The passage way of road vehicles, humans and domestic animals over rails is called “crossing” at railways. The most significant of crossing are roadway crossings and level crossings have particular importance among them. Railway level crossings safety influences on rail and road transportation safety. 10% of rail accidents occur on crossings and 10% of crossing accidents cause to death. This issue indicates the importance of crossing safety. Several factors is effective in crossing safety. For example, rail and road vehicles should be aware of approaching the crossing at a proper distance and have appropriate visibility to each other for safe passage through crossings. So line and road sight obstacles should be eliminated at specified distance. In this paper, we try to determine proper dimensions of unobstructed area for maximum speed 120 km/hr of passenger trains and maximum road speed limit 120 km/hr of Iran railway lines by examining previous studies in other countries, Iran railway regulations and international standards. Railway track and road should not have horizontal or vertical arc at this distance and to provide enough visibility, any obstacles including trees, buildings, fixed or mobile equipments and etc. should not exist in distances forming triangle. Also the effects should be considered if there is any slope in both sides of crossing at railway track, road or any speeds change in calculations.
