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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.