First...there isn't a non-terminal CR stop on the system that brings in 300 people per train every train, let alone one in Zone 1A that's in walking distance of the Orange Line and doubled-up by shuttle buses diffusing its demand across several modes.
-- Zone 3 Salem, the busiest northside stop and second-busiest CR stop of all, does 2,058 weekday Blue Book boardings spread across 34 daily inbound trains. That's 60 riders per train projected across the whole service day, though in real terms that's a lot more riders per train at peak and way way way less riders per train off-peak.
-- Providence, the single busiest CR stop of all and largest outlying destination served by commuter rail, does 2,325 weekday Blue Book boardings spread across 20 daily inbound trains. 116 per train, similarly with a monstrous skew towards rush hour slots and away from off-peak slots.
What mechanism exists for packing 150 per train on just 6 trips on a limited and low-frequency weekend off-peak schedule to a single 33-acre parcel in Zone 1A when that target isn't achievable with the whole of Greater Providence on a weekday??? The Wynn-on-Weekends stop not only would have to hit that inexplicable an outlier on target boardings, but sustain the average every single weekend without fail. Including during the winter tourist offseason, bad weather, and weekends there's no special events at the casino. As one street address' worth of attractions in an area that's in literal eyeshot of several hundred other attractions. We're many orders of magnitude beyond calling this place a mere demand outlier now.
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Second...the cost of modifying the bridge grade with backfill is tens of millions in EIS'ing on a navigable river, + design, + construction, + service disruption mitigation. $50M total cost would not be out of the question because this is also touching soil bordering the ex-Monsato property and may need even more intensive environmental remediation if the current embankment is disturbed to the soil base where more nasty stuff is currently capped off. All of that is simply the up-front prerequisite that even allows you a relaxed-enough grade to spend a couple $M more to build the platform at Wynn's front door. Where does the T and Wynn Resorts get an ROI on that extreme a capital-cost prerequisite from Zone 1A receipts after you've downsized that revenue intake with realistic "less than weekday Providence Metro" ridership counts and reduce gross gate receipts to few-to-several $10's of thousands per day instead of $150K?
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Third...this still doesn't counterpoint Wynn's own internal transit investment assessment. Wynn Resorts is outright cutting a check to increase OL off-peak service. On weeknights, not weekends, because that is their self-identified surge period. They're funding local shuttle buses to cover the grid, tap the Logan transfers, leverage Silver Line Gateway and all the Seaport-goers. Because they see those transfer points as their main taps into network-effects demand with the rest of the system. This is real money down. What hasn't gotten real money down, or discussions of possible real money: the Purple Line, and specifically a weekender audience.
It's not enough for one citizen to crunch some numbers and hypothesize that the weekender audience may be so huge once it catches on that a 1A stop could out-average Providence for a full weekend. The only thing that matters is that for-profit Wynn Resorts has already studied its profit-enhancing transit options well enough to quote real dollar figures for money it intends to shell out to the T, and made a business decision to put $x down for bus and subway mode enhancements because it would help their profits and $0 for any CR mode enhancements because it wouldn't help their profits. The case for a CR stop isn't a case of tugging at the state's heartstrings that it's a nice-to-have. It's got to be grounded in profit motive and argued direct to Wynn Resorts, who've been winners at this casinos-n'-resorts game long enough to know who their door-to-door demand is. Wynn made a business decision that this mode matters to their margins because it draws ridership from here, here, and there at W, X, Y times of day on Z frequencies...but that mode from somewhere else during some other time of day at some other frequency doesn't hit the right kind of sweet spot. You have to first convince for-profit Wynn that they're sorely mistaken on their own assessment of the Boston market and give them an empirical case that, yes, "that" mode matters way way more than their internals conclude.
Civil Engineering Strongman Competition of couldas & hypotheticals with the bridge doesn't make that case. Neither do novel farebox recovery formulas that show more people want to ride a Saturday schedule slate there than want to commute from Providence to Boston on a weekday. Whatever it is, Wynn's already crunched those numbers themselves to greater precision than any of us amateur casino-mogul accountants are capable of. And they firmly concluded "that" particular source of ridership isn't what's going to tickle their profits like chasing riders on the other modes they are indeed cutting checks for.