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Look forward to more congestion

Road congestion is not only annoying but expensive, costing $16.5 billion in 2015 and forecast to nearly double by 2030. Some say autonomous vehicles (AVs) will help reduce congestion. But evidence suggests they could also make it worse. Without careful planning, we may even look forward to more congestion.

Transition to AVs

Accounting firm KPMG says congestion will increase during the transition period to AVs. This is partly because AVs can travel within a few centimetres of each other without hitting one another, increasing the capacity of lanes by 10 to 25%.

In fact, dedicated driverless lanes could handle up to 4,000 cars an hour.

AVs would allow more people who do not usually drive to move around in cars, including children, the elderly and people with disabilities. People might also worry less about congestion because they can work, relax or sleep during journeys. Perhaps longer distances and travel times will become acceptable and even increase the frequency of car trips.

As these vehicles would spend longer on the road, they could boost demand for more road infrastructure. It depends very much on whether we own or share these vehicles.

Owned AVs

Privately owned AVs would “significantly exacerbate congestion” and demand for roads in 2046 (28 years hence). KPMG estimates this would lead to 29% longer average car trip times and 23% longer distances travelled.

There is evidence that even ridesharing does not take cars off the road. In New York City, ridesharing of privately owned cars seems to have increased demand for roads. Patronage of subway and bus services fell in 2016-17 while more people took car rides from Uber and Lyft.

Spanish toll road operator Cintra says (or hopes) private ridesharing could harm public transport, rather than “going against congestion and the tollroad business”.

Shared AVs

However, sharing but not owning vehicles, could have the opposite effect. For a start, there would be fewer vehicles and lower demand for roads. Eventually this would ease congestion.

KPMG forecasts a 7% reduction in average car trip times and 9% shorter average distances in 2046.

The shared option may be less popular with providers of infrastructure – or it could make existing infrastructure much more valuable. Existing toll roads may even gain scarcity value as AVs reduce demand for further toll roads.

More congestion

Meanwhile, KPMG admits “we know from experience that it is not possible to build our way out of congestion with more and wider roads”. This is primarily because people will use the new, faster roads in favour of the old ones until they become as slow as the old ones.

Railways still efficiently carry more people per hour per kilometre than a car ever can:

Number of people in one lane per kilometre per hour  
Heavy (light) rail 50,000 (20,000)
Bus on freeway (street) 15,000 (5,000)
Tram 10,000
Autonomous vehicle (AV) 8,000 (2 in each car)
Car on freeway (street) 2,500 (800)

Source: Curtin University.

Even so, the NSW government is determined to build roads. Westconnex, Beaches Link, Sydney Gateway, F6 and Western Harbour Tunnel, are all part of the grand plan to ring Sydney with toll roads.

So it seems we can look forward to more congestion and, by extension, more tolls.

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