OL-BL transfer (the walkway to southbound OL at State in particular is ~580 ft long), but this is something that highly depends on the Urban Ring's design, especially at Airport.

Day Square completely depends on where you place both the UR station and the APM station. In the worst case, as @737900er suggested, you'll have to go up, then down, then up. Central Parking has a 10-min walk to terminals (even with moving walkways, that's still far). Logan Terminals is seamless for riders, but I've already discussed the political (and even route design) issues. Realistically, in a world with an APM, Day Square is probably the most likely option until there's political will for another cross-harbor tunnel.

The OL-UR transfer is better, but still with caveats. The transfer at Assembly, if any, will likely involve a walkway that's not much better than State. Riders looking for convenience will end up in Sullivan (longer ride), and while Sullivan itself will likely have side-by-side platforms, riders will still need to go upstairs and downstairs (with the OL platform lacking bidirectional escalators).

(And if you're considering lines west of OL, now the Urban Ring transfer totally loses. Government Center and the new Charles/MGH are easy transfers, while East Somerville, McGrath and Kendall/Tech Square will likely not be.)

Those OSRs look pretty competitive to me. 11 stops directly or 9 stops with a transfer in the middle? That seems basically the same to me. If I had luggage, I'd opt to skip the transfer, probably. The only one on your list that is less competitive is Kendall, sure. But then there is the proposed UR stop in Cambridgeport, too. I'd probably ride that one seat to the airport, all 16 stops, rather than do 2 transfers. Especially if the transfer at Kendall is a 1/4 mile walk to the Red Line. With luggage.

The problem is that the majority of riders do not enter the rapid transit system at Sullivan, East Somerville or Kendall (especially the last two). They enter at places like Wellington, Malden Center, Gilman Square, Medford/Tufts, Union Square, Central, Harvard, Davis, etc. The combined demand from all these far outweigh neighborhoods on UR itself like Cambridgeport.

Suppose Urban Ring stops at Day Square. Sure, a Sullivan rider (e.g. from bus transfers or the East Somerville neighborhood) will compare:

• Urban Ring (one seat ride)
• Orange Line - Blue Line

But a Malden rider will compare the following, which erases the biggest advantage of Urban Ring - the OSR:

• Orange Line - Urban Ring
• Orange Line - Blue Line (likely fewer stops, shorter distance, and shorter travel time as @Riverside showed)

That's exactly why I said the T104 bus will likely prove to be more useful than Urban Ring for airport riders. And I don't think I need to even start doing the GLX and RL comparisons.

Not to forget: people may go somewhere else on the Blue Line that's not Airport! For someone going to Orient Heights or Revere Beach, now UR totally loses out due to back-tracking at Day Square.

So the question becomes: Is it worth figuring out the engineering and $$$ challenges for a better Chelsea Creek crossing, so that people boarding from Sullivan buses/neighborhoods and Cambridgeport have a more convenient ride to Airport for the couple times per year that they need it?

But as a basic premise here, do people count stops to choose subway routes? I don't think I've ever done that in any city I've been to. I generally look at a (non-geographically accurate) system diagram and see what looks most direct. Nowadays most people probably use Google maps or something similar. If there are multiple options that take roughly the same amount of time, people take whichever looks easiest, or whichever train shows up first. I'm not sure people generally count stops.

On the contrary, I've seen plenty of people in highly complicated rapid transit systems (think of those with 10-20 lines in Asia) counting stops in front of station maps. (But yeah, that's a minor point.)

But what I'm mostly missing is why you wouldn't just put a tunnel under Chelsea Creek? That doesn't even seem like a "crazy" transit pitch. That's just what you'd do if you built an Urban Ring. My guess is you'd do an immersed tube tunnel, like they did for the Pike and Silver Line across Fort Point Channel. Chelsea Creek is even a little narrower with far less existing infrastructure around. There are plenty of sites along the creek to potentially build the tubes. How is this even a questions for a "crazy" transit pitch?

I think everyone agrees that a tunnel under Chelsea Creek can certainly work in a world with unlimited budget. However, it circles back to the question I just asked above: cost-benefit analysis.

While "cost of 170' bridge vs. tunnel" is a separate question, regardless of the method of grade-separation, it needs to have enough usage to justify it. Which is exactly my original point: I'm not saying it doesn't have merit or isn't worthwhile enough (it can absolutely turn out to be), but the benefits of a grade-separated Urban Ring route to Day Square may be far smaller than it might seem on first glance. And as @JeffDowntown seemingly implied, the cost of such a tunnel may also be used for a more direct Sullivan-Day Square (or Maverick) connection via Charlestown, which brings more benefits to riders doing OL-Airport, GLX-Airport etc, and is equally capable of being extended to Central Parking or Logan Terminals.

We need a deeper understanding of the corridor, rather than "oh it connects Sullivan, Everett, Chelsea and Airport, so we're good", which likely overestimates the practical benefits. In particular, we shouldn't conflate the "radial" needs of Everett and Chelsea with the circumferential needs of a faster connection between OL and BL. And while the Grand Junction Urban Ring can succeed at doing the former, I think that too often people assume its success will come from the latter.

