See: Wired News:
The December CGA report — the first comprehensive look at digging accidents — found that nearly half of the 675,000 incidents in 2004 resulted from the excavator failing to contact the local One Call center. The most common facilities damaged as a result were gas pipelines, representing 51.6 percent of the damage. Telecommunications facilities came in second at 27.5 percent. Backhoes, trenchers and shovels tended to hit gas lines, while augers, borers and drills had it in for telecom cables.