Years ago I was gathering signatures for a petition drive and I personally got over 100 people to sign just from approaching people at bus stops. It was probably one of the most productive places to find people. Two suggestions:

1. When you approach someone, make sure to state right off the bat that your work seeks to improve transit for riders (if indeed that’s true). People who depend on transit have an incentive to go along with the interview if your work will indirectly help the riders that you interview.
2. Downtown has the highest concentration of bus stops and bus riders, so do it there. Don’t camp out at only one stop either, circulate.