The number of utilities already underground can make it impossible to use an excavator to dig a trench. It can't be dug by hand because there's no way to shore up the sides of the trench to prevent cave-ins. What's a contractor to do? Vacuum the dirt out, that's what! The vertical pipe seen here is attached to a powerful vacuum mounted on a truck.

Here are two of the large vacuum or "vactor" trucks working at the intersection of 4th Avenue and 36th street.