The increasing demands for high data rates necessitate the development of faster schemes of exchanging information along wireless communication links. Physical-Layer Network Coding (PNC) is a promising technique that can improve the achievable data flow rates through higher packet transmission rates, thereby increasing the overall throughput. In this paper, we study the performance of the PNC transmission technique in unidirectional linear flow networks, and compare it with that of the traditional transmission technique. We first derive the bit-error rate (BER) that the PNC transmission scheme achieves, and then using that, we evaluate the end-to-end flow throughput of unidirectional flows. Our results show that PNC has a great potential for enhancing the achievable throughput, especially under medium to high signal-to-noise ratios. We also validate the derived BER results using simulations.