 

[Teban54]

I think something that will be 20/20 hindsight in about 15 years from now will be a very densely built up Everett between Encore and through downtown Everett up Broadway, especially along RBP. Right now, RBP and the rest of 16 is car centric, backed up at rush hour and weekends (from Revere to Fresh Pond), being developed in a very dense fashion now (Stop and Shop Redevelopment I'm looking at you), will be transformed through the gas tanks project and Everett is a very dense core with a working class, transit-dependent community, which is probably one of the more YIMBY cities around. If anywhere might be a candidate for needing it badly while building for the future, all MA legislative processes aside, I would think the dense blotch of Everett incoming is a really good one. I am not sure - if we're being crazy - sure, some type of feasible BRT is probably still crazy because of the difficulties of building around 16 and Broadway in Everett - but personally I don't think BRT will catch on enough to help. Personally, in my transit fantasy world, elevated concrete lines would catch on more in Greater Boston like other metro areas.

I certainly agree with Everett's potentials for development. In any world (even a very realistic one), an Urban Ring route through Everett (Sweetser Circle) will likely be built regardless of Chelsea Creek crossing, as LRT (or possibly HRT) from Chelsea/Eastern Ave to Sullivan and further west. Plus, it's one of the only logical locations for a yard. So in the long term, Everett won't be completely reliant on BRT.

(Whether Sweetser Circle is adequate in serving Everett is another question, but any options to bring transit north of Sweetser Circle has its own problems and tradeoffs. In the mean time, I think constructing a bus terminal at Sweetser Circle is worth looking at.)

I want to come back to this. @737900er your point, if I'm understanding right, is that a new bridge might not have to be as tall if it can still clear tugboats when in the lowered position, only needing to raise when the tankers come through, right?

Link to the fact sheet, apologies for omitting earlier.

@F-Line to Dudley, I think you had some info at one point about the varying clearances needed for different types of ships; do you know what the clearance would need to be for a tugboat?

Because yeah -- if the openings can be limited to once a day, then this would be much less of a problem.

Yes, say you cross Chelsea Creek with a movable bridge where the deck is usually 60' AMSL and raises to 175' for openings. For most vessels the LRT bridge would remain fixed and the Chelsea Street bridge would open, except for the tallest ones where the tankers need the full clearance. Sort of like how the Lechmere Viaduct crosses over anything that needs the other bridges to open (and how I assume it used to work when it was a functional movable bridge). As the fact sheet says, most of the tugs pass before the bridge has even reached its full height. As you can see in these photos I saw on UHub/Mastodon the other day, the tugs are substantially shorter than the tankers. I have no idea about the barges, and I admit that I know very little about maritime stuff in general.

I'm not sure how tall 1A is around the Neptune Road crossing, but if you're already elevated there might be clearance to snake over it even though it's right at the 33L centerline.

Note that the fact sheet was from 2019. I found this rule from March 2020 that says:

"The bridge owner, Massachusetts Department of Transportation (MassDOT), submitted a request to allow the bridge to open to 139 feet above mean high water instead of the full open position of 175 feet unless a full bridge opening is requested."
"This change in opening height reduces the opening time by 2–6 minutes per opening. The Chelsea Street Bridge will perform a full bridge opening of 175 feet above mean high water when requested to do so."

So perhaps 139 ft is the benchmark for balancing the frequency of bridge openings? On one hand, that's still much higher than the 60' that @737900er suggested. On the other hand, at least it's less insane than 175'.

(A 4% grade for a 139' bridge requires 3475' lead, which would start right to the east of Broadway. A 7% grade requires 1986', which starts at Marlborough St.)

Another factor is that a 139' transit bridge can hopefully be opened for a shorter duration of time than the road (i.e. it can keep running until the road rises to 139'), further limiting the disruption to transit, hopefully to an extent that it fits into the headways.

 

[Riverside]

And as @JeffDowntown seemingly implied, the cost of such a tunnel may also be used for a more direct Sullivan-Day Square (or Maverick) connection via Charlestown, which brings more benefits to riders doing OL-Airport, GLX-Airport etc, and is equally capable of being extended to Central Parking or Logan Terminals.

One fun note to consider here (especially in the spirit of Crazy Transit Pitches): Maverick is like... 6? blocks from Loganland.

Specifically the Car Rental (served by 3 Massport shuttle routes).

There are also three empty plots between Bremen and the East Boston Greenway, two of which are publicly owned:

It doesn't get you all the way to the airport... but it gets you most of the way. So if you wanted to connect a Logan APM to Maverick, it might not be as hard as you'd think.

 

[Riverside]

139 feet above mean high water

This probably means it would actually be less than 139 feet above street level, right? Probably not by much, but looks like maybe 5-10 feet? (I still don't think it changes any of the calculus meaningfully though.)

 

[Teban54]

This probably means it would actually be less than 139 feet above street level, right? Probably not by much, but looks like maybe 5-10 feet? (I still don't think it changes any of the calculus meaningfully though.)

