The load of trash is huge. Curbs are a foot high because of the seasonally heavy rainfall. By morning, the gutters are filled to sidewalk level. However, it takes only a few hours to get the streets cleaned for the next night's debauch. They even have almost all the drunks off the street by dawn.
N.O. does not wait until Mardi Gras is over to clean up. Celebrations go on for at least four days and the tourists want clean streets every night to throw up in.