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[lordsutch]

Suppose the Memphis-Arkansas bridge were closed.  Could the Hernando Desoto bridge handle all the traffic?

I think the bridge itself could as long as all six lanes are in service (it usually does fine even with a lane closed when they're doing seismic retrofit work). The Tennessee approaches, though, probably would be a bottleneck at rush hour since they narrow to two lanes for a few thousand feet.

[iBallasticwolf2]

Suppose the Memphis-Arkansas bridge were closed.  Could the Hernando Desoto bridge handle all the traffic?

I think the bridge itself could as long as all six lanes are in service (it usually does fine even with a lane closed when they're doing seismic retrofit work). The Tennessee approaches, though, probably would be a bottleneck at rush hour since they narrow to two lanes for a few thousand feet.

Refer to earlier in the thread for a similar discussion about this.

[Wayward Memphian]

Suppose the Memphis-Arkansas bridge were closed.  Could the Hernando Desoto bridge handle all the traffic?

I think the bridge itself could as long as all six lanes are in service (it usually does fine even with a lane closed when they're doing seismic retrofit work). The Tennessee approaches, though, probably would be a bottleneck at rush hour since they narrow to two lanes for a few thousand feet.

All three lanes on each side would look like a Daytona 500 restart at all times just waiting for the Big One it would bottle neck at the I 240 junction and as well at the 1-55/I-40 merge in West Memphis. It's got a massive cluster×!&* written all over it. I know how the ADHT will tell you how the traffic count didn't facilitate a need for 4 lanes on each side through the West Memphis merge but it's crazy. The last few trips home, the I-40 eastbound reduction from two to one lane has been backed up pretty good at the interchange where it meets I-55.

[MikieTimT]

Hopefully some lessons were learned and there's no drama with this one:

Routine Inspection of Interstate 55 Mississippi River Bridge

[US71]

Suppose the Memphis-Arkansas bridge were closed.  Could the Hernando Desoto bridge handle all the traffic?

I think the bridge itself could as long as all six lanes are in service (it usually does fine even with a lane closed when they're doing seismic retrofit work). The Tennessee approaches, though, probably would be a bottleneck at rush hour since they narrow to two lanes for a few thousand feet.

All three lanes on each side would look like a Daytona 500 restart at all times just waiting for the Big One it would bottle neck at the I 240 junction and as well at the 1-55/I-40 merge in West Memphis. It's got a massive cluster×!&* written all over it. I know how the ADHT will tell you how the traffic count didn't facilitate a need for 4 lanes on each side through the West Memphis merge but it's crazy. The last few trips home, the I-40 eastbound reduction from two to one lane has been backed up pretty good at the interchange where it meets I-55.

Sounds like I-49 during Rush Hour.

[bwana39]

There are several points here. This is an old thread and the one about the interchange that would have MADE this needed is on this thread.https://www.aaroads.com/forum/index.php?topic=20377.msg2622992#msg2622992

They have figured out how to do it without closing the bridge. I probably would do it differently than they are, but I am neither P.E. nor in Tennessee

[I-39]

Both the I-55 and I-40 bridges need to be fully replaced with modern structures ASAP. Even with the retrofits, I don’t trust the I-40 bridge at all.

The problem is $$$ and cooperation between AR and TN is non-existent. Thus, I fear another, worse I-35W situation will occur when the New Madrid fault erupts.

[bwana39]

Both the I-55 and I-40 bridges need to be fully replaced with modern structures ASAP. Even with the retrofits, I don’t trust the I-40 bridge at all.

The problem is $$$ and cooperation between AR and TN is non-existent. Thus, I fear another, worse I-35W situation will occur when the New Madrid fault erupts.

There are two points here. First if the New Madrid goes off big enough to knock these bridges down, the infrastructure to get to them will be impassible.  I doubt they are actually the first things that are going to fail.
Second, additional bridges can give redundancy to the grid and in the intermediate, THE EXISTING (OLD) BRIDGES will have several years of life. We have to remember that when the World Series Earthquake hit San Francisco, that the Embarcadero freeway completely failed. There was damage to the Bay Bridge, but not a total collapse.  I feel that unless Memphis is reduced to rubble that would be the outcome with the bridges in Memphis. 
More lives could be lost on the railroad bridges if one of them failed with a passenger train crossing  at Cairo than if both of the highway bridges at Memphis fell into the river.

I will add we really don't have real world experience with cable stayed bridges in earthquakes.

[Rick Powell]

More lives could be lost on the railroad bridges if one of them failed with a passenger train crossing  at Cairo than if both of the highway bridges at Memphis fell into the river.

Since there are 1,440 minutes in a day, and only about 4 minutes of passenger train exposure a day on the Cairo Bridge, the odds seem to be in favor of a train being at the wrong place at the right time. And if the signals are working right, similar odds of a run-off crash into a vacated space where the bridge used to be, especially with the slow approach of trains over the bridge. The odds of dozens of motor vehicles being on the I-40 or I-55 bridges during the "big one" are substantially higher, with less casualties than a passenger train accident but more certainty that there will be some.

