Circuir Design for Crossing Blinkers

Can an electricel engineer provide the design an electronic circuit, using photo cells placed between the rails forward and aft of a road crossing, to start and stop the blinking lights at road crossings.
I would like to buy inexpensive electronis parts from Digi-Key etc. to start crossing signal to flash at road crossings as trains approach then stop after the train passes. Can someone provide the circuit design. I purchases five photocells at Radio Shack. The next step is to design the electronics to control the lights.

I am also interested in controling crossing gates. Cananyone help me [:(]

Regards,

Frank Eder

Lots of useful circuits here http://home.cogeco.ca/~rpaisley4/CircuitIndex.html#index

Enjoy!!
Ken.

also check

www.awrr.com
and
www.mrollins.com