When drivers are attempting to make a turn across the path of oncoming traffic, they often must determine whether it is safe to initiate a turn (e.g., when turning at an unsignalized intersection).  This requires drivers to scan the roadway for oncoming vehicles and to judge whether there is sufficient time for them to complete the turn before an oncoming vehicle arrives. In the field of human factors, a driver’s judgment of whether there is a sufficient gap in traffic to complete a maneuver is referred to as gap judgment.  A driver’s willingness to accept a particular size gap (e.g., distance of an oncoming vehicle from the intersection) is referred to as gap acceptance.

In motor vehicle crashes involving a turning vehicle, human factors experts evaluate the reasonableness of a driver’s decision to turn across oncoming traffic by comparing their actions to what other drivers are likely to do under similar circumstances.  This includes analyzing the turning driver’s ability to accurately judge the gap and their decision to accept a particular size gap under the circumstances.