Road crashes consist a major societal problem worldwide, with 1.19 million road fatalities per year. Speeding is the number one cause of road crashes worldwide, especially in cities where pedestrians, cyclists and motorcyclists are highly exposed and vulnerable in case of a collision. The aim of this paper was to assess the effectiveness of 30 km/h speed limit reduction. Towards that end, a thorough literature review was conducted followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines and the benefits from 30 km/h speed limits in cities were highlighted. This study described the changes in safety, emissions, energy, traffic, liveability and health before and after the implementation of phased city-wide 30 km/h speed limits. Launching public awareness campaigns and encouraging the use of active mobility, could be proved beneficial for the adoption of 30 km/h speed limits in cities.