Driver Knowledge Tests

Should New South Wales increase its speed limit?

Our maximum speed limit in New South Wales is 110kph. This is fairly standard in many countries. Some, like New Zealand, have a limit of 100kph, some also have 110kph such as many eastern European countries, while others have 120-130kph as their limit, such as Italy, Switzerland and Netherlands. the Northern Territory has four highways that have a limit of 130kph.

There are countries with lower speed limits and they tend to be where the roads don’t support it (e.g. poor infrastructure or lack of high speed roads) or the weather doesn’t support it (usually because of snow and ice). Only one territory has no speed limit (Isle of Man) and three¬†countries have some roads with no speed limits (Libya, Australia [part of the Stuart Highway in NT] and Germany [some autobahns]).

Our speed limits were set back when no vehicles had anti-lock brakes or air bags, and when passive safety features such as automatic braking weren’t even conceived. Modern cars are supremely more capable than older cars and this is what has driven the majority of the reduction in the road toll despite there being a huge increase in the number of vehicles on the road.

So, we could look at our improved vehicle specifications and justify raising the limit because vehicles are more capable, but there’s more to it than that.

Disadvantages of increasing the speed limit in New South Wales

If we chose to increase the speed limit to 120-130kph in line with many European countries, what could happen?

Increased traffic jams

It sounds counter-intuitive, but above a certain speed, traffic jams increase. The speed difference between timid drivers and aggressive drivers increases causing the timid drivers to drive more timidly, making things slower, and the aggressive drivers to brake more erratically, causing ripples of traffic jams (jamitons) back behind them.

There’s a theoretical maximum number of vehicles that can pass along a road safely while observing a two-second gap, and once this is exceeded, traffic tends to slow down. It doesn’t matter how fast traffic is flowing because drivers tend to leave 1.5-2 seconds between themselves. Therefore, in any one minute there will be a maximum of 40 cars that can pass any given point per lane, and the faster the vehicles are going, the more sparse the vehicles are on the road because they have to be further apart to maintain the 2 seconds between themselves. If anything adjusts this perceived safety buffer, e.g. a vehicle merging or moving into the lane, drivers will slow down to preserve the gap.

Merging becomes harder when the motorway traffic is going faster. A vehicle entering the motorway has to get up-to-speed to match the speed of vehicles already on the motorway, otherwise those vehicles have to slow down which starts more jamitons.

Difference in speed

If all traffic flowed much faster there would be more buffeting for cyclists and motorcyclists. Pedestrians would find it more difficult to cross roads. Vehicles travelling quickly would have less chance to react to other vehicles ahead that had slowed suddenly and unexpectedly.

It’s unlikely that the speed limit would be increased for large trucks which would cause a larger differential in speed.

Wildlife

We have a lot of large, heavy, bouncing meat missiles that have very little respect for the trajectory of a car. Hit a kangaroo at 110kph and it can be serious; hit it at 140kph and it can be catastrophic.

There are also other animals which are likely to be killed more frequently that are more endangered, perhaps less so in NSW and more up into Queensland (e.g. cassowary)

Tyre blowouts and brake failures

Great speed increases the risk of vehicle failure. While vehicle failure doesn’t contribute a huge amount to the road toll, increasing the speed that vehicles are allowed to travel at will cause extra wear and tear.

Driver skills

Many drivers do very little high speed motoring as they are stuck in rush hour for the majority of their driving time, or they live in the cities and that means pootling around at 50-60kph. Raising the limit to 130kph doesn’t mean that these drivers are equipped for it.

Fuel economy

Most cars are optimised to give the best fuel economy at between 80-90kph. The faster we drive above that, the more fuel we use. Given the current worries about our carbon footprint, increasing the limit doesn’t make sense from an environmental point of view.

Balance of trade

We import fuel, so saving it improves our economy.

Noise

Vehicles travelling faster create more tyre noise and more engine noise (because of the higher engine revs). This can impact residential communities close to the roads.

Use of inappropriate speed will increase

While 120-130kph might be fine in dry weather, it might be inappropriate in wet weather, but with a fixed limit we leave it up to drivers to decide.

Advantages of increasing the speed limit

Using a variable limit only when the weather conditions and prevailing traffic density supported it could improve travel times without compromising safety.

Increased productivity

Travelling faster means you get to where you’re going more quickly. This could improve productivity in some sectors.

Quality of life

Some people enjoy driving faster and feeling like they are getting to their destination more efficiently. This could improve their quality of life.

Fewer fines and less enforcement cost

A portion of people travel just above the speed limit because it feels natural to do it; they drive to the conditions and their personal (perceived) abilities. Some of these people will not increase their speed just because the speed limit increases, and therefore these fall out of the pool of people who are likely to be stopped for speeding.

Overtaking is safer

If drivers can go faster when overtaking a slower car it means less time exposed to danger.

Could higher limits work?

In some circumstances higher limits could be beneficial if they are introduced as variable limits only when the conditions are perfect. The roads must be separated by a barrier, wide, have good run-off and breakdown areas, be fairly flat and have excellent visibility. The weather must be dry and the traffic volumes fairly light.

Darren is an expert on driving and transport, and is a member of the Institute of Advanced Motorists

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