A connected vehicle train-vehicle collision detection system comprises a roadside unit (RSU) located at a railroad grade crossing near a roadway lane for avoiding TRAIN crashes with Onboard Unit (OBU)-equipped vehicles by issuing advance warnings for a potential vehicle-train crash. The roadside unit (RSU) is configured to act as a proxy Onboard Unit (OBU) for a non-OBU-equipped TRAIN and transmit a train location to a first Onboard Unit (OBU)-equipped vehicle having an Onboard Unit (OBU). The Onboard Unit (OBU) of the first OBU-equipped vehicle is configured to calculate a train-vehicle crash based on the train location of the TRAIN relative to the railroad grade crossing and a vehicle location of the first OBU-equipped vehicle relative to the railroad grade crossing.