Why we need to look at Travel Behaviour differently now

I HAVE CONSIDERED the question of how travel behaviour change can support progress towards decarbonisation in some of my commentary columns in LTT and TAPAS in past months, and in previous books intended for non-specialists. I have now developed my thinking on these issues in my new book, ‘Travel Behaviour Reconsidered in an Era of Decarbonisation’, which is aimed at transport professionals – practitioners, analysts and academics. I examine both arguments and evidence in detail, with full references. At its core is a critique of orthodox transport economic analysis and modelling, along with proposals for fresh approaches to address the new circumstances with which we, and our transport systems, are now grappling.

I argue that the need to reconsider travel behaviour and its analysis is two-fold. First, decarbonising travel could be achieved both by new technology and by altering behaviour so that we make less use of the car. The question for consideration is whether such behaviour change is feasible in practice on a scale that would make a useful contribution.

Second, I argue that there is a need to reconsider the economic analysis of transport investment so that this reflects the observed travel behaviour of real people in the real world, as opposed to assumed behaviour of utility-maximisers functioning within constrained analytical frameworks, the orthodox practice.

Behaviour change

To set the scene, the first chapter of the book outlines the pattern of travel on Britain, largely based on findings of the National Travel Survey prior to the pandemic. (UK data is particularly extensive, but I refer to other countries where possible.) The main feature, of course, is the dominance of car travel, which brings with it a variety of problems familiar the LTT and TAPAS readers. Yet the attractions of the car tend to be underestimated by those who hope for a shift to public transport and active travel. The car provides convenient door to door travel over short to medium distances where road traffic congestion does not cause excessive delays and parking is available at both ends of the trip. These conditions may not be satisfied in city centres, where public transport can be provided most economically and where catchment areas, whether for schools or supermarkets, are tighter, making active travel more feasible. But beyond city centres - in the suburbs, towns and rural areas - alternative to the car are much less attractive and mode shift much more difficult to achieve.

Travel mode share (%) in England 2019. Source: NTS table 0409. Taxi and other private transport omitted.

Average travel distance, time and trips per person per year in Britain. Source: National Travel Survey, table 0101.

Yet the car is not attractive just for its utility; there are also ‘feel good’ factors that prompt car ownership and car-dependent lifestyles. Witness that cars are parked for 95% of the time, a good economic argument for car sharing, but conversely an indication of the value placed on private ownership. Witness also the growth ownership of SUVs, not least in urban areas where there is little practical need for a large 4x4 in place of a traditional smaller hatchback. The motor manufacturers are naturally focused on satisfying such feelings; and governments are supportive of auto industries for reasons of industrial and employment policies.

In the third chapter of my new book, I outline the important consequences of the coronavirus pandemic, a ‘natural experiment’ that showed how digital access could substitute for physical access under ‘lockdown’. Yet once the restrictions were lifted, car use returned quickly to pre-pandemic levels, consistent with the attractions of the car for gaining physical access to people and places, activities and services.

Chapter 6 discusses the routes to transport decarbonisation. For surface transport, electric propulsion is by far the most important means, though the equivalent in aviation is much more difficult. Some analysts and policy makers argue for a substantial reduction in car use as well, for instance by 20% as soon as 2030. But because of the attractions of the car, and given the built environment we have inherited within which trip origins and destinations very largely arise, any such reduction reflects much wishful thinking. The best prospects are in city centres where rail in all its forms provides speedy and reliable travel compared with cars, buses and taxis on congested roads. But urban rail is costly and takes a long time to build. Cycling infrastructure is much cheaper and quicker to implement, but largely attracts people from public transport, not from their cars.

So the prospects seem quite limited for changing travel behaviour and reducing car use on a scale that would make a useful contribution to decarbonisation objectives. How did we get to this state?

Changing travel trends

The historic trends in travel behaviour, the successive changes that have occurred, and their implication for future demand, are at the heart of what the new book explores. The evidence presented in the second chapter suggests four eras of travel: first, early man came out of Africa to populate the habitable earth, walking for 3-4 hours a day, covering around 3000-4000 miles on average, hunting and gathering. Then, starting 12,000 years ago, settled farming communities came into being, when average daily travel time fell to about an hour a day, covering about 1000 miles a year at walking speed (horse drawn vehicles on poor roads were not much faster).