I'm not sure about the accuracy of Google Earth Pro at measuring altitudes in such an urban setup (though it does seem to give very fine-grained results), but here's what I get for altitudes along Grand Junction ROW:

• Immediately to the north of the bridge: 10 ft
• Eastern Ave/Central Ave junction: 2 ft
• Cottage St: 5 ft
• Bellingham St: 6-7 ft
• Marlborough St: 7-8 ft
• Box District station: 5 ft

So you're probably looking at 131-134 ft above street level, which isn't much of a difference. (Using 132', the 4% and 7% lead lengths change to 3300' and 1886', down from 3475' and 1986', respectively. Pretty negligible.)

 

[ritchiew]

In a real Urban Ring future world, wouldn't you take the same approach for the Mystic crossing, and end up with a Sullivan Under station?

Yeah, maybe, depending what you mean for the Urban Ring. The BRT proposals and some types of train proposals would just use existing road/train bridges, and that could be fine. For most UR-rail proposals, I think, there would need to be a new, dedicated crossing of the Mystic, and you're right, immersed tube tunnel might be the way to do that.

But also, a new Mystic crossing could be a simple bridge. The specific problem with the Chelsea Creek bridge is is has to accommodate large ships underneath, but a new Mystic crossing near Sullivan wouldn't have that requirement. So a new Mystic bridge wouldn't have to be a drawbridge or 150' high or whatever. Generally a bridge is cheaper than a tunnel, but that also depends on how easy it is to connect to whatever approaches from either side of the river. For that, I have no idea in this case.

 

[Riverside]

^ F-Line sketched out an idea that would reuse existing infrastructure for the Mystic. I’ll try to find those later.

 

[Charlie_mta]

Of course, we could take a detour and have an urban ring LRV route that circumvents Chelsea Creek altogether:

 

[Riverside]

Of course, we could take a detour and have an urban ring LRV route that circumvents Chelsea Creek altogether:

View attachment 46399

I could see it maybe working for Chelsea <> Airport service, but wouldn't such a long diversion exacerbate the Sullivan <> Airport travel time problem discussed above?

 

[Teban54]

Of course, we could take a detour and have an urban ring LRV route that circumvents Chelsea Creek altogether:

View attachment 46399

I agree with @Riverside that this is likely a suboptimal solution. More importantly, though, I think we need to go back to the question of what's the problem that we're trying to address regarding a "grade-separated" Chelsea Creek crossing.

Tunnel proposals:

• Is a tunnel so expensive that it's automatically out of question?
• How does the cost depend on the construction method? For example, is an immersed tube tunnel feasible here (assuming it's less expensive than a bored tunnel)?

Bridge proposals:

• Where do the problems with a bridge come from? Is it:
  • Engineering (a bridge that's tall enough may not even be feasible to fit in here in the first place)?
  • Cost (it may still be too expensive to be worth the benefits)?
  • Politics (the bridge and its inclines may be too disruptive to nearby neighborhoods)?
  • Practicality (an Eastern Ave station that's 175' tall may undermine its usefulness)?
  • Or other factors (e.g. Logan may not approve a permanent transit bridge with 175' clearance, despite them seemingly having approved the existing bridge that's 225' tall with 175' clearance)?
• What should the vertical clearance be (60', 139' or 175')?
  • How to balance the height (cost savings, neighborhood impacts) with the number of bridge openings (unreliability)?
• What are we designing the bridge for? This determines the grades needed, which in turns impacts cost and nearby impacts (perhaps even feasibility).
  • LRT only? That means 6-7% grade, but the steepness will have operational impacts (like Science Park-North Station).
  • HRT (or LRT with possible future HRT conversion)? That likely means 5-5.5% grade.
  • Mixed transit/road bridge? That likely means 4% grade.

Demands and benefits:

• What's the mode of transit that we're designing this crossing for? LRT, BRT (may include T104), or APM? Or a mix of them?
• Which route(s) run on this crossing? Does it end at Day Square, or closer to the terminals (Central Parking or Logan Terminals), or across the harbor to Seaport etc? On the opposite end, does it end at Chelsea, or through-run to Sullivan and beyond, or take other directions out of Chelsea (e.g. to Malden)?
• Who are the riders using the crossing, and what are they using it for? Are they Chelsea (and Everett) riders heading closer to downtown - either transferring to BL, heading to the terminals, or continuing to Seaport and downtown? Or are they regional demands with air travelers (and elsewhere on the BL) from Assembly/Sullivan and further west? How many people with such demands do we expect to take this service vs. other alternatives? (Or, perhaps, are they connecting from LRT that ends at Eastern Ave to an APM that ends in the same vicinity?)
• A distinction that's often overlooked: Are we serving air travelers or airport employees?
  • As this blogpost says: "1000 airport employees using an airport service every day are more ridership than 100,000 air travelers using it, on average, maybe a couple of times a year."
• The above questions all lead to this: Are there enough riders using this service, to make the cost of the crossing (in whatever form) worth the benefits?

Last but definitely not least: What's the budget that you're considering or expect to have? (This not only determines the infrastructure, but also the benefits you need to achieve. In some cases, the benefit may be limited enough that the existing bridge may be OK.)

There are various combinations of answers. Different people will have different opinions, and it may be impossible to know the ground truth for each question. But I think the questions themselves are important to keep in mind.