This review evaluates the effectiveness of city-wide 30 km/h speed limits in Europe, focusing on safety, environment, energy, traffic, and livability. The study analyzed data from 40 European cities, including Brussels, Paris, and Zurich, showing that 30 km/h speed limits reduced road crashes by 23%, fatalities by 37%, and injuries by 38%. Lower speeds also improved environmental outcomes, with emissions decreasing by 18%, noise pollution by 2.5 dB, and fuel consumption by 7%. These reductions contributed to safer, more sustainable urban environments. The study also found that 30 km/h speed limits encouraged walking, cycling, and public transit use, enhancing urban livability. Cities like Brussels, Paris, and Zurich reported significant decreases in road crashes, injuries, and fatalities after implementing 30 km/h limits. Additionally, noise and air pollution levels decreased, with traffic noise dropping by up to 3 dB and nitrogen dioxide emissions decreasing by up to 29%. While some studies suggested that lower speeds might increase emissions under constant-speed conditions, the overall impact of 30 km/h limits on energy efficiency and environmental sustainability was positive. The study concludes that city-wide 30 km/h speed limits are an effective strategy for improving road safety, reducing environmental impact, and promoting sustainable urban development.This review evaluates the effectiveness of city-wide 30 km/h speed limits in Europe, focusing on safety, environment, energy, traffic, and livability. The study analyzed data from 40 European cities, including Brussels, Paris, and Zurich, showing that 30 km/h speed limits reduced road crashes by 23%, fatalities by 37%, and injuries by 38%. Lower speeds also improved environmental outcomes, with emissions decreasing by 18%, noise pollution by 2.5 dB, and fuel consumption by 7%. These reductions contributed to safer, more sustainable urban environments. The study also found that 30 km/h speed limits encouraged walking, cycling, and public transit use, enhancing urban livability. Cities like Brussels, Paris, and Zurich reported significant decreases in road crashes, injuries, and fatalities after implementing 30 km/h limits. Additionally, noise and air pollution levels decreased, with traffic noise dropping by up to 3 dB and nitrogen dioxide emissions decreasing by up to 29%. While some studies suggested that lower speeds might increase emissions under constant-speed conditions, the overall impact of 30 km/h limits on energy efficiency and environmental sustainability was positive. The study concludes that city-wide 30 km/h speed limits are an effective strategy for improving road safety, reducing environmental impact, and promoting sustainable urban development.