Light

Nothing travels faster than the speed of light, with the possible exception of bad news, which obeys its own set of laws.
Light (2), Speed (1), News (3)Douglas Adams (5)

Rowe's Rule: the odds are five to six that the light at the end of the tunnel is the headlight of an oncoming train.
Light (2), Tunnels (1), Trains (1), Traffic (1)Paul Dickson (1)