[Wayward Memphian]

Some points here as a kid that grew up near directly on top of the fault line. The likely hood of bridge failure rises the north north you are from Memphis.
Draw a line from the St Francis Lake/Marked Tree to Real foot Lake and that is No Man's Land of a big one breaks off.

That is why I favor any single new bridge to run west of West Memphis to Tunica and the current terminus of I-69 there even when map looking tells you to run it between Marion and West Memphis to Fraser/Millington. That also rules out even if a new northern bridge survives the infrastructure connecting to it is still at greater risk. It is the longer way but the southern crossing provides a way to loop around Greater Memphis.

That is also why Helena as a 4 lane bridge appeals to me. That acts another fail safe to even a new bridge in Memphis failing. I much prefer they push down the I-69 crossing to Lake Village and they build one or both of those I mention

If a big one hits the I-155 Bridge is toast.

[wriddle082]

The I-55 Mississippi River bridge will be closed this weekend, from Friday 10/6 at 8PM to Monday 10/9 at 6AM:

https://www.tn.gov/tdot/news/2023/10/2/i-55-mississippi-river-bridge-closure.html

[ilpt4u]

The I-55 Mississippi River bridge will be closed this weekend, from Friday 10/6 at 8PM to Monday 10/9 at 6AM:

https://www.tn.gov/tdot/news/2023/10/2/i-55-mississippi-river-bridge-closure.html

TDOT uses the I-69 shield on the detour route map. Is Tennessee signing 69 in Memphis now, or are they planning to soon?

[Henry]

The I-55 Mississippi River bridge will be closed this weekend, from Friday 10/6 at 8PM to Monday 10/9 at 6AM:

https://www.tn.gov/tdot/news/2023/10/2/i-55-mississippi-river-bridge-closure.html

TDOT uses the I-69 shield on the detour route map. Is Tennessee signing 69 in Memphis now, or are they planning to soon?

AFAIK, I-69 is not signed anywhere in Memphis. In fact, it's still signed as I-55 and I-240.

[ilpt4u]

Just interesting how TDOT is advertising the detour route…

[wriddle082]

Just interesting how TDOT is advertising the detour route…

Good catch!  I didn’t bother to notice that!

[roadman65]

The I-55 Mississippi River bridge will be closed this weekend, from Friday 10/6 at 8PM to Monday 10/9 at 6AM:

https://www.tn.gov/tdot/news/2023/10/2/i-55-mississippi-river-bridge-closure.html

TDOT uses the I-69 shield on the detour route map. Is Tennessee signing 69 in Memphis now, or are they planning to soon?

AFAIK, I-69 is not signed anywhere in Memphis. In fact, it's still signed as I-55 and I-240.

Yeah just like Virginia don’t sign I-74 like NC does is the same here. MS signs I-69 and once over the line it is dropped.

It could be signed in lieu of the western part of I-240, but then you would have at TN 300 a change in number. If Tennessee even built I-69 up US 51 to Future I-269, it could be done.  However there is no chance of us ever seeing I-69 built between Tenaha, TX and Dyersburg, TN in even our grandkids life. I-55 will be for a long time the north way out on freeway to Memphis with I-155 being the connector to I-69 to Canada.

[bwana39]

Oh come on, It (I-69) MAY reach Haughton LA......

[abqtraveler]

Oh come on, It (I-69) MAY reach Haughton LA......

The southeastern bypass of Sherveport/Bossier (I-49S to I-20E) I think has a better chance of being built than any other section of I-69 between Memphis and Tenaha, save for the stretch in Arkansas that's being built out to 2 lanes between Monticello and McGehee.

[bwana39]

Oh come on, It (I-69) MAY reach Haughton LA......

The southeastern bypass of Shreveport/Bossier (I-49S to I-20E) I think has a better chance of being built than any other section of I-69 between Memphis and Tenaha, save for the stretch in Arkansas that's being built out to 2 lanes between Monticello and McGehee.

They would probably build the rest of it into Texas if the entire Shreveport / Bossier part gets built.  It will probably only be around 14 miles from the state line to I-49. I agree fully with you on the I-49 to I-20 part being the only part with any urgency. The I-49 to the Port is almost set in stone. It looks like there MAY be a toll bridge built too. SO I-49 to US-71. The rest of it?????

[The Ghostbuster]

I could see Louisiana eventually building Interstate 69 in their state between Interstate 20 and Interstate 49, and possibly to connect with Texas's segment of Interstate 69. Beyond Interstate 20 seems less likely to me. Even then, I don't expect Interstate 69 within Louisiana to be built in any shape or form anytime soon.

[MikeTheActuary]

AFAIK, I-69 is not signed anywhere in Memphis. In fact, it's still signed as I-55 and I-240.

When I asked TDOT about that several years ago, I was told that from TDOT's official perspective, they don't consider I-69 to exist in Memphis. They weren't planning to make it official until that stretch of future I-69 connected up to a not-yet-constructed standalone stretch of I-69, and that it wouldn't be official until signs were posted, the installation inspected, and an announcement made.

(Months later they failed to ever make that public announcement for the changeover of part of TN 385 to I-269.)