30kph residential speed limit improves safety with little effect on travel times

Reducing residential speed limits from 50 kilometres per hour to 30kph would significantly boost bicycle riding safety without majorly affecting car trip times, a study has found.

The findings come as the Australian state of Victoria enacts a new speed limit law allowing local councils to propose 30kph limits in school zones and local streets.

Modelling by RMIT University’s Centre for Urban Research showed bicycle riders’ exposure to roads with high levels of traffic stress dropped by 30% when the speed limit was reduced from 50kph to 30kph.

Researchers rated every road in the Australian Greater Melbourne region for traffic stress levels using a framework that considers factors like speed limits, cycling infrastructure and traffic volume, based on government survey data and travel modelling.

They found lowering residential speed limits to 30kph more than doubled the proportion of an average bicycle trip on low stress streets and roads from just over one-third to more than two-thirds.

Study lead author Dr Afshin Jafari said while driving at 30kph might seem slow, the limit mostly applies to residential streets, so it has little impact on average car trips, while the modelling showed the average short local trip only increased by about one minute.

“Most trips should use residential streets only at the start and finish, so 30kph rather than 50kph on those short sections makes little difference,” he said.

“Slowing traffic makes bicycle riding less stressful, encouraging more people to choose bikes as a safe and viable mode of transport.”

Jafari said lowering speed limits was a practical, low-cost way to improve cycling safety.

“Installing physical barriers on every local street would be ideal, but it’s expensive and slow,” he said.

“Slowing down vehicles is a cheap and effective way to improve safety while we wait for longer-term infrastructure upgrades.”

The 30kph residential limits would also encourage motorists to use main roads, leading to quieter residential streets.

“This should also create safer streets for our kids,” Jafari said.

While bicycle riding is often seen as the domain of city commuters, Jafari said outer city suburbs stood to benefit the most from lower speed limits.

“Outer suburban streets often don’t even have footpaths, let alone other infrastructure to separate bicycle riders and pedestrians from motorists,” he said.

‘Modelling the impact of lower speed limits on residential streets for cyclist level of traffic stress and car travel time in Greater Melbourne’, is published in the Journal of Cycling and Micromobility Research. DOI: 10.1016/j.jcmr.2025.100085