Background Although motorcycle helmet use has been mandatory in Thailand since the enactment of the helmet law in 1994, the non-compliance in helmet use has been considerably profound. In January 2011, the 100% motorcycle helmet use campaign was launched nationwide, aiming to promote helmet use and reduce road traffic injuries.

Objective The objective of this paper is to investigate whether and to what extent the nationwide helmet use campaign affects helmet use behaviour among motorcyclists.

Methods Effectiveness of the helmet use campaign is evaluated by comparing helmet use rates observed before and after the campaign. Nationwide observational surveys of motorcycle helmet use were conducted in each of 76 provinces in Thailand. Based on stratified sampling methodology, over 3000 locations in urban and rural areas throughout the country were chosen as sentinel sites. In total, 954 956 and 1 236 568 motorcyclists were observed before and after the campaign, respectively.

Results Overall, the motorcycle helmet use rate was found to be slightly higher after the campaign, increasing from 44% to 46%. With respect to seating positions, helmet use among motorcycle riders was virtually unchanged (53% vs 54%). However, we find significant changes in helmet use rates among passengers, increasing from 19% to 24%.

Conclusion Despite the emerging evidence of increased helmet use after the nationwide motorcycle helmet use campaign, the observed helmet use rates remain very low. More importantly, the magnitude of the effect appears to be marginal, compared with the resources allocated. These suggest that the current approaches of promoting helmet use through education and enforcement need to be reviewed and improved.