Traffic accident problem is a critical public-health concern in Thailand. Despite a number of prevention measures launched in the past, with the country’s growing economy and population expansion, the incidence of traffic accidents in Thailand still remains on the rise. This research therefore sought to assess the relationship between traffic accident incidences sorted by causes and provincial economic status well as its dynamicity over time. This study used multiple cross-sectional research design. Data were obtained from an annual national survey by between 2006 and 2015 and. The dataset is composed of (1) traffic accident incidence in each province between 2006 and 2015, retrieved from the National Statistical Office, and (2) gross provincial product (GPP) per capita obtained from the National Economic and Social Development Board. Concentration index (CI) was used as a proxy that represents a size of inequity of traffic-accident incidences. It is clear that the incidence (per 1 00 000 people) nationwide gradually increased, from 63.8 in 2006 to 91.1 in 2015. Human causes accounted for over half of the total accidents. The CI estimates of all-causes accidents continuously declined from 0.139 in 2006 to 0.076 and 0.057 in 2010 and 2012 respectively, but after 2013, the CI estimates took negative values (−0.035 in 2014 and −0.051 in 2015). This reflected that, in recent years, traffic accidents in Thailand tended to be more concentrated amongst less well-off provinces (pro-poor), obviously contrast to the situation before 2013. However a statistical significance of CI was observed only before 2010. The contribution of this study to a wider policy implication is using CI as means to prioritize the urgency and intensity of accident prevention measures. Less well-off provinces should be the main target of the policies at present, and the measures should be deliberately designed to fit the varying context of each province.