  In this paper, we document a design, implementation, and field tests of a
vehicle-to-vehicle (V2V) communication-enabled rail collision avoidance system
(RCAS) for urban light rail vehicles---trams. The RCAS runs onboard a tram and
issues an acoustic warning to a tram driver if a collision with another tram is
imminent---no commands to the braking subsystem are issued in the current
version. The prediction of an imminent collision with another tram is based on
real-time evaluation of predicted trajectories of both trams. The predictions
are based on mathematical models of the longitudinal dynamics of the vehicles
and real-time estimation of the current motion states (position and velocity).
The information about the other tram's predicted trajectory is accessed through
V2V communication. We also document the results of verification of the
functionality of the proposed RCAS through several field tests with a real
tram.

Systems and Control;Systems and Control