It's the light of the oncoming train.

The light at the end of the tunnel is just the light of an oncoming train.

The light you see at the end of the tunnel is the front of an oncoming train.

We wish we could tell you there's light at the end of the tunnel, but it's probably an oncoming train.

There were no gates, no lights, no bells, no stop signs to warn of an oncoming train, ... One month before our accident a man was killed there, and one week before our accident there was another accident. In all there were eight people killed in a period of seven years at this one particular crossing before gates and lights were installed.

For I light my candle from their torches.