NH2060 wrote:F-line to Dudley via Park wrote:NH2060 wrote:The existing swing span to be replaced in Spring 2017 (with fair use quote) :
Commuter rail service from Salem to Rockport and Newburyport will be shut down for 21 days as part of a massive, $23 million project to replace the failing railroad bridge between Salem and Beverly.
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Only the swing's deck and motors/hydraulics.
Hence the "swing span" part. It's also a relatively short one at that compared to most other swing bridges.
All things considered though the T probably would have done well to replace it with a bascule span instead to lower the risk of any barge/boat strikes. The width of the "navigable channel" so to speak in between the two sets of approaches is narrow enough before factoring in the center "resting barrier" for the swing bridge. They've happened before and when they do it only makes for a messy commute. Even the Saugus River draw with its own problems AFAIK hasn't had that issue.
Lifts are what provide the widest possible channel. They're also the least maintenance-intensive, most reliable to operate, fastest-moving (because you can adjust the height of the opening to the size of the boat and not need to go 100% every time), and the longest-lasting because the purely vertical motion allows for heavier/sturdier decking and lighter counterweights. They're also popular for retrofits where old approach spans are fully rehabbable but the moving mechanism needs to be cleanroomed with something all-new. Amtrak did a couple of bascule-to-lift conversions on the NEC Shoreline that were 50/50 recycled approaches and all-new centers. It's resulted in much-improved reliability and lifted the ceiling a bit higher on max. train frequencies between openings.
While this is a welcome and long-overdue rehabilitation it's still well short of a permanent solution for Beverly's problems. The approaches are still a patch job on old problematic pilings that'll need refreshing every 20 years unlike the pricier and way more intensive Haverhill/Merrimack rehab that resets the lifespan clock at a "like-new" 50-75 years. It's still a maintenance-intensive old swing design where design itself, regardless of new components, is more liable to get stuck than a bascule or lift. And it's still as narrow a channel as before with very restricted boat speed limit that's going to impose an upper limit on Newburyport/Rockport frequencies (which could be a problem if Portsmouth service is a 25-30 year consideration). And it has just as elevated a risk of bridge strikes as before with that narrow channel and the same old swing mechanism staying in-place.
Saugus River where the boat traffic has declined to trace levels, any replacement for Saugus Draw could/should be a fixed span (and will have to be if that's the reserved routing for the Blue Line Lynn extension traveling side-by-side a la Red + Old Colony over the Neponset). But Beverly probably does have enough taller-mast boat traffic where a movable is going to be needed no matter what and going fixed just isn't feasible or economical. It may even be dense enough boat traffic where it doesn't make a hell of a lot of difference if a replacement movable were any taller than the current bridge. But it definitely would benefit bigtime from doing one of those Amtrak Shoreline-like conversions to a lift center span with double-wide shipping channel. As-is, they're just buying 20 years of state-of-repair before the next rehab, and dealing with the same general design restrictions that make swings of that type really unfavorable to keep using if there's any alternative choice in the matter. There's a reason why commuter and Class I freight RR's alike spend the extra cash for these swing/bascule-to-lift conversions when the option is available. The lowered maint headaches and bridge-strike liability going forward make it well worth their while to get it over with when it's a high-traffic and/or un-bypassable line.