My employer is the City of Everett in WA state. The term "trip reduction" was used by another employer for whom I used to work. I think they meant ways to reduce the number of individual commuting cars on the road. So by biking or carpooling, there would be less car "trips" with single drivers. The City of Everett actually calls their program a "rideshare", even if you are walking or biking. I am not sure how common it is for employers to compensate employees who rideshare. I know I had never heard of it before.