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

secondary roads, the register could not be used to assess the crash rate on the Yaoundé-Douala section. However, the register made it possible to estimate the completeness of policereports retrieved and digitized. This exercise was only possible in the eight largest policestations and was not conducted in the remaining five smaller ones. All reports from all 13police stations were however included in this study.Data extractionScanned reports were coded, using a grid adapted from the standardized French datasurveillance system [9], and were recorded using EPIINFO 2000 [74]. Crash details includedhour, day, month, and year of crash, number of vehicles and road users involved, situationalfactors such as light and weather conditions, horizontal and vertical road profile, road andshoulder surface conditions, and whether situated in urban zones, at intersection, or near aschool. Involved vehicles were categorized as trucks, personal, utilitarian, and passengervehicles. Involved road users were classified by vehicle type or as pedestrians, bicyclists, andmotorcycle riders. Outcome of these road-users were graded by the police as: not injured,slightly injured, seriously injured (when needing hospital admission), and died. Road userrelatedvariables such as age, sex, profession, means of transport to hospital, and road usercategory (driver, passenger and pedestrian) were recorded when available. For motorizedvehicle users, information on the use of helmet or seat belt and Driving While Intoxicated(DWI) was recorded. Similarly, for pedestrian, information on crossing facilities wasrecorded.In addition, all reports were independently read by two investigators (Emmanuel Lagarde andJöelle Sobngwi-Tambekou), and coded using a standardized grid for crash type, and one ortwo possible causes. No inconsistencies were found for crash type, and when two differentcauses were identified by the two investigators, both were recorded. On some occasions, thecrash corresponded to several types (for example, a two-wheel motorized vehicle versus apedestrian). Such crash type was therefore coded as the type involving the user of highestvulnerability. The vulnerability decreasing order was: one or more pedestrians involved; oneor more two-wheel motorized vehicles; vehicles travelling in opposite directions; singlevehicle running off the road; vehicles travelling in the same direction; one or more still ormanoeuvring vehicle; crash at an intersection).AnalysisCrash and injury risks per 100 million kilometres travelled were computed, with numeratorsbeing numbers of persons or events in the study period, and denominators estimated numberof kilometres travelled on the Yaoundé-Douala road section during the study period [73].These rates were corrected taking into account our estimates of police report completeness, ascompared with the events listed in main police registers. To assess the respective involvementof personal, utility, passenger vehicles and trucks, we divided the number of vehicles of eachtype involved in non-fatal and fatal crashes by kilometres travelled by same vehicle type.Crash and injury risks for specific vehicle and road user group were compared using rateratios and their 95% confidence intervals. Injury severity for different road user groups wasassessed by fatality ratio, fatalities per total injured. Percentage increases in traffic fatalitiesand injuries were computed for the year 2006 compared to 2004. Furthermore, proportions ofcrash causes and situational factors were computed according to crash types. Crash fatalityratios and fatality per crash were compared for crash types and causes. Lastly, the outcome ofinjuries was compared according to road user characteristics. Data were analyzed using SASversion 9.1.3 [75].23