Imagine a world without speed limits. For some drivers it might sound like freedom, but speed limits play a vital role in keeping road users safe.
Words: Jeremy Rochow
Speed limits are a surprisingly polarising topic. Only recently, the Adelaide City Council caused uproar after floating the idea to reduce city speed limits to 30km/h in the CBD and North Adelaide. While some pedestrian groups supported the idea, other people labelled the idea “ridiculous”, “confusing” and even “extreme”.
It’s not an isolated case either. In 2017, the State Government announced it was going to reduce the speed limit on eight regional roads from 110km/h to 100km/h. Despite the speed limit being altered due to the roads’ bad crash histories, many locals were still outraged. People complained the lower speed limit would increase travel times, which could increase driver risk due to fatigue.
Setting speed limits isn’t as straightforward as just choosing a number though – there are a lot of factors to consider. So, do you want to know how a speed limit for a particular road is chosen or why some councils have 40km/h speed limits in residential streets?
If you feel the need – the need for speed (limits), strap yourself in as we delve into this important road safety tool.
Speed limits save lives
According to a University of Adelaide study, the risk of being involved in a casualty crash is twice as great at 65km/h as it is at 60km/h, and four times greater at 70km/h.
Several studies have shown how speed and the likelihood of crashing are linked. Research published in the Accident Analysis and Prevention journal in 2013 demonstrated that lower speed limits reduce the likelihood of casualty crashes.
RAA Senior Manager of Safety and Infrastructure Charles Mountain says a simple reduction in speed from 60km/h to 50km/h can reduce a vehicle’s stopping distance by 30 per cent.
“That’s as far as 10 metres,” Charles says.
“This fact has influenced the decision to review, and where appropriate, change many speed limits.
“General limit reviews happen regularly, often resulting in speed limits changing to try and reduce the number of deaths and injuries on the road.”
Military Road, Tennyson.
Setting the speed limit
While some people might think a number is plucked out of thin air when a speed limit is set, it’s more complicated than that. In South Australia, the Minister for Transport can set speed limits, with some powers given to the Department for Infrastructure and Transport (DIT) and local governments.
When the State Government sets a speed limit, it must reflect the road safety risk and follow rules outlined in the official Speed Limit Guideline for South Australia, while also keeping traffic flowing.
Charles says before setting a speed limit or changing an existing one, the road authority must assess the road, its level of use and the surrounding environment.
“They’ll consider the road function and level of development, as well as activity around the area in question,” Charles says.
“Authorities take into consideration whether the road is near key traffic and pedestrian hotspots such as schools, shopping centres and industrial or agricultural areas.
“On regional roads, the presence of farms and agricultural land is taken into account before speed limits are set, as well as the way in which residents access the land and how many road users travel through the area.”
Other considerations include the road’s quality, function, features, geometry, crash history and connected driveways and intersections. “The number of lanes and the width of them, along with road shoulders, bike paths, footpaths, curves and crests all influence how speed is managed,” Charles says.
“The number of driveways, intersections and roadside hazards such as power poles, trees and embankments also play a part in what speed limit is set.”
This is just one of seven physical crash tests ANCAP undertakes to reproduce the most common on-road crash types. This includes side-impact and run-off-road crashes, rear-end collisions and pedestrian incidents. ANCAP tests the impact these crashes have on both adults and children using its family of dummies.
Along with the physical crash tests, ANCAP also undertakes more than 600 active safety tests. These tests assess the effectiveness of a vehicle’s safety assist collision avoidance technology, including emergency-braking and lane-support systems and automatic emergency steering. In 2023, ANCAP broadened its assessment to include scenarios where a car encounters a motorcyclist and a child pedestrian.
King William Rd, Unley.
Why 40km/h?
The default speed limit in built-up areas has been 50km/h since 2003. However, in 1999, the City of Unley became the first council in Australia to introduce 40km/h speed limits across its entire local street network. It also recently dropped the speed limit from 60km/h to 50km/h on Unley Road between Greenhill Road and Park Street.
Several other councils – including Charles Sturt, Prospect, Mitcham and Burnside – have since adopted reduced speed limits in certain local areas.
Charles says the 40km/h speed limits aim to create safer conditions for all road users.
“The 40km/h speed limits have been introduced in areas where it’s more appropriate than the default 50km/h speed limit or signposted 60km/h speed limit,” Charles says.
“Residential areas and busy commercial precincts benefit from the lower limit due to a combination of narrow streets, increasing residential density, on-street parking, frequent driveways and pedestrians.
It also provides a safer environment for cycling, particularly where it’s not possible to provide bicycle lanes.”
"They (residents) felt it was dangerous for their children to be anywhere in their front yard and when reversing from their driveways there were a fair few near-misses..."
- Jassmine Wood
Making change
Picture this: There’s a road near your home where the speed limit is 80km/h, but for various reasons – including safety – you think it should be reduced to 60km/h. Your neighbours agree and you raise your concerns with the local council and the State Government.
After a lengthy process, the State Government decides to reduce the speed limit to 60km/h. This was the reality for many West Beach residents who wanted the limit reduced on Tapleys Hill Road between Africaine Road and Sir Donald Bradman Drive.
RAA, along with DIT, undertook a comprehensive review of the speed limit on this section of the road. The findings suggested that lowering the speed limit could improve overall safety with minimal impact to travel times along the stretch of road.
West Torrens Deputy Mayor Jassmine Wood (pictured) says local residents lobbied both the local council and the State Government to reduce the speed limit along Tapleys Hill Road.
“They (residents) felt it was dangerous for their children to be anywhere in their front yard and when reversing from their driveways there were a fair few near-misses,” Jassmine says.
“Living on Tapleys Hill Road, residents witnessed a number of quite serious accidents so they felt the speed limit was too high for the road. “Ultimately, the State Government owns the road, and the minister decided to reduce the speed limit from 80km/h to 60km/h.”
So, there you have it. That’s how speed limits are decided and altered, depending on the road and conditions.
West Torrens Deputy Mayor Jassmine Wood.
Do you have a speed limit question?
Speak to RAA’s road safety experts on 8202 4517 or email roadsafety@raa.com.au
IMAGES: Getty; RAA/Mike Lockheart.
