What I've done here was to run three videos simultaneously, compare the R, G and B values separately and take the highest or lowest value for each of the pixels.
And the results were... so scary, the cars really looked like ghosts!
Ghosts(1) from kynd on Vimeo.
Ghosts(2) from kynd on Vimeo.
Ghosts(3) from kynd on Vimeo.