Validation of in-car observations, a method for driver assessment Magnus Hj€ almdahl * , Andr as V arhelyi Department of Technology and Society, Lund University, Lund, Sweden Received 18 February 2003; received in revised form 18 September 2003; accepted 22 September 2003 Abstract An in-car observation method with human observers in the car was studied to establish whether observers could be trained to observe safety variables and register driverÕs behaviour in a correct and coherent way, and whether the drivers drove in their normal driving style, despite the presence of the observers. The study further discussed the observed variables from a safety perspective. First three observers were trained in the observation method and on-road observations were carried out. Their observations were then compared with a key representing a correct observation. After practising the observation method the observers showed a high correlation with the key. To establish whether the test drivers drove in a normal way during the in-car observations, comparisons of 238 spot-speed measurements were carried out. DriverÕs speeds when driving their own private cars were compared with their speeds during the in-car observations. The analysis showed that the drivers drove in the same way when being observed as they did normally. Most of the variables studied in the in-car observations had a well docu- mented relevance to traffic safety. Overall, in-car observation was shown to be a reliable and valid method to observe driver behaviour, and observed changes provide relevant data on traffic safety. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Driver behaviour; In-car observations; Safety assessment; Method validation 1. Introduction A variety of observational methods are currently being used in order to investigate the possi- bility that the use of advanced driver assistance systems (ADAS) may lead to negative behavioural modifications, see e.g. the negative effect of ABS-brakes indicated by behavioural observations of * Corresponding author. Tel.: +46-46-222-48-24; fax: +46-46-12-32-72. E-mail address: magnus.hjalmdahl@tft.lth.se (M. Hj€ almdahl). 0965-8564/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.tra.2003.09.001 Transportation Research Part A 38 (2004) 127–142 www.elsevier.com/locate/tra