I was invited to contribute to a special issue of the journal Urban Planning on the topic ‘Car Dependence and Urban Form’. The aim of the editors was to explore the scope for developments of urban form to reduce car use. I agreed to contribute a review of the evidence of drivers’ perspectives, because I sensed there is a mismatch between the general popularity of the car and the concerns about its adverse impacts held by many transport planners and academics, such that they would wish to see a reduction in ownership and use. The paper is here. The abstract is below.

Abstract:  The concept of car dependence includes both travel to destinations for which other modes than the car are not practical and preference for car travel even when other modes are available. While the concept has been a focus for transport analysts for some time, car ownership and use have continued to grow. This reflects the utility of the car for travel on roads where drivers do not experience excessive congestion and where there is parking at both ends of the journey. Local public transport and active travel only become generally attractive alternatives to the car in dense city centres where road space for car use is limited. Reduced car dependence is facilitated by city planning that encourages increased density, opportunities for which are constrained by the stability of the built environment. As well as utility for travel to achieve access to desired destinations, car ownership is also attractive on account of positive feelings, including pride, reflecting both self-esteem and social status. The positive feelings of the population at large towards car ownership are not consistent with the critical view of many analysts, a divergence in point of view that contrasts with the general acceptance of the need to respond to climate change, for which the purchase of electric vehicles is seen as an appropriate action. Rather than advocating measures explicitly aimed at reducing car dependence, a more effective policy approach would be to increase the availability of alternative modes while mitigating the detriments of car use.

The issue of the open access journal that includes my paper is published.

The research literature – papers on aspects of travel and transport in peer-reviewed journals – has burgeoned in recent years. There are more papers in established journals and new journals created, often on an open access basis whereby the researchers pay the cost of publication, rather than journals relying on Libraries taking out subscriptions. The commercial basis of these new open access journals is not always clear, but certainly some are operated by for-profit publishers. There may therefore be an incentive to relax standards in the peer-review process to generate more income, lessening the overall quality of the research literature, which accords with my subjective impression. Some of the not-for-profit open access journals appear to lack editorial oversight by academic researchers.

One feature of many recent publications is the theoretical modelling of a new technology. This may be useful where there is a clear practical need, for instance the optimal deployment of charging points for electric vehicles. Yet there is also extensive modelling activity in relation to the deployment of autonomous vehicles (AVs), where experience of on-road behaviour is extremely limited thus far. Because model outputs depend on assumptions about AV performance parameters, the conclusions of such studies are very varied and provide little in the way of useful guidance to practitioners and policy makers.

Another feature of the literature is the excessive formal analysis of survey findings, for instance of the responses to surveys of the expected impact of a new technology, such as AVs, whether of drivers or city planners. State of the art analysis is reported in tabular form, with statistical significance specified numerically. Rarely are findings reported as charts, bar charts or scatter diagrams, with uncertainty shown visually, which would make clear the common limited significance of the findings.

A further feature of the recent literature is the systematic review, in which formal search methodologies are employed to identify all relevant papers on a topic. One problem is that because of the deteriorating quality of the literature, it becomes difficult to see the wood for the trees, as every paper needs to be cited. Systematic review originated in the medical literature where the aim of such meta-analysis is to identify every relevant study of a condition or treatment, with a ranking by quality such that only the highest quality papers contribute to the conclusions of the review. But for transport studies, such quality ranking is not practical, in part because findings may be specific to particular locations or circumstances.

Another problem with formal searching of the literature is that relevant papers may be missed because of the difficulty of specifying appropriate search terms. A recent paper by a distinguished transport researcher addressed a topic on which I had published some years ago without mentioning my contribution. When I raised the matter, I received an apology that his search had failed to identify my papers.

I have noticed increasing reference in the recent literature to transport researchers as ‘scholars’, a term hitherto largely reserved for those working in the humanities. Generally, those involved in transport research have seen themselves as based in disciplines such as engineering, economics, planning and the environmental sciences. The purpose of research within such disciplinary frameworks has been to advance understanding and thereby contribute to practical solutions to the problems of the transport sector. We have not, I think, seen ourselves as primarily involved in developing a branch of knowledge through scholarship that focuses on the extant literature. Indeed, the inward-looking processes of scholarship are cluttering up the literature with findings of little use and thereby may be displacing contributions of more practical value.

