The regulations determine the minimum length of passing sight distance as the function of design speed. Researches have confirmed that passing sight distance has a positive impact on capacity for relatively low traffic volume. Recent researches show that the definition of passing capabilities as percentage of zones with forbidden passing (no passing zone) does not describe sufficiently well the real state. In this paper are presented the results of the research on the section of the main road (Vr = 80 km/h), which show that the minimum lengths of passing zones (passing sight distances) have very little effect evan at very low traffic flow rate. The basic parameter of the capacity analysis is PTSF (percent time spent following). By increasing the length of the passing distances, the positive impact increases significantly to a certain limit (optimum length). A further increase loses meaning (does not give a significant effect). The obtained results indicate that additional research could provide design guidance on optimum lengths of passing zone as the function of speed and traffic flow rate.

passing sight distance, optimal length, capacity analyses, PTSF