The third era began in 1830 with the opening of the first passenger railway, between Manchester and Liverpool, utilising the energy of coal to travel faster than walking pace. Oil in the twentieth century permitted mass mobility through the internal combustion engine employed for road vehicle propulsion, as well as air travel. And the modern bicycle harnessed human power for local trips at faster than walking pace. According to the National Travel Survey, the average distance travelled in Britain increased to reach about 7000 miles per person per year by surface modes by the end of the twentieth century, with average travel time invariant at an hour a day. But then growth ceased, in part the result of exhausting the scope for faster travel through refinement of established technologies. This was the beginning of the fourth era of travel, that driven by the need for decarbonisation.

Each of these past innovations in transport technology based on fossil fuel energy led to a step-change increase in the speed of travel, and in turn to increased distance traversed in the long-run invariant hour a day of daily travel. Hence the benefits of faster travel were taken in the form of greater access to people and places, employment, services and activities, to family and friends, with the enhanced opportunities and choices that improve our quality of life.

In contrast, the new transport technologies seem unlikely to result in increases in speed of travel or of access. Electric propulsion is important for decarbonisation but does not increase the speed of travel. Digital platforms, exemplified by the access readily provided to car travel by the likes of Uber, and digital navigation, known in the road context as satnav, improve the quality of the journey without increasing speed. And automated vehicles on roads shared with conventional vehicles seem unlikely to permit faster trips. So these, the main new technologies, will not increase access benefits to users of transport networks.

A second reason why the growth of average daily distance travelled ceased to increase at the turn of the century, is evidence that those with the availability of a car in the household or good public transport services have arguably adequate levels of access, choices and opportunities, such that there is no need to travel further. Hence demand can be said to be saturated, a general feature of mature markets, and with no reason why travel should be an exception. However, travel to permit access has two distinct characteristics. First, improved access to any given class of destination is subject to diminishing returns, a standard economic concept. And second, access increases with (up to) the square of the speed of travel, reflecting elementary geometry. The combination implies that per capita travel demand for the purposes of access may be expected to saturate, consistent with the findings of the National Travel Survey and other sources.

Percentage share of travel by car, trains and buses in Britain (passenger-kilometres). Source: Transport Statistics GB, table 0101.

While per capita travel has ceased to grow, the UK population is increasing, which requires consideration of how this may propel travel demand growth. Much would depend on where the growing population would be housed: new homes on greenfield sites would increase car use, whereas accommodating population growth within existing urban areas would point towards improvement of public transport services to meet the associated transport needs. The scale and location of new homes is currently a major issue of national policy, yet to be settled.

So the fourth era of travel is characterised both by the lack of new technologies to travel faster, and by substantial travel demand saturation, both helpful to implement transport decarbonisation. Yet population growth accommodated on greenfield sites is unhelpful. Overall, the scope for a significant reduction in travel demand seems quite limited.

Appraisal and modelling reconsidered

The second core theme of my book – decision-making processes for transport investment – leads to a fairly detailed critique of conventional transport economic appraisal which is based on the supposition that the saving of travel time is the main benefit of investment in new capacity. My conclusion is that it has not been possible to achieve a self-consistent methodology in this territory even after some sixty years of effort. One consequence is a mismatch between the policy objectives of many high-profile investments and the conventional estimation of economic benefits, which is therefore suitably massaged to align with the policy.

At the same time, there has been growing general recognition that the main benefit of investment that allows faster travel is increased access. However, attributing monetary value to access has proved difficult conceptually, and has not been successfully developed into a methodology for practical application. Besides, as noted above, travel demand for the purposes of gaining access is subject to saturation, quite unlike demand based on the supposition of time saving, which means that the latter cannot be a proxy for the former.

