Background: In Ethiopia, there are an estimated 25.3 road traffic related deaths per 100,000 population, which is much higher than the global average road traffic fatality rate. Speed is the most well-known risk factor influencing both the risk as well as the severity of the resulting injuries. Although there is paucity of data from low-income countries, speed reducers have been widely approved as an effective traffic calming countermeasure in high-income countries. We aimed to (i) explore the effectiveness of transverse vertical speed reducers and, (ii) qualitatively explore stakeholders’ perceptions of the factors that affect the risk of road traffic crashes.Methods: Data on all crashes occurring from September 2010 to August 2015 were obtained. Interrupted time series analysis using Poisson regression was used to estimate the effect of speed reducers on the number of crashes per month before and after their installation in January 2012. Focus group discussions and in-depth interviews were conducted with traffic police, drivers, drivers’ training center owners, and community members to describe their perceptions about the effects of the speed reducers. Quantitative and qualitative results were triangulated.Results: There were 130 crashes during the study period. Of these, 45.4% were property damage only, and 16.9% were fatal. After the speed reducers were installed, there was no statistically significant difference (incidence rate ratio, IRR =1.17, 95% CI[0.60-2.30], p-value =0.644) in the number of crashes per month, but there were changes in the distribution of crash severity (p-value <0.001). Four core themes, with subsequent sub-themes, emerged as perceived contributors to road traffic crashes. Of these core-themes, speedy and reckless driving, were perceived as the strongest force perpetuating road collisions. Qualitative respondents disagreed on whether the speed reducers were effective and expressed concerns such as the lack of signage to warn drivers.Conclusions: Although speed reducers are proven to reduce collisions in high-income settings, this study in Ethiopia was inconclusive. Inappropriate design for the roadway type, sporadic placement, lack of signage and maintenance, and poor stakeholder coordination may have hampered effectiveness. An evidence-based planning process prior to implementing road design interventions is recommended to achieve the desired results.