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Breaks in trend

David Metz Honorary professor, Centre for Transport Studies, University College London

18 October 2019/Categories: PTRC News


Breaks in trend

We have nearly half a century of time series data from the National Travel Survey that shows little change in both average travel time (close to an hour a day) and trip rate (about 1000 a year). In contrast, the average distance travelled displays two distinct phases: growth from 4500 miles per person per year in the early 1970s to about 7000 miles by 2000, after which growth ceased. Most travel is by car, so, as expected, car use per capita ceased to grow at the turn of the century, which is also the case for other developed countries. Such cessation of growth of car use has previously been called ‘peak car’, but a better term would be ‘plateau car’ since there is little evidence of a decline in per capita distance travelled.

Growth in average distance travelled was a consequence of higher speeds made possible by the growth of car ownership, supported by road construction. The proximate cause of cessation of growth in car use was the cessation of growth of household car ownership, which increased from 14% in 1951 to 75% by 2000, after which growth ended. A number of factors contributed to the break in the growth trend of car ownership. Population growth in cities, where alternatives to the car are viable, reflected both a shift in the economy from manufacturing to services that tend to be located in city centres, as well as the attractions of city living for young adults, whether studying or in employment.

In successful cities, exemplified by London, car use has been constrained by the capacity of the road network while the travel needs of a growing population have been accommodated by investment in rail. Increasing population density shrinks catchment areas for retail businesses and public services, so making active travel and public transport acceptable alternatives to the car. Car use in London peaked at around 1990 when 50% of all trips were by car, subsequently falling to 36% at present, with the Mayor’s ambition to reduce to 20% by 2041. Increasing population density gives rise to agglomeration benefits – economic, cultural and social – such that declining car use is associated with increasing prosperity. Other cities have a choice: whether to accommodate the car on account of its attractions as a means of mobility; or whether to push back the car to encourage interactions between people.

While car use per capita ceased to grow at the turn of the century, rail passenger numbers went in the opposite direction, doubling over a 20 year period, a consequence of the growth of employment in business services in city centres, congestion on the roads, and investment in the railway by both the private sector train operators and the public sector Network Rail.

The breaks in trend in both road and rail use pose problems for modellers and forecasters. Such breaks reflect changes in travel behaviour, hence historic relationships (elasticities) cannot be assumed to apply. Moreover, the invariance in average travel time observed in the National Travel Survey findings indicates that the benefits of transport investments are not time savings as conventionally assumed. Rather, people take advantage of higher speeds to travel further, to have more choice of destinations, services and opportunities. In short, the benefits of investment are improved access, which is generally subject to diminishing returns. So the conventional four-stage transport model that generates time savings as the output in ‘do something’ cases does not validly represent the changes in travel behaviour that result from an investment.

A feature of travel in the twenty-first century is the impact of new technologies. What impact may we expect on travel by old-established modes of the rapidly developing, often disruptive, digital technologies? Four new technologies are available, or becoming so. Electric propulsion eliminates tailpipe emissions, good for urban air quality and mitigating climate change. Digital navigation can improve the efficiency of our travel and reduce uncertainty and anxiety. Digital platforms allow more efficient matching of supply and demand, exemplifies by ride-hailing taxis such as Uber. And autonomous vehicles may reduce costs for conveyances that otherwise would have a human at the wheel, but may add to congestion as unoccupied private cars make their way to where they are next needed.

The past transport innovations – railway in the nineteenth century, motorcar in the twentieth, modern bicycle in its heyday, motorised two-wheelers in low income countries today – all these allowed a step change in speed and hence in access. In contrast, the new technologies seem unlikely to permit faster travel. Accordingly, they will not be transformational for users, but rather offer incremental improvements to the quality of journeys.

We are therefore in a period of relative stability in respect of per capita travel, which innovative technologies seem unlikely to disturb.

David Metz’s new book, ‘Driving Change’, is priced at £19.99 and is available from the publisher with a 20% discount quoting promotion code AF2019 https://www.agendapub.com/books/78/driving-change  

Also available from Amazon.

 

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