There is an ascending, eastbound grade inside the tunnel, which forced locomotives to work harder and produce more smoke and fumes while inside. Ventilation was not required for westbound trains, which could drift downgrade with the throttle closed. For this reason a ventilation plant was only needed at the west portal of the tunnel.
Trains operating through the tunnel had to comply with speed restrictions (limits). Westbound trains 20MPH. Eastbound trains, when fan is running, 10MPH. Fan out of service, 20 MPH.
Note that the railroad allowed a higher speed when the fan was not in use to permit crews to exit the 2500-foot bore as quickly as possible.