Speed of light ...
Phoenix Metro Light Rail passing over Tempe Town Lake.
This is the same bridge as the previous shot in my stream, taken from the opposite (east) side; you can just see the old Union Pacific rail bridge in the shadows to its left. Note the colors have changed, as they modify the lighting program after it's formally dark. Up and through dusk they have green and purple lights "run" up and down the bridge, fading in and out. After dark they transition to a rainbow effect (seen here).
Digital blend of 3 different exposures done manually (masks) in CS3: a main exposure, one for the light along the bridge and one for the water.
EXIF: f/11, ISO 400, shutter speeds between 5.0sec (under-bridge lighting) to 25.0sec (main exposure and water)