CTA subway has no ballast can attest as far back as 1980 start of career.
Have worked single tracks above ground and under as flagman many years ago when the track workers replace rail and or switches etc soon as they are done a signal maintainer would be on site for speed to go back to normal.
In block signal territory when done the slow zone signs are taken down to resume normal operation.
Job of flagman was to protect the workers and stop the oncoming trains but have seen motorman as they were called then called operators when conductors were eliminated run pass hit the track trip throwing train in emergency
Then they would be disciplined , if flagman was in error he also would face consequences.
Retired Switchman ATU Local 308
