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- Bagdadi, Omar
(författare)
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The development of methods for detection and assessment of safety critical events in car driving
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Improving our knowledge of drivers’ behaviour, especially in hazardous situations is a key to understanding why accidents occur and how to improve safety on our roads. Crash surrogate measures have proven to be very useful in traffic safety analysis. As a valid crash surrogate measure shares the same logical chain of events as actual crashes, studying those events increases the opportunities to analyze external circumstances as well as events and driver behaviour preceding the crash. A new definition of crash surrogate measures is proposed, i.e. safety critical braking events: Situations (including crashes) that require a sudden, evasive manoeuvre to avoid a crash or to correct for unsafe acts performed by the driver himself/herself or by other road users. This thesis develops a method for detecting Safety CRItical Braking Events (SCRIBE) and evaluates against other methods mostly used in large naturalistic driving studies. The evaluation shows promising results in the success rates of detecting safety critical events. Further, a Method for estimating the SEverity of safety Critical events (M-SEC) involving more than one road user, is developed and evaluated. The method combines a measure of closeness-to-collision, or safety margins, with a measure of possible consequences based on the speed and mass of the involved road users. Besides, a comparison is made with the Traffic Conflict Technique. Evaluation of the method shows that the estimated severity using M-SEC enables comparison of safety critical events involving different types of road users and is not limited to comparisons between similar types of events. In addition, the estimations when using M-SEC seem to reflect the seriousness of the safety critical events.
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| 2. |
- Varhelyi, Andras
(författare)
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Dynamic speed adaptation based on information technology - a theoretical background
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Knowledge on the factors influencing driver speed-behaviour, the relationship between speed and traffic safety and means to influence speed behaviour is systematised. Expert judgements and the high proportion of injury accidents show that improved speed adaptation has the largest safety potential in the following situations: - Road surface-, visibility and weather affected situations (e.g. slippery road, fog, darkness). - Places where sudden speed reduction is needed (e.g. motorway exits, sharp bends). - Encounters with crossing-course both between motor vehicles and between motor vehicles and pedestrians/bicyclists (e.g. at intersections, at zebra crossings). A study on driver speed behaviour in encounters with pedestrians at a zebra crossing shows that in such situations there is a need for better speed adaptation. In an encounter with a pedestrian, the driver has to be influenced before he reaches the "decision zone" at 50 to 40 m before the zebra crossing, in order to prevent the "signalling by speed" behaviour. A nationwide survey among 1000 holders of Swedish driving licences shows that the majority of the respondents are positive to a device which automatically lowers the maximum possible speed of the car in slippery conditions and poor visibility, as well as to a device which warns the driver or reduces the speed automatically if the car is about to collide with another road-user. A general system which prevents exceeding the prevailing speed limit is accepted by one third. A system, which limits the maximal speed of the vehicle in the actual situation via an in-vehicle equipment is proposed. A system algorithm to calculate the appropriate highest speed in different conditions is presented. The estimated safety effect of the proposed system, if all cars are equipped, is a 20% - 40% reduction of injury accidents reported to the police.
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