DISASTER: Wreck of the Red Arrow

Under normal circumstances, the engineman of the Pennsylvania Railroad's flyer Red Arrow has a clear track as his train roars through Philadelphia's famed Main Line suburbs on its run from Detroit. But as it came hurtling in toward the city at 7:30 one morning last week, complications developed up ahead; the Philadelphia-bound Pittsburgh Night Express—which was running 48 minutes late on the same track—had been stopped up ahead by a block signal near the station at Bryn Mawr.

Other signals began flashing a warning (repeated by colored lights in the cab of...