The evidence suggests new roads won't generate more journeys.

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It has been a commonplace view - supported in the past with some evidence - that building new roads didn't work as a strategy to reduce congestion because those roads encouraged new journeys. Indeed part of the argument here was that congestion itself acted to discourage car use and encourage shifts to other forms of transport.

So, when the government announces £15 billion of road investment, we get a familiar outcry:

The government claims the investment will be transformational, creating jobs and reducing journey times. But this is wishful thinking, ignoring the inconvenient truth that new roads create new traffic while dogmatically clinging to the assertion that road building is good for the economy.

The problem with this view is that, while it seemed to be true as car ownership soared and alternative travel options stagnated, it was never the roads that created the journeys - rather those roads acted as a justification for getting the car, then getting the second car and latterly buying the kids a car. However, since 2006 (or thereabouts) the game has changed with journey miles reducing. Partly this reflects recession and the cost of fuel - although journey miles increased during previous recessions - but mostly it reflects the impacts of other changes in our world.

How road use has declined in the USA

As this graph shows (I know it's from the USA but let's remember it's a much more car oriented culture) over the last decade there has been a steady decline in the miles travelled by car in the USA. The data for the UK doesn't show the same decline but slight increases in vehicle miles here are almost entirely down to light goods vehicles (LGVs - all those delivery vans plus the ubiquitous white van). And there is nothing to suggest that upgrading roads results in increases in vehicle miles. Even back in 2003 studies showed that the induced travel effect of new roads was lower than previously thought and that induced investment and induced growth effects were larger. Put simply the economic benefits of new roads has been under-estimated while the environmental disbenefits were over-estimated - with the result that investment was moved away from roads.

Since 2000 UK public investment in railways has increased from £3.5 billion per annum to £7.5 billion compared to a rise from £2 billion to £3 billion (not even keeping pace with inflation) in road investment. And we should remember that while about a fifth of the population use trains a lot, most people seldom if ever use this form of transport (buses are much, much more important than trains). But everybody - whether they own a car or not - uses the roads. So any strategic investment in our road network is welcome especially since about half the proposed investment is going into looking after the roads we've already got - something that governments, local and national, have neglected for decades.

Among the collectivists of this world there's a view that the private car is a bad thing (I seem to remember some daft Labour MP suggesting private cars should be banned). I take a different view - the availability of a car in the drive means that people are liberated from the inconvenience of public transport and the tyranny of its timetables. Talking to a senior council officer the other day, I discovered that there are places not three miles from the centre of Bradford that not only have no trains but, after 6pm, have no buses into the city.

However, regardless of my preferences (and the preferences of most Britons), the fact remains that the 'roads create traffic' argument lacks good evidence - road investment doesn't increase trips and does increase investment and economic growth. As Aaron Renn commented in talking about the graph above:

In fact, what peak car means is that while speculative projects may be dubious, there many be good reasons now to build projects designed to alleviate already exiting congestion. 

Bear in mind that by speculative projects Renn means privately-built roads predicated on toll income not simply new roads. The assumption that traffic growth had no limits was always the weakness in the 'green' argument against new roads but it's clear that as technology - smartphones, Skype, e-commerce and so forth - eliminates reasons for journeys the numbers of those journeys declines. And road investment really does become a stimulus to growth when it focuses on reducing or removing the congestion that pollutes and plagues our lives.

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