This paper presents a methodology to assess the effect of the length of passing zone on the operation and safety of two-lane rural highways based on the probability and the rate of passing maneuvers ending in a no-passing zone. The methodology was applied using observed passing maneuver data collected with tripod-mounted camcorders at passing zones in Uganda. Findings show that the rate at which passing maneuvers end in a no-passing zone increases with traffic volume and unequal distribution of traffic in the two directions, absolute vertical grade, and percent of heavy vehicles in the subject direction. Additionally, the probability of passing maneuvers ending in a no-passing zone reaches 0.50 when the remaining sight distance from the beginning of the passing zone is 245. m for passenger cars or short trucks (2-3 axles), and 300. m for long trucks (4-7 axles) as the passed vehicles. These results suggest policy changes in design and marking of passing zones to enhance safety and operation of two-lane rural highways.