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

MethodsStudy design and settingsThe study settings were interurban road sections situated in Cameroon and Pakistan:1/ Karachi-Hala road section in Pakistan (196-km-long mostly four-lane separated road), and2/ Yaoundé-Douala road section in Cameroon (243-km-long mostly two-lane non-separatedroad). 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 was obtainedfrom the Aga Khan University Ethics Research Committee in May 2009 (ReferenceERC/2009/1179).Site selectionIn Pakistan, NHMP regional office was visited in the month of June 2009. Crash reports andregisters for the three-year period from Jan 1, 2006 to Dec 12, 2008 were retrieved andphotocopied. High-risk sites with given kilometre location were then identified with GPScoordinates with help of a police officer. Similarly, traffic police offices in Cameroon werevisited and such sites were subsequently identified in June 2007. The two road sections werefilmed from a four-wheeled sedan car moving within the authorized speed limit (July 2009 inPakistan and July 2007 in Cameroon). All high- and low-risk sites were then identified bylinking GPS coordinates to the videos. For each high-risk site, a low-risk site was randomlyselected out of all sites which were not involved in crashes on the same road section.Video setsTo measure hazard perception, video of sites were cut so that each video showed a 500 metrelong-roadsection during 30 seconds, including the last 100 m corresponding to the high- orlow-risk site (Figure 14). Further, a yellow indicator blinked five times to help drivers identifythe site for which they had to emit a judgement on hazard perception right after videoprojection. We determined sample size to be 26 pairs of sites, assuming that 95% of the highrisksites would be identified as dangerous and 80% of the low-risk sites as not dangerouswith a precision of 7.5 [125].Participant selectionParticipants were Pakistani nationals residing in Karachi, aged 18 years or more, with a validdriving permit, who had driven a motorized vehicle on the Karachi-Hala road section in theprevious seven days. Random sampling was not possible because of heavy-traffic and higherspeeds conditions on this road section [30]. Thus, a convenience, but representative, samplingmethod was used to recruit 100 drivers. For this, we determined the drivers’ sex and vehiculardistribution by observing traffic from a pilot study (N=5 496). It was observed that carsaccounted for 39.1%, heavy trucks for 36.5%, minibuses and mini-trucks for 7.8%, buses for9.6%, and motorcycles for 6.3% of the vehicles entering Karachi (Appendix 8). Distributionof cars and heavy vehicles was similar to that recorded by highway authority [83]. Almost alldrivers were men (99.9%). Based on these findings, personal vehicle male drivers wereinvited from a roadside gas station at start of the highway near Karachi, and commercialvehicle drivers were invited from transport company offices at six different locations inKarachi.Data collectionFace-to-face interviews with drivers were conducted in Urdu language. Questions weredeveloped from an English language questionnaire, using back translation, independentlinguistic verification, and testing on five drivers. Interviews were either conducted at the Aga48