Traffic Safety Potential and Effectiveness of Lane Keeping Support
Doctoral thesis, 2020
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 four papers providing knowledge of lane keeping support integrated in vehicles and road infrastructure. More precise, the safety potential and effectiveness of Lane Departure Warning (LDW) was studied as well as the effectiveness of centreline rumble strips (CLRS). Also, the potential safety benefits of Emergency Lane Keeping (ELK) and Autonomous Emergency Steering (AES) with enhanced lateral vehicle positioning were studied. Reviewing real-world in-depth data of 138 fatal crashes in Sweden 2010 and 114 in 2017, the results show that virtually half of the single vehicle and head-on crashes involved unintentional drift-out-of-lane, where LDW, ELK and AES should have had the potential to prevent the majority of these crashes. Estimating the effectiveness of LDW by analysing 1,853 police reported real-world injury crashes during 2007‒2015 extracted from the Swedish Traffic Accident Data Acquisition (STRADA) database and applying the induced exposure method, it was found that LDW halved the risk of being in a head-on or single passenger car injury crash. Posted speed limits were at 70 km/h and above and the road surface had not been covered by ice or snow. Estimating the effectiveness of CLRS by merging STRADA injury crashes during 2011‒2016 involving 7,490 cars with the National Road Database in Sweden (NVDB) and applying the induced exposure method, the results show a reduction in head-on and single car crashes. Crashes involving drift-out-of-lane to the left were reduced by 40% (19‒56%) for ESC-equipped cars, and by 29% (11‒44%) for cars without ESC. It could be confirmed that in-depth data with high detail can provide benefits in evaluating future road safety features. Furthermore, it was found that merging STRADA, NVDB and individual vehicle equipment data has significant methodological benefits in combination with data efficient methods such as the induced exposure approach.
LDW provided by the vehicle industry and detectable lane markings provided by road authorities are parts of a system showing significant traffic safety benefits. As both components are dependent on each other, this makes safety the responsibility of both road authorities and the vehicle industry. Not only do LDW and CLRS complement each other, they also complement ESC and are able to avoid critical situations. LDW and CLRS are two of the most important traffic safety features for the foreseeable future, in which the share of unintentional lane drifting crashes is expected to increase. ELK will in the near future be mandatory for new cars, hereby detectable lanes and lateral vehicle position awareness will be even more important. Future research should focus on increasing the synergy between car and infrastructure interventions, holistically and systematically utilising the integrated safety chain.