Globally, Road traffic injuries (RTIs) account for 1.35 million deaths each year, making them the leading cause of death among young people aged 5-25 years and the 8th leading cause of death among all age groups. Most of these deaths occur in Low- and Middle-Income Countries (LMICs) due to rapid urbanization and motorization amid poor infrastructure and weak emergency response. In these countries, motorcycle riders are most at risk because of their relatively high speed, low crashworthiness and poor occupant protection, and head injury is the leading cause of death and disability. Helmets are an effective and low-cost preventive intervention, but their use remains low in many LMICs like Nigeria where commercial motorcycles are a common mode of transportation. Despite the cost-effectiveness of helmets, country-specific data on patterns of use in Nigeria is lacking making the design and implementation of promotion efforts challenging. This project aims to promote helmet use among commercial motorcycle riders in Nigeria. The objectives were to characterize the prevalence of helmet use, to describe the reasons for non-use and to design an intervention to promote helmet adoption. In four purposively selected, high-traffic locations in Abuja, Nigeria's capital city and a major urban center, video-based observation and surveys of motorcycle riders were used to characterize helmet use. The findings were then contextualized through discussions with stakeholders. The studies confirm a low prevalence of both reported (12.8%, N=755) and observed (0.7%, N=6255) helmet use among motorcycle riders. Most riders are young men (median age 30, N=755). In the surveys, 90% of respondents believe helmets are protective, but the most commonly cited reasons for non-use were lack of enforcement (30%) and physical discomfort (28%) among self-reported non-users (N=658). Among those who use helmets (N=97), personal protection (70.1%) and avoiding penalties (15.5%) were the main reasons cited for use of helmets. Even though helmet use is legally required, the federal agency responsible for enforcement has limited manpower and other competing enforcement priorities. By contrast, motorcycle unions to which riders are compelled to pay union dues appear to exert a greater influence on rider behavior. There are two main implications of these findings. First, traditional approaches to promoting helmet use like government enforcement and rider education, are likely to have limited effectiveness in Nigeria. Second, there is an opportunity to use innovative ways to modify rider behavior by leveraging union influence over riders. This thesis proposes one social innovation, Helmet as an Ad (HeAd) that exploits the market potential of helmets for mobile outdoor advertising to incentivize helmet adoption among commercial riders. Despite the small surface area of the helmet, the high exposure per rider and the synergistic effect of multiple riders make helmets an ideal opportunity for outdoor display of easily recognizable consumer brands. Executed in partnership with the unions, this innovation would generate incremental revenue incentivizing riders to use helmets and unions to informally enforce use.