Germany’s autobahns have almost mythical status: a network of high-quality, efficient motorways criss-crossing the country where you can drive as fast as you want.
Want to drive 300kmh?
You can (although it’s not recommended—there is an ‘advisory’ limit of 130kmh and limits in some areas).
With Australian motorists limited to a more pedestrian 100kmh to 110kmh, it does raise an interesting question: could our highway speed limits be raised?
Afterall, speed limits on our highways are lower than those in many other countries.
European countries such as France, Italy and Spain all allow drivers to reach 120kmh-130kmh, while 70mph (113kmh) is permitted on motorways in the United Kingdom.
In the United States, speeds vary by state, however many states set rural freeway limits between 70mph (113kmh) or 80mph (129kmh). Things get even quicker on State Highway 130 in Texas, where motorists can cruise along at 85mph (137kmh).
Of course, it isn’t quite as simple as looking at overseas speed limits and applying them here – there’s a world of difference between the UK’s motorway network and remote, unsealed rural highways in Australia.
How dangerous is speed?
But before we debate speed limits, let’s look at the relationship between speeding (which is either exceeding the limit or driving faster than conditions allow) and road accidents.
According to the NHTSA (National Highway Traffic Safety Administration), speeding is involved in one-third of motor vehicle fatalities in the United States.
Faster speeds mean faster collisions, which in turn mean safety equipment is less effective and impacts more severe. Crashing at 100kmh generates force equivalent to driving off the roof of a 12-storey building—enough to cause fatal internal injuries.
The faster motorists drive, the less time they have to react to changes and the longer braking distances become (every 5kmh above 50kmh adds five metres stopping distance), reducing ability to avoid accidents.
There are other downsides to speeding: internal combustion engine powered vehicles are optimised for driving between 50kmh and 80kmh. At higher speeds, both carbon emissions and fuel costs are higher.
Wrapping those factors up, Nilsson’s widely cited ‘power model’ found that a 1% increase in average speed results in approximately a 2% increase in injury crash frequency, a 3% increase in severe crash frequency, and a 4% increase in fatalities.
So, what does this mean for speed limits?
Research by the International Transport Forum looked at the link between speed limits and casualties in ten countries where speed limits were either increased or decreased. They found that in “no case did an increase in mean speed coincide with fewer crashes or causalities”.
Put simply, higher speeds mean a higher road toll.
Not so fast… is it really that simple?
In theory, speed plays a role in all accidents.
If every kilometre an hour quicker increases the risk of crashing, then reducing fatalities towards zero could be achieved by dropping speed limits towards zero.
After all, Nilsson’s Power Model suggests halving speeds could reduce fatalities five-fold.
But while dramatically lowering limits would reduce fatalities, authorities are unlikely to go to such lengths. Why? Because speed limits are not designed to prevent all accidents.
Rather, they must balance a range of social, economic and safety considerations. These can include the type of road users, road infrastructure and surrounding environment, types of vehicles, and the safety, amenity and economic needs of the community, and personal freedoms.
There is an inherent risk that comes with driving (it’s one of the leading causes of death in Australia) but this is a risk accepted by drivers and occupants for the ability it brings to travel long distances quickly, affordably, and conveniently.
What else do we need to consider?
Today’s maximum speed limits were largely set in the 1970s, before many modern advances in automotive safety.
In 2021 there were 1,123 fatalities on Australian roads, compared to a peak of 3,798 in 1970, which was also the deadliest year per capita. That year there were 30.4 fatalities per 100,000 population - six times the current rate.
Emerging technologies promise to make our roads even safer. Self-driving cars, AI monitoring to detect weary drivers, and technology to predict accidents and dispatch first responders may all further reduce the road toll.
Road infrastructure also plays a role. Best practice dual carriageways with wide shoulders, long on/off-ramps, barriers to prevent head on collisions, and high-visibility signage and lighting can be made even safer by variable speed limits (already employed on many Australian roads) and other ‘smart motorway’ technology.
This is where Australia’s vast distances present a problem—it’s much harder to keep our sparse, 800,000 km road network built and maintained to a gold-plated standard than can support higher speeds than it is for nations with smaller, denser road networks
This is why many proposals for increased speed on Australian roads are centred around specific highways such as the Hume between Sydney and Melbourne. Proponents argue that the Hume’s wide lanes, gentle curves, smooth bitumen and long on/off-ramps could support 130kmh while better connecting our two largest cities and warding off fatigue.
Speaking of fatigue, research by QUT found fatigue was the primary contributing factor to 30% of fatal accidents in regional areas. While less than one-third of Australia’s population lives in regional areas, accidents on rural roads represent two-thirds of fatalities. A speed limit of 130kmh compared to 100kmh could shave over two hours off a 1,000km trip.
Those higher speeds may also bring other benefits. When the UK raised speed limits for HGVs (Heavy Goods Vehicles) by 10mph in 2015, analysis found that every 1mph increase would free up 650,000 driver hours and save £10 million a year.
In Denmark in 2004, speed limits were raised from 110kmh to 130kmh on half of the motorway network. While road injury accidents fell on both (partially as a result of increased enforcement measures and infrastructure upgrades), they dropped by a much greater rate (-33% vs -8%) on the roads with 110kmh limits.
Closer to home, unrestricted speeds were allowed on a 300km stretch of the Northern Territory’s Sturt Highway for a seven-year period before a 130kmh limit was introduced. During the restriction-free period, there were no fatalities—the only injury reported was attributed to alcohol consumption.
And what about the autobahn? It’s often said that the autobahn carries about a third of German traffic but is responsible for one-tenth of fatalities. By that measure they’re safe, but it obscures the full story: the risk of death on a German motorway is twice as high as a British one, while deaths are 25% higher on unrestricted sections of autobahn.
Are we ready for higher speed limits?
There is a direct relationship between speed and frequency of accidents, and between speed and the likelihood of injury or death in an accident. Raising speed limits nationwide would increase the road toll.
But speed limits are set to meet a range of competing priorities, and speed is just one of many factors in determining the likelihood and severity of an accident.
As such, where quality highway infrastructure exists—dual carriageways with dividing crash barriers, hard shoulder lanes and smart technology for example—it may be possible to utilise variable speed limits to allow increased limits in certain favourable conditions.