thèse doctorat de l'université bordeaux 2 - ISPED-Enseignement à ...

oad). A matched strategy was used to select sites. ‘High-risk sites’ were those involved inthree or more RTCs in a precedent three-year period, whereas ‘low-risk sites’ were those notinvolved in a RTC, during the same period. For each high-risk site, a low-risk site wasrandomly selected on the same road section. Hazard perception was assessed by showingvideos of these sites to voluntary Pakistani drivers. Ethical approval of the study design wasobtained from the Aga Khan University (AKU) Ethics Research Committee in May 2009(Reference ERC/2009/1179).Site selectionIn Pakistan, National Highway & Motorway Police (NHMP) regional office wasvisited in June 2009. Crash reports and registers for the three-year period from Jan 1, 2006 toDec 12, 2008 were retrieved and photocopied. High-risk sites with given kilometer locationwere then identified with Global Positioning System (GPS) coordinates with help of a policeofficer. Similarly, traffic police offices in Cameroon were visited and such sites weresubsequently identified in June 2007 (Bhatti, Sobngwi-Tambekou, Lagarde, & Salmi). Thetwo road sections were filmed from a four-wheeled sedan car moving within the authorizedspeed limit (July 2009 in Pakistan and July 2007 in Cameroon). All high- and low-risk siteswere then identified by linking GPS coordinates to the videos. For each high-risk site, a lowrisksite was randomly selected out of all sites on the same road section which were notinvolved in crashes.Video setsTo measure hazard perception, video of sites were cut so that each video showed a500-meter-long road section during 30 seconds, including the last 100 m corresponding to thehigh- or low-risk site. Further, a yellow indicator blinked five times to help drivers identifythe site for which they had to emit a judgment on hazard perception during video projection.We determined sample size to be 26 pairs of sites, assuming that 95% of the high-risk siteswould be identified as dangerous and 80% of the low-risk sites as not dangerous with aprecision of 7.5 (Flahault, Cadilhac, & Thomas, 2005).Participant selectionParticipants were Pakistani nationals residing in Karachi, aged 18 years or more, witha valid driving permit, who had driven a motorized vehicle on the Karachi-Hala road sectionin the previous seven days. Random sampling was not possible because of heavy-traffic andhigher speed conditions on this road section (Hijar, Carrillo, Flores, Anaya, & Lopez, 2000).Thus, a convenience, but representative, sampling method was used to recruit 100 drivers. Forthis, we determined the drivers’ sex and vehicular distribution by observing traffic from apilot study (N=5 496). It was observed that cars accounted for 39.1%, heavy trucks for 36.5%,minibuses and mini-trucks for 7.8%, buses for 9.6%, and motorcycles for 6.3% of the vehiclesentering Karachi. Distribution of cars and heavy vehicles was similar to that recorded byhighway authority (NHA, 2008). Almost all drivers were men (99.9%). Based on thesefindings, personal vehicle male drivers were invited from a roadside gas station at start of thehighway near Karachi, and commercial vehicle drivers were invited from transport companyoffices at six different locations in Karachi.Data collectionFace-to-face interviews with drivers were conducted in Urdu language. These weredeveloped from an English language questionnaire using back translation, independentlinguistic verification, and testing on five drivers. Interviews were either conducted at the AgaKhan University (AKU) Campus or at the company offices in separate rooms. Driver-related126