Note: The famous Erie Triplex, the Matt H. Shay, is often said to have proved unsuccessful because the firebox grate area was not large enough to provide adequate steam for three sets of drivers, and the rear engine lost adhesion as the coal and water supply above it was used up. Some authorities, however, have pointed out that the locomotive was intended for low-speed helper service over short distances, a task which involved coasting back downgrade and resting idle for long periods of time. For this type of service, the firebox and steam supply were adequate enough.