In Boston MA the local transit authority (MBTA) will leave the diesel busses running all night when the forecast is for cold weather.
I do not know at what temperature they decide to do this.
It is not every winter night.
Bill here in MA we can still run studded tires from November until the end of April.
They do a real number on the road when some one spins a studded tire in one spot.
I used to drive a Zamboni and the studded tires on that would rip up concrete.
[This message has been edited by iwire (edited 11-26-2003).]