Abstract: At approximately 5:45 a.m. on July 8, 1992, a runaway muck train consisting of two muck cars and one flat car was in the Johns Hopkins inbound tunnel. Employees #1, #2, #3, #4, and #5 were working from a high car (a car with scaffolding used to hang plastic sheets of waterproofing). The runaway train hit the high car and all five employees were knocked from the scaffolding. Employees #1 through #5 were sent to the hospital, where all but one were treated and released. Employee #2 remained hospitalized. The three loaded muck cars had been secured by only one chain. As a locomotive passed, the chain broke, causing the muck cars to run away. The employer is strictly enforcing that rule that parked cars be both chained and blocked. To further prevent a similar accident, present air brake systems are being converted to have automatic parking brakes when the air hoses are disconnected.