Tiger Transit - Princeton University's transit system is open to the public and it's free.
Princeton Muni Transit
The free Princeton Municipal Bus Service is open to the entire community, the route follows two (2) loops beginning and ending at the Princeton Shopping Center. The northern loop is 31 minutes long and the southern loop is 39 minutes long. The total round trip is 1 hour and 10 minutes.
New Jersey Transit Bus 606 - Travel to work, connect to New Jersey Transit's River Line at the Trenton Transit Center, or visit the Capital City and rediscover the past. All of that and a lot more of Mercer County to be seen on the 606.