In this paper, we describe a dynamic train-to-train (T2T) millimeter wave (mmWave) propagation measurement campaign to enable the automatic train coupling application. mmWave frontends with directive antennas were installed on the couplers of two trains where the channel impulse response was recorded throughout the measurements. The campaign covered more than 30 recorded measurements in different environments. Received signal power in the open field area was analyzed and modeled using a two-ray pathloss model. Results indicate that the received power next to a platform was higher compared to the open field counterpart due to strong contributions from the signals reflected by the platform. Distance estimation accuracy between the transmitter and the receiver using a snapshot based estimator was evaluated and 1sigma accuracy of 12 cm was achieved.