What factor is crucial in determining the gap needed for a safe left-hand turn?

The speed of oncoming traffic is a crucial factor in determining the gap needed for a safe left-hand turn because it directly affects how much time a driver has to complete the turn without endangering themselves or other road users. When oncoming traffic is traveling at high speeds, a larger gap is needed to ensure that the turn can be made safely. This requires the driver to judge not only the distance of the oncoming vehicles but also their speed, allowing for enough time to make the turn before they reach the intersection.

Other factors, such as the time of day, may influence visibility and traffic conditions, but they do not directly dictate the gap required for a safe maneuver. Similarly, while the color of traffic signals is essential for understanding right-of-way rules, it does not provide guidance on safe turning gaps in the context of oncoming traffic. The type of vehicle making the turn can have some influence, as larger vehicles may require more space, but it is the speed of those approaching that ultimately dictates how much space is necessary to ensure safety.