@article{Lupal2017signals,
author={Lupal, N..},
title={Signals and interlocking development during imperialism (1906-1917). Part 4: Safety devices},
journal={Transport automation research},
publisher={FSBEI HE "Emperor Alexander I St. Petersburg State Transport University"},
year={2017},
pages={625-635},
volume={3},
issue={4},
}