Scientists had plenty of opportunity to study impacts of 30km/h given the vast amount of data – it has been implemented in many countries for decades and has been trialed in small areas in Australia already.
There is vast amount of research from around the world that proves that 30km/h is the better speed for neighbourhood areas.
The City of Yarra, Melbourne put together research and background on their 30km/h trial:
NSW Centre for Road Safety has published statistics on stopping distances & survival probabilities at different speeds
Safe speed: promoting safe walking and cycling by reducing traffic speed by Dr. Jan Garrard
Prof. Danny Dorling: If You Could Do One Thing: Nine Local Actions to Reduce Health Inequalities.
Safe-Street Neighbourhoods: the role of lower speed limits by Dick van den Dool , Paul Tranter and Adrian Boss is a study for Australia that specifically analyses 30km/h speed limit on Australian streets.
In 2019 the Welsh Government said that 20mph should be the default speed limit for residential areas. The Task Force Group set up to “identify the practical actions needed to implement this change” has now reported.
Report that analyses signs only 20mph speed limits. One reason for this interest is the ability to address a far larger area through speed limits only than through traffic calmed zones as implementation is considerable cheaper.
NICE guidelines – speed humps might increase acceleration- and braking-related emissions.
Speed Reduction Study by the German Environment Agency
Effects of city-wide 20 mph (30km/hour) speed limits on road injuries in Bristol, UK where the 20 mph speed limit intervention was associated with a city-level reduction of fatal injuries of around 63%
Lessons on how to get people cycling from the Netherlands, Germany, and Denmark: The key to achieving high levels of cycling appears to be the provision of separate cycling facilities along heavily traveled roads and at intersections, combined with slow traffic of most residential neighborhoods