811 locate marks are ±24 inches but gas lines are 12 inches wide

When an excavator calls 811 before digging, the utility locator marks the approximate position of buried gas lines with paint or flags. But the industry-accepted accuracy tolerance is ±24 inches from the actual line — meaning the mark could be up to 4 feet off. Gas distribution mains are often only 4-12 inches in diameter. So the painted mark on the ground creates a false sense of safety: a contractor sees the mark, digs 18 inches away thinking they're clear, and strikes a line that was actually right under their shovel. This mismatch between marking precision and pipe size is the single biggest reason the U.S. still sees 400,000-800,000 underground utility strikes per year despite the 811 system existing since 2005. Each strike averages $4,000 in direct costs but $116,000 when you include indirect costs (project delays, emergency response, legal liability) at a 29:1 ratio. The tolerance persists because improving it would require switching from electromagnetic locating (which reads the field around a pipe, not the pipe itself) to higher-precision methods like GPR or vacuum excavation, which cost 5-10x more per locate. No one wants to pay for it — not the utilities, not the one-call centers, not the excavators — so the ±24-inch fiction continues and 167,000 strikes happen per year even when 811 was called.