The Safety Potential and Effectiveness of Lane Departure Warning Systems in Passenger Cars

Abstract: In the road transport system, crashes due to lane departure account for a large proportion of the most severe crashes that passenger car occupants are exposed to. While Electronic Stability Control (ESC) effectively prevents lane departure due to loss of control, lane departure due to unintentional drifting has not been addressed to the same extent. This thesis is based on two papers aimed at increasing the knowledge of the safety potential and effectiveness of lane keeping support. Paper 1 aims to identify and characterise lane departure crashes and identify the safety potential of lateral support systems such as Lane Departure Warning (LDW) by using real-world in-depth data of fatal crashes in Sweden. Single car, head-on and overtaking crashes involving lane departure without prior loss of control were categorised into intentional lane change, evasive manoeuvre or unintentional drift out of lane. The latter category accounted for half (51/100) of the single vehicle and head-on crashes and LDW systems have the potential to prevent a majority (33 to 38) of these crashes.  Paper 2 aims to estimate the effectiveness of LDW in real-world passenger car injury crashes, extracted from the Swedish Traffic Accident Data Acquisition (STRADA). The induced exposure method and information of each individual car’s equipment were used. LDW halved the risk of being in a head-on or single passenger car driver injury crash where the posted speed limits were 70 km/h and above and where the road surface was not covered by ice or snow. This thesis shows results in line with other research considering the safety potential and effectiveness of lane keeping support. While related research used risk measure exposure such as insured vehicle days or vehicle miles travelled to estimate effectiveness of LDW, Paper 2 used induced exposure where the exposure is made up by non-sensitive crashes. The induced exposure method has advantages of incorporating possible changes in driver behaviour and usage rates in real-world traffic. Despite applying two very different methods of analysis, the two papers synthesised in this thesis show results that corroborate each other. In conclusion, LDW is part of a system where detectable lane markings provided by road authorities and vehicles technology have to work together and shows significant traffic safety benefits under certain conditions. As both components are dependent on each other to create safety, this makes safety the responsibility of both road authorities and the car industry. Lane keeping support systems, such as LDW, is one of the most important safety features in the foreseeable future, where the share of unintentional drifting crashes could be expected to increase due to ESC addressing loss of control. Therefore, different organisations and road safety stakeholders should promote the fitment of LDW systems in new cars and speed up the implementation in traffic.