A 18-wheeler hauling liquid nitrogen and several other vehicles were involved in a wreck this morning.  Shreveport Police Sgt. Bill Goodin tells KEEL News that the big rig was stopping at the railroad tracks, as it's required to do, at E. Bert Kouns near the Automall.  The car behind it decided to make a quick lane-change, and hit another car, sending it crashing into the rig, knocking the 18-wheeler on its side.  Two people were taken to Willis-Knighton with non-life-threatening injuries.  No evacuations were ordered as a result of the chemical spill, but some parts of that area have to be shut down so equipment can be brought out to put the rig back up on its wheels.  Expect major delays until that's all cleared up.  Stay tuned in to 710 KEEL for updates.