Mississippi, I was pleasantly amazed to discover, used an amazing variety of bridge designs in the early years of the Interstate system. 'I-20 in Mississippi kept me thoroughly entertained," I said after my first trip through. I'm gonna catalog the early designs along I-20, west to east- - not every bridge, but every type. The other Interstates, maybe another day.
Most states had gotten away from concrete T beams by 1971, but four of
these gracefully arched structures carry I-20 and its ramps just east of the 1973 Mississippi River bridge. A bit to the east, three of
these long-span plate girder bridges, also from 1971, are used at the I-20-US 61 interchange. All of these bridges now have Jersey barrier parapets, which were likely not original equipment.
These 1960 plate girder structures with open concrete guardrails supported by an intricate deck edge cantilever carry I-20 over eastbound old US 80. A few hundred feet east,
these concrete box beams with a much cleaner open concrete guardrail design carry it over westbound old US 80. And another few hundred feet away,
this plate girder design with the cleaner open concrete guardrail carries a ramp.
At the next interchange, with the northern leg of US 61,
these 1961 precast beam bridges with open concrete guardrail carry the US 61 mainline. A few hundred feet east,
this curving cast-in-place concrete box beam caries a ramp. The previous box beam I mentioned was supported on a bent, but this one's round columns extend directly into and are integrated with the box beam. Except for the guardrail, it's quite California-looking.
Moving east, the next bridge over I-20 is
another bent-supported concrete box beam, but here the open concrete guardrail is topped by a single-tube metal rail to make it a bit less harrowing for any pedestrians who venture out upon it. It's fair to call this bent-supported box beam with open concrete guardrails a standard design of its era.
Since we're here, I must mention a pair of real unicorns: these two
1955 plate girder bridges with old skool picket-type guardrail with two horizintal concrete lintels. It's amazing that these bridges still survive when so many newer ones in nearby Vicksburg have been replaced with boring, modern AASHTO beam structures.
Starting at mile 25 or so are
these 1971 Californian cast-in-place concrete box beams, supported by single columns integrated with the beams and with a painfully short single-tube metal guardrail. Also from 1971,
these precast beam bridges with spindly-looking bents carry the I-20 mainline. This one still has the original, very short concrete parapet, though its companion is having its parapet replaced by something more modern.
Others have more substantial-looking bent columns.
Just west of Jackson are
these 1969 cast-in-place box beams. Unlike the ones I've mentioned previously, the edge cantilevers are very short, IMO making them less attractive that the others I've listed.
The guardrail on these looks similar to a Jersey barrier, but not identical. I can't say that this is a standard design, but I wouldn't be surprised to find it elsewhere in the state.
This precast beam design definitely qualifies as standard, being used for most of the bridges carrying the mainline. This one's guardrail is the same short, solid concrete design we've already seen on mainline bridges, but topped here by a single-tube metal rail. A whole bunch of these were built in 1966, including for the interchange with the southern leg of I-55. This design comes in plate girder, too, including
this steel straddle bent monster carrying the eastbound I-20 mainline over I-55.
Damn, this is a lot of work, and probably no one will read it. Ima skip ahead to east of Meridian, where we find
the quintessential Mississippi early Interstate bridge design, c. 1961. It's a cast-in-place T beam with integrated columns and, I think, a slightly different open concrete guardrail. I'd say that this is the equal of any other state's quirky early Interstate bridge design.
Also, there's
this 1960 box beam design on T-shaped columns isolated from the beams rather than integrated. I'm a sucker for T-shaped columns.
Wow, I can call myself finished now! Here's one more, though:
this one is a 1966 single-column cast-in-place box beam over the highway, but with short precast spans over the adjacent creek.
