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An experimental study of the brake-application time of Autonomous Emergency Braking (AEB) system considering the primary accident in an urban area was proposed. Since the functionality of the brake-application time is varied between manufacturers and models, the brake-application time of AEB system must be verified based on driving behaviour in Malaysia. A primary accident was simulated to acquire vehicle deceleration rate in real condition by driving an ego vehicle at a different set of vehicle speeds. The study is focussed on the urban roads in the north region of West Malaysia, i.e. Penang. As a benchmark in this study, the brake-application time (2.6 s) introduced by Mercedes-Benz in the PRE-SAFE® Brakes technology was referred. A new braking permission time was proposed by calculating a minimum deceleration distance and Time-to-Collison (TTC) confirmation time required to brake based on maximum deceleration when a primary accident was simulated. It was found that the brake-application time recommended for the AEB system, specifically AEB City conveys the real driving condition of Penang when a primary accident happens in the urban area. To have a smooth braking and an optimum braking performance during a primary accident, the Forward Collision Warning (FCW) should be activated at TTC ≤ 4.6 s. The partial braking (PB) should be activated automatically when the TTC is approximately 2.9 s. While the automated full braking (FB) phase should begin when the TTC reaches 1.1 s.

This study uses a simulation of primary accident to investigate the scene barrier effects on vehicle deceleration rate in the suburban area to assess driver behaviour. Several conditions were designed and experimented to determine the capability of scene barrier, which included free flow traffic without an accident, an accident without scene barrier and an accident with scene barrier. The vehicle deceleration rate was investigated by collecting speed-time data in normal traffic zone and rubbernecking zone. Results found that the average vehicle deceleration rate reached as high as - 1.93 km/h/s in rubbernecking zone compared to normal traffic zone (as high as - 0.49 km/h/s) especially when an accident was simulated without the scene barrier. Introduction of scene barrier during the simulated accident improved traffic flow and reduced rubbernecking phenomena by improving the average vehicle deceleration rate in rubbernecking zone by up to 43.0 %. However, sudden deceleration cannot be totally eliminated during the simulated accident with the scene barrier due to driver behaviour. For optimization of braking time during a primary accident, a study of the algorithm of Autonomous Emergency Braking (AEB) system is necessary.

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