A left-turning vehicle (Subject Vehicle, SV) attempting to cross the path of an oncoming vehicle (Principal Other Vehicle, POV) at an intersection typically does not have the right of way. The main task of the SV driver is to find an adequate opportunity in opposing traffic to initiate the left-turn maneuver. To reduce the probability of a conflict, warning systems, such as Intersection Decision Support (IDS) systems, are being developed. These systems alert drivers of SV vehicles attempting to negotiate a left turnabout traffic approaching from the opposite direction. The current paper (i) describes a video system that was used to assess gap length, gap acceptance and gap rejection in a Left Turn Across Path/Opposite Direction(LTAP-OD) scenario, (ii) describes a way to characterize gap distribution (log-normal) presented to the SV driver, and (iii) illustrates how a logistic model often used to describe dose- response curves can be used to characterize gap acceptance by the SV driver. These results are used as the basis for a discussion of implications for IDS systems for alerting left-turning drivers about oncoming vehicles.