Gap Acceptance and Time-To-Arrival Estimates as Basis for Informal Communication between Pedestrians and Vehicles

Informal communication plays a crucial role for negotiation processes in transport and thus, needs to be implemented in automated vehicles. Slowing down to encourage pedestrians to cross is one example of informal communication. To implement naturally-looking automated slowdown, a first step is to examine expected moments of braking from a pedestrian's perspective. Gap Acceptance and Time-To-Arrival (TTA) estimates can provide these timings. The present experimental study assessed the effects of vehicle size, speed and participant's age on expected braking initiation. Pre-recorded real-world videos of approaching cars (truck/smart) with various speed (10 to 40 km/h) on a parking area were presented to 42 participants from 18 to 75 years. Results showed more risky estimations/decisions with increasing speed. Older participants showed more conservative gap acceptance. Vehicle size only influenced TTA estimations (size-arrival-effect) but not gap acceptance. Thus, applying one simple time gap value does not fit human/pedestrians perception and expectations.