a guy got a ticket for running a red light. he argued in court that the Doppler Shift made the light appear green.
the judge agreed with him that the original ticked was no good, and then fined him... for speeding :)


Lambda(red) = 620nm
Lambda(green) = 520nm
f = c / L
f(red) = 4.84*10^14Hz
f(green) = 5.77*10^14Hz

Assuming that he observed the light over a distance of 50m, there are this many waves of light in the red spectrum:

50 / (620*10^-9) = 8.0645*10^7

In order to "greenshift" that, he needs to cause this many waves to incident his retina:

50 / 520*10^-9) = 9.615*10^7

So he needs to travel at a speed such that he only views 8.0645/9.615 oscillations he otherwise would if he were stationary.

The redshift formula is:

f(final) = f(emit) + f(emit) * v/c

So:
f(final) = 5.77*10^14Hz
f(emit) = 4.84*10^14Hz
c = 3*10^8m/s

v = c * ( ( f(f) - f(e) ) / f(e) )
= 3*10^8*((5.77*10^14 - 4.84*10^14)/4.84*10^14)
= 5.76*10^7m/s

= 207,520,611 km/h

That's one HELL of a speeding ticket.