Speeding is a major risk factors for road traffic injuries in Bangkok. The objective was to understand speeding prevalence, and examine associated factors in Bangkok, Thailand. Five rounds of cross-sectional data were collected between July 2015–September 2017 using standardized protocols. Observation locations were selected through systematic sampling. Speed was measured using a microwave radar gun on weekdays/weekends, and five times during each day. The speeding prevalence was calculated based on established speed-limits in Bangkok. Descriptive analysis estimated city-wide, and area/road specific-speed prevalence. Regression analysis examined key factors associated with speeding. Over 700 000 vehicles were observed across the five rounds. The speeding prevalence ranged from 32%–47% across the five rounds. Speeding was common during weekdays (round 1:67%; round 2:69%; round 3:70%; round 4:75% and round 5:61%) and during evenings (21% in rounds 1–3 and 22% in rounds 4–5). Larger vehicles were more likely to speed. Speeding was more likely on arterial roads (round 1:84%; round 2:79%; round 3:81%; round 4:74% and round 5:86%) as compared to collector roads. Overall, 46% of speeding vehicles were at ≤10 km/hour above the posted speed limit while 30% were between 11–20 km/hour. Multivariate regression analysis revealed that minibuses were nine times more likely to speed than motorcycles (aOR: 9.20), and commercial vehicles were 16% less likely to speed compared to private vehicles. Our results highlight the increased susceptibility of motorcyclists and other vulnerable road users due to larger speeding vehicles on the roads in Bangkok. Speeding was also highest during weekends and evenings. Considering the limited resources, these findings could be invaluable to design more efficient and targeted road safety programs including but not limited to appropriate messaging and data-led enforcement of legislation. Such an approach would be key to reducing the burden of road traffic injuries in cities like Bangkok.