This work is a report on research concerning transit service characteristics as seen from the users’ point of view. Users of two separate bus lines, operating in a shared/ common urban infrastructure, were interviewed at bus stops about their perception concerning headways of bus lines operation. An analysis was made regarding deviations between actual and scheduled bus arrival headway. Further statistical analysis was carried out to check factors giving rise to different perceptions. The operation of each bus line was registered, and corresponding service characteristics were compared with those perceived by the users. Based on these results, a model for bus line headways was proposed, incorporating the perception of deviations by the users. In conclusion, a reliable service, meaning smaller deviations, is more appreciated by the public than any service of shorter headways and less reliability.