So what do we do about congestion?

The Government has announced its Road Investment Strategy that commits £15 billion expenditure over the next five years. One stated aim is a ‘free-flow core network, with mile a minute speeds increasingly typical’. How realistic is this?

Let’s consider the past pattern of travel behaviour that has been tracked over the past forty years by the National Travel Survey. Average travel time has stayed steady at about 370 hours a year, or an hour a day, a finding that holds true for all settled human populations. What has changed over the period is the average distance travelled, which increased from 4500 miles a year in the early 1970s to 7000 miles in the mid 1990s, since when this has grown no more. This increased distance in the unchanged travel time is the result of investment in the transport system that has permitted faster travel – private investment in cars, public investment in roads, and in railways.

People have taken the benefit of investment by travelling further to more distant destination, not by saving time in reaching unchanged destinations. This is contrary to what transport economists suppose when they estimate the main benefit of investment as time savings, valued for the extra work or leisure made possible. In reality, people travel further to have more opportunities and choices. For example, by travelling faster on the journey to work, you have more choice of jobs accessible from where you live in the time you allow yourself for travel, more choice of homes accessible from your workplace, more choice of shops, schools and so forth.

So people take advantage of road improvements that permit faster travel to make longer trips as part of their daily routine. This is particularly the case in areas where demand for housing exceeds supply, creating an incentive to travel further in search of affordable properties.

Daily travel is an important component of traffic on parts of the Strategic Road Network (SRN). Congestion on this network arises near to populated areas, where local users interfere with long distance users. Remote from populated areas, the traffic generally flows freely. If we add carriageway to a congested section of the SRN, it is the local users who take advantage of the faster travel to make rather longer trips, which generate extra traffic, and which restore congestion to what it was previously. Long distance users are no better off.

This is the basis for the maxim: ‘You can’t build your way out of congestion’, which from experience we know generally to be true.

So what do we do about congestion? Surveys of road users find that the main problem with congestion is unreliability, rather than increased time taken. We can tackle the unreliability problem by providing road users with good predictive travel time information before they set out, so reducing uncertainty in arrival time. This is becoming increasingly possible through digital technologies, which are far more cost effective than traditional civil engineering technologies in meeting the needs of road users.

So we can’t build our way out of congestion, but we can manage the problems arising from congestion far more effectively. To do that, we need a substantial reallocation of planned expenditure within the Roads Investment Strategy – from the civil engineering technologies of the twentieth century to the digital technologies of the twenty-first.

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David Metz

David Metz – Visiting professor at the Centre for Transport Studies, UCL