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Travel demand: the basics

The long-standing relationship between growing incomes and increasing travel no longer applies

David Metz
21 March 2014
David Metz
David Metz
The number of trips we make each year and the time we spend travelling have remained steady for 40 years. Distance travelled grew sharply in the 1980s but has  fallen in recent years
The number of trips we make each year and the time we spend travelling have remained steady for 40 years. Distance travelled grew sharply in the 1980s but has fallen in recent years

 

The National Travel Survey (NTS) has been tracking the travel behaviour of residents of Britain for the past 40 years. All credit to the statisticians at the Department for Transport for their perseverance, which has generated the longest and fullest time series internationally. The NTS reports average per capita travel and covers all modes except international aviation – in effect personal daily travel.

The key NTS outcomes are shown in the graph. The average number of trips is about a thousand a year and has not changed significantly over the period. The average travel time in recent years has been 370 hours a year or close to an hour a day, and this has changed little over the 40-year period. What has changed is the average distance travelled, which was 4,500 miles per person per year in the early-1970s, rose to about 7,000 miles by 1995, and then levelled off (the recent dip is probably due to the sharp economic downturn). We also know from the NTS that journey purposes change little over time. 

So people have been making longer trips, in the same amount of time, with the same frequency. They have accomplished this by going faster, the result of investment – private investment in more and better cars, public investment in better roads, and public and commercial investment to improve the railways. But why travel further for the same purposes? The answer: to gain more access to desired destinations, to have more opportunities and choices. More choice of jobs accessible from where you live in the time you can spare for commuting, more choice of homes accessible from your workplace, more choice of schools, shops and so forth. Time limits daily travel, given the 24-hour day and all the necessary other activities. Going faster overcomes the time constraint.

Suppose you live in a village without use of a car, and where the public transport service is poor. Your choices are limited to those within walking distance. This is the position of many older and younger people in rural Britain today; was the position of most of us two centuries ago; and is the situation of millions in the developing economies. The introduction of a succession of transport technologies based on the energy of fossil fuels has transformed our lives by enlarging our opportunities.

The increased distance travelled allows us access to previously too distant destinations. This changes land use as locations hitherto inaccessible become accessible, with consequent enhancement of land values. Such land value enhancement as the result of transport investment is very visible in East London, where the Docklands Light Railway, Jubilee Line Extension and the Overground, with Crossrail to come, have catalysed regeneration. Public investment in the transport system has made brownfield land accessible, which has stimulated the private sector to develop new commercial and residential property that accommodates new jobs and homes. Moreover, the value of existing property is enhanced when access is improved. This has always been the main way in which transport investment contributes to economic growth.

Another current example that well illustrates the relationship between transport and land use is the scheme to develop the area in central London known as Nine Elms, which comprises extensive former industrial land along the river within a mile of the Houses of Parliament. The US Embassy is to relocate there, and plans are in place for major residential and commercial development. The area is to be made accessible by an extension of the Northern Line of the London Underground and a quarter of the cost will be funded by contributions from the developers, which they are willing to make because the feasible scale and value of the development would be much less without the access made possible by the Tube extension. More funding will be contributed by earmarking the higher business property taxes that are anticipated.

Such enhancement of land value is not taken into account in the standard approach to investment appraisal of transport projects, where typically three-quarters of the benefits are supposed to reflect the saving of travel time. Time spent travelling could be better used for more work or more leisure, both of which are valuable – this is the basis for valuing time saving from faster travel. However, as is evident from the NTS time series shown above, average travel time has changed very little as a consequence of investment in the transport system. This means that time savings are transient. In the long run, people take the benefit by travelling further, to have greater access, opportunities and choices. There is therefore a mismatch between the short-run nature of travel time savings and the actual benefits from investment in long-lived infrastructure.

A characteristic of land value enhancement is that it is observed as a location-specific market value. The benefits of investment in transport accrue to those who own property sufficiently close to the new or improved road or rail links. There can be windfall gains to owners favourably located. This suggests that it would be reasonable to seek contributions to capital cost from those who so benefit, as for example is happening in the case of the Nine Elms scheme. Reckoning benefits as time savings implies a much more distributed outcome, to travellers and their employers – but this is quite misleading.

The NTS time series shows that per capita distance travelled ceased to grow at about 1995. This implies that the historic relation between growing incomes and increasing travel has ceased to apply. Car travel accounts for nearly 80 per cent of the average distance travelled in Britain at present, so per capita car-miles has also ceased to grow. This cessation of growth of car travel is seen in most developed countries and is the phenomenon known as ‘Peak Car’.

Why has per capita travel and car use stopped growing? I suggest that this is because most of us – those with good private or public transport available – have sufficient access to meet our need for opportunities and choices. Access and choice increase with the square of the speed of travel because what is accessible is defined by the area of a circle whose radius is proportional to the speed of travel. However, the value of choice is subject to diminishing marginal utility – each extra choice being of less value than that preceding. This combination of characteristics implies a saturation function, consistent with what is observed.

For instance, 80 per cent of people living in urban areas of Britain have a choice of three or more large supermarkets within 15 minutes drive, and 60 per cent have a choice of four or more – pretty high levels of choice and little need to travel further for more variety.

The NTS data shows that personal daily travel in Britain has entered an era of stability. On average we travel for an hour a day and make a thousand journeys a year covering some 7,000 miles. This pattern has been established for nearly 20 years and there is little reason to expect much change. Forecasts of future travel demand should be based on continuity as the central projection or business-as-usual scenario. But the population is growing, which will increase total demand, as I will discuss in the next article in this series.  

This article is based on material included in a new book, Peak Car: the Future of Travel, available as an e-book from Amazon and in a print edition from Landor LINKS.

Specialist Transport Services Manager
Warrington Borough Council
Warrington
GRADE 13 (£58,797 - £63,735)
Specialist Transport Services Manager
Warrington Borough Council
Warrington
GRADE 13 (£58,797 - £63,735)
Specialist Transport Services Manager
Warrington Borough Council
Warrington
GRADE 13 (£58,797 - £63,735)
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