Reviewing the Factors Contributing to Car Traffic in Britain

London traffic

Background

In the last 10 to 15 years the rate of car traffic growth has been declining in Britain and it is not clear why. Understanding factors behind this trend can help policymakers plan for future infrastructure needs.

Goals

The aim of this rapid evidence assessment was to gain a better understanding of the recent levelling off in total miles driven in Britain by reviewing evidence on the possible contributory factors.

The primary aim of the review was to identify and present findings covering the extent to which technological, social, economic, demographic, political, geographical and environmental changes have affected car usage and ownership. Evidence is presented on key factors influencing driving within these areas, and about how they affect different demographic groups, when available.

The secondary aim, where evidence exists, was to explore further why a particular factor is important; for example, if an identified factor is that young adults are delaying licence acquisition and car ownership relative to young adults a decade ago, to explore what the reasons are behind this.

Methodology

The study undertakes a rapid evidence assessment review of peer-reviewed papers and ‘grey’ literature to provide a better understanding of the recent levelling off in total miles driven in Britain. The review focused on studies that used evidence for the UK or Britain, or international studies that used evidence from the UK or Britain alongside evidence from other countries.

As the levelling off in car traffic is considered a relatively recent phenomenon, the search was restricted to material from 1995 onwards. The search was also restricted to passenger demand studies and to studies that were concerned with travel by car.

Key Findings

We found that the literature reviewed for this study provided a good description of key trends influencing car mileage since the nineties, including:

changes in traditional economic factors, including fuel price increases, changes in vehicle use costs and income growth, that would be expected to influence car mileage levels;
reductions in driving levels for young people;
population increases in urban areas, where car ownership and car use levels are lower on a per capita basis (although the impact of growing population in conurbations and cities on overall per capita car mileage levels appears to be relatively small);
increases in (per capita) car travel levels for women, although women are still observed to drive less than men;
increases in (per capita) car travel levels for the elderly, although the elderly drive less than other population groups;
increased immigration levels (with migrants being observed to use their cars less than those born in Britain, even after taking into account the tendency of migrants to live in urban areas); and
reductions in company car ownership, and associated reductions in car mileage, particularly for men.

However, what is less clear is the contribution of each of these trends to overall car mileage levels, and what are the key drivers impacting these trends.

We found little information on how the following trends impact car travel: (i) employment levels or type; (ii) use of internet technology; (iii) substitutes, in terms of mode shifts or switching to new destinations; (iv) network supply effects, such as congestion; and (v) attitudinal changes.

We also found suggestions that car ownership and usage may be approaching saturation – that is to say, car ownership levels (per household) and the use of those cars have stabilised at some maximum level. However, the evidence for saturation of car usage relies on analysis of aggregate car trends, which do not adequately account for the significant changes in car travel patterns for different segments of the population.