Based on crashes in France the mortality risk of pedestrians, when hit by a car was low (about 1%) at an impact speed of 30 km/h, but increased by a factor of 2 at 40 km/h, a factor of 6 at 50 km/h and a factor of 18 at 60 km/h (European Road Safety Observatory, 2021).

In July 2016, the city of Edinburgh lowered the speed limit on almost all of its roads from 30 mph to 20 mph. The city center, main streets, and residential roads all became 20 mph zones. The zones with a reduced speed limit saw 38% decrease in the number of road crashes (371 fewer crashes per year), including fewer crashes involving cyclists and pedestrians (VICE, 2022).

Graz in Austria was the first major European city to adopt a zone of 30 km/h limit, applying to all city areas, in 1992. Nowadays, in this city covering some 127.58 km², 80% of roads are limited to 30 km/h. One of the aims of this measure was to improve air quality and to reduce reliance on cars (City30-brussels). There has been a 12% reduction in the number of road crashed and a 24% decrease in serious injuries (ROSPA,2017).

Brussels is a 30 km/h zone established on 1 January, 2021. Maximum speed is 30 km/h on all roads in the Brussels Capital region, except of the major axes where the speed limit remains 50 or 70 km/h. Five months after installing the general speed limit of 30 km there was an overall 10% decrease in the number of road crashes, while one year later, a 50% reduction in road fatalities was identified (City30-brussels). 

Bilbao in June 2018, began reducing the speed limit to 30 km/h with the triple aim of reducing noise, pollution and increasing road safety. It was named European City of the Year at the 2018 Urbanism Awards and is the first city in the world with more than 300,000 inhabitants to have introduced a 30 limit on all of its streets. Between 2019 and 2020, the city had reduced by 23% the road crashes (Eurocities, 2021). Indeed, the groups that were initially most resistant to the measures (taxi drivers, traders and delivery drivers) are now happy to acknowledge that the lower speed limit does not cause them any problems and in fact improves traffic flow (City30.brussels, 2022).

A study by the French national research institute Cerema found that the number of pedestrians injured or killed in Grenoble had been 50% reduced since the city has set 30 km/h as speed limit (City30-brussels). As for Lille, it is the first city in France (on August 2020) with over 500,000 inhabitants that has lowered its speed limit to 30 km/h almost everywhere gradually. The main benefit after three years is that the number of cyclists had significantly increased by 55% more comparing to 2016 (City30.brussels,2022).

Referring to the capital of France, Paris, since the 30th of August 2021 vehicle traffic has been limited to 30 km/h, except for selected roads such as the Champs Elysées (50km/h) and the main ring road, the Boulevard Périférique (70 km/h) (La vitesse limitée à 30 km/h, 2021). Despite some criticism, officials in the French capital said their decision was in line with a survey that showed 59% of Parisians were in favor of the new speed limit (Paris introduces citywide 30 km/h speed limit, 2021). The implementation of this measure led to a 25% decrease in the number of road crashes and a 40% decrease in those considered serious and fatal (Polis, 2021). 

Areas with 20mph limits, such as the city of Portsmouth and Camden in London had a reduction of 22% and 54% in road crashes accordingly (British and Swiss public back 30km/h limits, 2014). Furthermore, cutting from 50 to 30 kph in Munster, Germany has as result the drop of number of people severely injured in road crashes by 72% (Reducing speed limits, 2021).

The first widespread evaluation of the equivalent 20mph zones in the UK found that injury crashes were reduced by 60%, and child injury crashes were reduced by 67%. In the 20mph zones in Hull, UK, there was a decrease in total crashes of 56% and in fatal and serious injuries of 90%. The largest reductions were pedestrian casualties, which were reduced by 54%, child casualties were reduced by 54% and child pedestrian casualties were reduced by 74% (van den Dool, 2017).

In 2004, Helsinki introduced large-scale 30 km/h restrictions and then the system was extended in 2019. First it was used in the city centre and some residential areas, then speed restrictions were modified in effectively all the streets. After the 2004 change, in the streets with lower speed limits traffic crashes resulting in personal injury decreased by 9 percent. In places where the speed limit was changed from 40 km/h to 30 km/h pedestrian injuries decreased by 19 percent and vehicle damages by 34 percent. The biggest improvement was observed in the city centre, where the number of traffic-related injuries decreased by 42 percent. There is also a recent, 2022 poll concluding that 77 percent of Helsinki citizens feel safe in traffic, and only 5 percent answered that they find transportation in the Finnish capital dangerous (None of the European Cities that lowered the speed limit to 30 km/h regrets it, Arato, 2023).