Airport Way between Louise Avenue and Northgate Drive in West Manteca was shut down shortly before 4 p.m. Tuesday after a suspected explosive device was discovered in a black plastic bag at the Union Pacific Railroad tracks.A Union Pacific employee found the bag stuffed into the top of one of several sand-filled safety tubs on the shoulder of the road used to protect the railroad crossing arms and signaling device from errant traffic. He called in his concerns to his dispatcher who alerted law enforcement. That call ultimately brought the San Joaquin County Metropolitan Bomb Squad with officers from the San Joaquin County Sheriff’s Office and the Manteca Police Department.