Here in Erie, PA there is a system in the inner city called Rado-Lite (a 
trade name) which allows police and ambulance vehicles to gain right of 
way by controlling traffic lights through RADIO signals.  The receivers 
look much like what you describe, but they include a UHF whip antenna (less
than a foot tall) and a light which flashes on and off to let traffic know that 
an emergency vehicle has taken control and is approaching.  Local folklore 
says this system was invented here; I don't know if this company has any 
other installations.  It has been in operation for at least 30 years, going 
only by my memory.