I had emailed Dollar on this as I was wondering fpor myself... This is their reply:
The Lock Low And Go promotion is as follows:
You lock the rate, we'll pick the ride. Book now at a rate lower
than an Intermediate and we guarantee you an Intermediate size
or larger vehicle. Your vehicle will have room for at least five
passengers and two pieces of luggage. The location will select
the vehicle for you at time of pick-up.
Rates lower than an Intermediate
Intermediate or larger vehicle, guaranteed
Location determines vehicle at time of pick-up.
Vehicle will have at least 5 seatbelts
Room for 2 pieces of luggage or more
Low-mileage, new-model vehicle
A limited number of vehicles are available at this promotional
rate at participating locations through 12/31/07. 24-hour advance
reservations required. Holiday and other blackout periods apply.