For instance, I have been attempting, without success, to get published in a peer-reviewed journal a paper on Digital Navigation, by which I mean the combination of satnav, digital mapping and route guidance algorithms that are in widespread use by road users. Highways Magazine, read by practitioners, has published a short account of my analysis, but a fully documented paper seems not to fit the current fashion for what’s hot, as seen by journal editors.

I have a new paper on how time constraints affect our travel behaviour. The link to the journal is here. Some copies are free to download here. The manuscript is here. The abstract is below.

Considerable observational evidence indicates that travel time, averaged across a population, is stable at about an hour a day. This implies both an upper and a lower bound to time that can be expended on travel. The upper bound explains the self-limiting nature of road traffic congestion, as well as the difficulty experienced in attempting mitigation: the prospect of delays deters some road users, who are attracted back following interventions aimed at relieving congestion. The lower bound implies that time savings cannot be the main economic benefit of transport investment, which means that conventional transport economic appraisal is misleading. In reality, the main benefit for users is increased access to desired destinations, made possible by faster travel, which is the origin of induced traffic. Access is subject to saturation, consistent with evidence of travel demand saturation. However, access is difficult to monetise for inclusion in cost-benefit analysis. Consequential uplift in real estate values may be a more practical way of estimating access benefits, which is relevant to the possibility of capturing part of such uplift to help fund transport investment that enhances such access.

It can be hard to get reviews of new books of any kind, given the large number of books published and the limited number of journals etc that publish reviews. So I was pleased to see a generous notice of my recent book, Driving Change, in the Journal of Transport Geography: ‘a very readable, engaging and thorough investigation of the factors that have driven travel change in high-income countries so far, with the aim to determine what will drive change in the future.’

For the full review Driving Change J Trans Geog review

I have a new paper published in a special issue on the future of urban transport and mobility systems in the journal Urban Science. This is an open access journal, so the paper is available to all.

The question addressed is the likely impact on autonomous vehicles on urban traffic congestion, a ubiquitous problem that has proved difficult to mitigate. My analysis concludes that little is changed until fully autonomous  (‘driverless’) vehicles are on the streets in significant numbers. There would then be two main consequences. First, by dispensing with the driver, taxis and other public service vehicles would cost less, which would increase demand, drawing people from conventional public transport, but at the same time offering an attractive alternative to personal car ownership in urban areas. Second, individually owned driverless cars would at times travel unoccupied, for instance returning to home for use by others in the household, having taken someone to work. Such unoccupied vehicles would add to traffic and their use might need to be regulated if they worsened congestion, to give priority to occupied vehicles.

There is much uncertainty about the feasibility and timing of driverless vehicles in urban areas, but it is not too soon to begin thinking about how policy should best be developed, to secure benefits from the new technology and mitigate possible adverse impacts.

Most air travel forecasts predict a long-term rise in demand, with limited consideration of any limits to growth. However for any given population there will be those who have not flown recently, as well as those who never have flown. For the UK, about half the population respond to travel surveys that they did not fly in the previous 12 months. We call these the ‘infrequent flyers’.

Little is known about this group, including  whether they are likely to fly in the future. Anne Graham, of the University of Westminster, and I recently published findings of an analysis of the characteristics of this group and the reasons for their travel habits, using a survey commissioned by the UK Civil Aviation Authority. We found that infrequent flyers make up a heterogeneous consumer group whose non-flying is influenced more by budget constraints and personal circumstances than specific aviation factors such as fear of flying.

The proportion of infrequent flyers in the UK population has remained stable over time. Our findings do not suggest that this is likely to change in the future, so the infrequent flyers are unlikely to be a source of future demand for air travel on account of their increased propensity to fly.

Our paper: Graham&Metz JATM Infreq flyers published

I have a new book published on 1 September, one in a series of short books on policy and economics topics described as ‘essays on big ideas by leading writers’. My contribution is a critique of the inconsistencies of transport policy in recent decades, which I attribute to the shortcomings of conventional transport economic appraisal in identifying the benefits that arise from investment. Readers of this web-magazine will recognise many of the arguments, now brought together in a single volume at a modest price.

The article below appeared in Local Transport Today 699, 10 June 2016. It was prompted by discussions at a workshop event organised by colleagues at the Transport Institute of University College London, who are carrying out a study for the Department for Transport of social and behavioural impacts of autonomous vehicle.

There is much interest in the possibilities for autonomous vehicles, in particular driverless cars. Focus is mainly on technological feasibility, role of the driver, risks and insurance. What has not yet been sufficiently considered is the implications for traffic. How much difference would autonomous vehicles make?

