New Jersey State Route 129 is a short north-south highway in Trenton. It goes from Lamberton Road to U.S. Rt. 1. NJ St Rt 129 passes through the following town in Mercer County. Trenton NJ St Rt 129 is not multi-plexed in Mercer County. NJ St Rt 129 intersects the following highways in Mercer County. New Jersey State Route 29, at Trenton. U.S. Rt. 206, at Trenton. U.S. Rt. 1, at Treton.