it's 100sm (straight line) AND 3 hours.
for example - when mdw was opened (before dtw opened) a guy wanted to live in tvc. well within the 100sm but much longer than 3 hours drive time. he had to commute to a point that was within the 3hr limit AND 100 miles.
likewise, around metro new york, you'll be within 100 miles of teb most everywhere, but from way out on long island it'll be more than 3hrs drive, so you'd have to commute to a closer place.
you don't have to physically go to the gateway - you can stay at a cheap place that's 99 miles away.
mapquest is not in the contract, so it can't be used. it's straight line distance.
also, NEVER refuse a briefing (as long as it's a safe briefing). if a screen reader calls and gives you an a/l in an hour, you say "I'LL DO THE BEST I CAN". NEVER REFUSE!!! NEVER tell them it's impossible. "I'LL DO THE BEST I CAN" is the only acceptable repsonse. if you refuse the brief, your a/l will be changed to direct cmh for a disciplinary mtg. If you follow this, and you're within the 100 mile/3hr limits, they can't punish you for missing a flight. you simple call when you arrive and say you missed the flight.
if you're stuck in traffic, a courtesy call is appropriate. also, all driving is based on the legal speed limits in normal traffic.