Identifying the benefits of investment as enhanced access creates problems for transport modelling, another issue I explore in some depth in the new book. Transport models to justify major investments typically comprise two parts: a variable demand multimodal traffic model, the outputs of which are inputs to an economic model that allows estimation of monetary benefits, comparing the with- and without-investment cases, and hence yielding the benefit-cost ratio, important for the decision to invest. Yet benefit in the form of increased access cannot be accommodated by the economic model as it exists, on account of the assumption of transport economists that time savings are the main benefit. This therefore requires the traffic modellers to constrain model outputs to a counterfactual case in which travel time is saved, rather than used to travel further for greater access, disregarding the increased vehicle-mile-related externalities and land use change that arise in reality. So transport modelling as currently practiced does not provide a secure basis for the estimation of investment benefits, nor of carbon and other externalities.

Fresh approaches

Pulling all these threads together, the final chapter of my book suggests some fresh approaches to travel analysis and transport policy, to respond to the methodological shortcomings of conventional appraisal and modelling that I identify, and to the need to make progress towards the Net Zero objective. I suggest a presumption that Britain has a mature transport system comprising the road and rail networks, consistent with travel demand saturation as discussed above. This is already the case for urban roads, where, in the last century, investment in increased capacity in the form of both new (often elevated) highways and enlarged carriageway for vehicles took place in response to growing car ownership; whereas more recently the trend has been to recover such capacity for active travel and prioritised bus routes. Demand for vehicle travel on urban roads must now be managed within constrained capacity.

There is a good argument for treating the interurban road network as mature, so not aiming to invest to increase capacity generally, hitherto justified by notional travel time savings. There may be benefits from particular investments associated with land use change; for instance, were a third runway at Heathrow airport to be built, investment in surface transport infrastructure would be needed to cope with increased passenger numbers, the resource implications of which should form part of the cost of the project as a whole.

More generally, location-specific road investment to make land accessible for development could be justified where the decision to develop is made jointly by planners, developers and transport authorities and where the developer contributes to the cost of the infrastructure. The case would be based more on commercial considerations than on orthodox welfare economics, although carbon emissions and other externalities should be taken into account.

Cessation of investment in a national road construction programme would be a big shift of policy politically, although this is what the Welsh government decided two years ago. But there is still widespread support for road investment among most politicians, national and local, the latter because the funds provided by central government are seen as ‘free money’. It is widely supposed that increasing road capacity reduces congestion, improves connectivity and boosts economic growth, although the basis for this supposition is tenuous. And of course, the construction industry and the consultancies that benefit from the funds that flow are also supportive. Nevertheless, there is a strong case for a switch in effort from costly investment in new civil engineering structures to making best use of the physical infrastructure we have. Economic analysis and modelling would then focus on the efficient management and use of the network, closely linked to the operational analysis of the road network in real time, a topic that has been neglected hitherto. To do this we now have the opportunity to take advantage of digital technologies that are already in wide use and are both scalable and relatively low cost.

Transport economic analysis has focussed on individual projects. In contrast, it has always been difficult to articulate an economically persuasive strategic case for a programme of transport investment. Regarding the transport system as substantially mature changes the main challenge from justifying a collection of investment projects to reconciling transport operations with the Net Zero objective.

The key elements of a strategy, whether of a particular sector or of transport provision as a whole, are:

• the switch to zero-emission vehicles for surface transport;

• employment of digital technologies to optimise network operations;

• and financial support for public transport.

Alongside these, any investment in new capacity should now be specifically justified case by case to support economic development, such decisions being taken jointly with planners and developers, and schemes funded in part by the developers, as beneficiaries.

Active travel is not included in my key elements of strategy, although it is a good thing in many respects, including health and environmental benefits - I myself am a cyclist. But I see limited scope for getting people out of cars onto bikes. Copenhagen is a city famous for cycling, but car mode share is only slightly less than in London, while public transport is half that in London. So you can get people off buses onto bikes, but harder to get them out of cars, even in a small, flat city with excellent cycling infrastructure and a strong cycling culture.

One reason is that in Britain 80% of carbon emissions from car journeys arise from trip of more than 5 miles, and 95% from trips of more than 2 miles, so only limited opportunity to get switch to cycling and walking respectively. I don’t therefore see promotion of active travel as a central element of a national transport strategy, although in cities with crowded public transport it may have more attractions, as in London, albeit with some loss of farebox revenue.

My book was completed before the General Election and the appointment of the new government. It will be interesting to see how their policies relate to my contention that a new approach is needed to transport priorities. I provide some initial thoughts on this in a postscript to this article below.