This documents what George said about the lights being distance guides to the vehicle ahead.

In a close column movement, vehicles are spread approximately 25 meters apart during daylight conditions. At night, vehicles are spaced so that the driver can see two lights in the blackout marker of the vehicle ahead. Close column is normally used for movements during darkness, under blackout driving conditions. This method of movement takes maximum advantage of the traffic capacity of the route used, but provides very little dispersion of vehicles.

http://www.tpub.com/content/armychem...m3300b0043.htm