Which statement best describes the function of closing probability?

• A. It is the distance to the next vehicle
• B. It is the probability of a vehicle changing lanes
• C. It is the chance that two objects move closer together along their projected paths
• D. It is the time to collision estimate

Answer: (C)

Closing probability is about how likely it is that two moving objects will end up closer to each other given their current speeds and directions, taking into account uncertainties in their projected paths. This focus on potential convergence of paths captures risk from relative motion, not just a static gap or a single time estimate. It differs from simply knowing the distance to the next vehicle, which is a present measurement, and from time to collision, which gives a specific moment in time rather than a probability. It also isn’t about whether a vehicle will change lanes, which concerns driver behavior rather than geometric proximity. So the statement describing it as the chance that two objects move closer together along their projected paths best describes the function of closing probability.