I crossed both of those bridges (in a car) several years ago. They are 10 ft lanes. I was following a semi that had a trailer that wasn't tracking straight. Trailer wheels were scrubbing the curb and the tractor wheels were nearly on the white line. I *think* they have finally banned trucks on those two bridges.
i try to find different ways to cross the Big Muddy just to say I did.
You didn't say which way you are headed or what type of vehicle. Heading East,If you cross on I-57 get off at Cairo Junction, exit 1 and go a block or so over to OLD US 51 (AKA Ohio River Scenic Byway or S Vienna Rd), now Illinois 37 and follow it until you turn right on Illinois 169 and follow it till you turn right on US 45 and continue to Metropolis. This is a scenic and enjoyable ride and is good road all the way. Stop in Metropolis at the courthouse and say Hi to Superman.
Be aware that many of the river crossings on the Mississippi and the Missouri are still closed, including the new bridge at Cape Girardeau.
Charles
'03 Ram 2500 CTD, 5.9HO six speed, PacBrake Exh Brake, std cab, long bed, Leer top and 2008 Bigfoot 25B21RB.. previously (both gone) 2008 Thor/Dutchman Freedom Spirit 180 & 2007 Winnebago View 23H Motorhome.