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Chesapeake Bay Bridge-Tunnel

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Mapmikey:
AADT on the CBBT north of the pier was 8800 for 2015...

For comparison, US 301's AADT at the Virginia end of the Nice Bridge is 26000, although that segment goes all the way back to VA 206 so not all of this is traffic merging onto the bridge (AADT at VA 3 is 14000, so the true number is somewhere in between).  I know there are backups sometimes on 301 at this merge.

I don't know what the lifespan of a tunnel like these is supposed to be but the original tunnels will be nearing 60 years old when this parallel tunnel is opened, so having a new tunnel in place is an ok idea even if traffic and safety weren't issues...

cpzilliacus:

--- Quote from: Mapmikey on November 22, 2016, 12:32:43 PM ---I don't know what the lifespan of a tunnel like these is supposed to be but the original tunnels will be nearing 60 years old when this parallel tunnel is opened, so having a new tunnel in place is an ok idea even if traffic and safety weren't issues...
--- End quote ---

When the Fort McHenry Tunnel (I-95) in Baltimore opened to traffic in 1985, one of Baltimore Harbor Tunnel  (I-895) tubes was immediately closed for total reconstruction, followed by the other tube. Both tubes needed it badly as the traffic there was pretty heavy from the time it opened in 1957, and the state could never do a long-term closure.

There is a similar dynamic at the CBBT.  When the overwater trestled roadways were twinned, all traffic was moved to the new structures so significant work could be done on the "old" (now usually northbound) trestles (not sure how long that took, as I did not cross it during that work).

Once the new Thimble Shoal Tunnel is open, the existing Thimble Shoal tube can be shut-down for thorough rehabilitation and repair work.  Presumably at some point in the future, the CBBTD will twin the  Chesapeake Channel Tunnel (north tube) as well, so that existing tube can also receive the rehabilitation and repair work that it needs.

cpzilliacus:

--- Quote from: Mapmikey link=topic=19225.msg2188277#msg2188277 ---For comparison, US 301's AADT at the Virginia end of the Nice Bridge is 26000, although that segment goes all the way back to VA 206 so not all of this is traffic merging onto the bridge (AADT at VA 3 is 14000, so the true number is somewhere in between).  I know there are backups sometimes on 301 at this merge.

--- End quote ---

According to the 2015 State Highway Administration's Highway Location Reference, AADT on the crossing  itself is 18,576.

Even though that part of 301 is toll (MDTA) maintenance, SHA still publishes the traffic volumes for it, as they do for all MDTA-maintained roads in the state.

froggie:
Part of it is safety-driven, which was the primary reason for the twinning of the bridge portions.  Another part of it is condition...the Thimble Shoals portals have had some cracking.  Lastly, parameters have changed from the previous plan for a parallel Thimble Shoals tunnel to a brand new 4-lane tunnel there because of a desire from the Navy for a deeper Thimble Shoals channel.  The current tunnel plan would support a deeper channel.

Regarding bottlenecks at the tunnels....they aren't significant, but in my (extensive) experience, there are two things that can happen that are technically considered bottlenecks:  A) platoons of traffic lining up behind someone driving slow through the tunnels.  I've personally been stuck behind timid drivers who will barely go 30 through the tunnel, and by the time we clear, there's a few dozen vehicles (including trucks) lined up behind the lead vehicle;  B)  incidents, whether a crash, maintenance inside the tunnel, or the need to stop traffic in both directions for an oversize/permit vehicle, can easily stop traffic for a half hour or more.

epzik8:
So does this mean the tunnel portions will no longer be a two-way single bore? There will be two bores with one for each direction?

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