There are two broad routes to driverless cars. Mainstream auto manufacturers are equipping vehicles with devices that assist the driver. Adaptive Cruise Control automatically adjusts the vehicle speed to keep a safe distance from the vehicle ahead. Lane Keeping systems alert the driver if the car is drifting out of its lane and assist in steering back. Self-Parking systems allow a vehicle to park hands-free. Such devices are contributing to a reduced role for the driver, which ultimately could lead to driverless vehicles. The crucial transition is from high automation to full automation. Because many manufacturers, BMW for instance, market their cars on performance, they are likely to encourage hands-off-the-wheel only in situations where there is little challenge to the keen driver – such as long motorway trips or slow-moving urban traffic. Otherwise, driving is to be enjoyed.

Google’s pods, lacking a steering wheel, exemplify the other route – the great leap forward to full driverless. While these electric vehicles could be privately owned, they seem particularly suitable for shared ownership, given that they are, in effect, taxis with robot drivers. Taxis are popular, and we would make more use of them if they were cheaper, which they might be if robots replaced humans. This could increase demand, adding to traffic congestion in urban areas. But possibly the technology might allow the safe distance between moving vehicles to be reduced, packing more into the available carriageway.

The main impact on traffic of shared driverless cars is likely to be via parking. Privately-owned cars are generally parked for 95% of the time, seemingly an inefficient use of resources. Sharing would allow more time in use and so fewer parked cars. But the main impact on road space would be in the suburbs and car parks, not city centre streets where congestion is most acute and where parking is limited to avoid impeding traffic.

Driverless vehicles would contribute to congestion when they are on the move empty, as do black cabs plying for business. Programming your personal driverless car to cruise round the block empty while you transact business in a shop – in effect ‘parking’ on the move – would need to be regulated, possibly banned, in city centres (although this could lessen the attractions of driverless vehicles). A two-car family might economise with one driverless car, taking the breadwinner to work, then returning for use by the house wife/husband and children, before collecting the worker at the end of the day. But this would double the number of work trips, adding to traffic.

Altogether, it seems likely that the overall impact of driverless cars would be to increase urban traffic. It would be desirable model traffic flows under a variety of driverless scenarios to understand better the implications, since there may be conflicting policy objectives.

The UK Government is keen on driverless cars. The ministerial introduction to the Department for Transport’s 2015 action plan, The Pathway to Driverless Cars, starts: ‘Driverless vehicle technology has the potential to be a real game changer on the UK’s roads, altering the face of motoring in the most fundamental of ways and delivering major benefits for road safety, social inclusion, emissions and congestion.’ The Chancellor of the Exchequer, in his 2016 Budget, made a point of announcing trials of driverless cars on the Strategic Road Network by the end of 2017.

It could turn out, however, that benefits of autonomous vehicles on inter-urban roads could be offset by increased traffic on urban roads. One way of mitigating such traffic would be to increase vehicle occupancy significantly. This may be possible though what might be termed the ‘shared-squared-driverless’ mode, involving both shared ownership and shared use.

So rather than one or two occupants, the aim would be to fill the vehicle at peak times with passengers travelling in the same direction. This would reduce urban traffic congestion through high occupancy requiring fewer vehicles, with one study suggesting that this could remove 9 out of 10 cars in a mid-sized European city. Uber has introduced uberPool, a shared taxi service with lower fares, and uberHOP, which facilitates sharing along commuter routes at peak times. Their success will depend on the ability to match enough passengers going in the same direction, and also on the willingness of people to share.

If priority were given to shared-squared-driverless vehicles through road pricing or similar demand control measures, it might be possible to avoid urban traffic congestion while offering speedy and reliable door-to-door travel. This would be facilitated by some central oversight of such vehicles to minimise conflicts and maximise efficient use of the road network (analogous to air traffic control). The outcome could allow the car to compete with rail in urban areas, in terms of speed and reliability, and could help cities without rail infrastructure better to meet the mobility needs of their citizens. However, the technological, institutional and commercial challenges to the shared-squared-driverless concept are substantial, and practical feasibility is unclear.

Colin Buchanan’s seminal report, Traffic in Towns, was published 50 years ago, decades before the possibility of driverless cars. How much difference would autonomous vehicles make to urban traffic congestion? In the medium term, congestion could worsen, unless action were taken to regulate the movement of vehicles without occupants. In the longer term, the possibility of higher vehicle occupancy offers the prospect of mitigating urban traffic congestion.