DULUTH, MN (KDAL) - A convoy of logging trucks passed through downtown Duluth Thursday morning as drivers are protesting new federal load limits.  At least 50 trucks were involved as members of the Associated Contract Loggers and Truckers of Minnesota rolled down London Road and Superior Street to Garfield Avenue.  The new weight limits would reduce the size of loads to 80 thousand pounds on the Interstate system.  Logging trucks normally carry 90 thousand pounds or more and say the limit will cause a hazard since they will have to use city streets instead of the freeway.