Speed Trap - RC one not 1:1..

[Balders]

Have a few events coming up where we thought a speed trap at the end of the straight might be a fun addition.

Basically am after a fixed trap that displays MPH of passing car on a board as they pass.

Am looking for something like this but on a larger scale that can measure the track width:

http://www.ebay.co.uk/itm/GOLF-SWING...item51abf65663

Anyone used or tried something like this before?

Cheers

Mike