An independent Commission on Travel Demand, funded by UK Research Councils, recently issued its report, based on evidence and expert advice. There is no single message, other than that there are more uncertain factors influencing travel demand than conventionally supposed. However, the report make ten sensible recommendations for better processes.

I was disappointed that the report did not consider two matters on which I had submitted evidence. One is that demand for any kind of product or service may saturate, that is, cease to grow once all needs are met. For instance, ownership of many household goods, such as washing machines, exceeds 90%, so that demand no longer reflects growing tes, but only replacement plus population growth. There is evidence consistent with saturation of demand for daily travel for many purposes. For instance, 80% of the urban population of Britain have a choice of three or more large supermarkets within 15 drive minutes of home, and 60% have a choice of four or more. If you have a choice of 3-4 supermarkets within 15 minutes drive, you may not be inclined to drive further to have a choice of a fourth or fifth, in which case your demand for travel to supermarkets is said to have saturated.

Second, given that average travel time has not changed for at least the last 45 years, as measured in the National Travel Survey, increased travel demand (distance per capita) must require faster travel. This is now hard to achieve, given high levels of car ownership and the limited scope for this to grow, plus a mature road network where congestion proves difficult to mitigate. We have High Speed Rail on the way, but rail is a minority of all trips, so HSR would be a minority of a minority, with little impact on average speed.

The travel time constraint, coupled with the speed constraint, means that travel demand per capita is unlikely to grow significantly in the future. Total travel demand will be driven by population growth, of course, although the pattern of demand will depend on where the additional inhabitants are housed: greenfield means more cars, urban at higher density implies investment in public transport.

Professor Peter Jones, my UCL colleague, has been leading an EU funded project concerned with urban mobility, past and future, in five Western European cities – Berlin, Copenhagen, London, Paris and Vienna. The report is now available, as is a short speech by Peter.

A trajectory is identified in which cities start by attempting to accommodate the car, see the difficulties in high density locations and so reallocate road space to walking, cycling and public transport, and subsequently move on to focus on place – the role of streets as public realm for non-mobility activities. The figure above shows how car use peaked and then declined in consequence.

Recognition of place as an important quality of urban streets presents a problem for conventional transport investment appraisal, which only recognises the economic benefits of increased mobility. The report advocates ‘vision and validate’ as an approach, as opposed to the traditional ‘predict and provide’, using cost-effectiveness analysis to justify investment to attain the desired balance between mobility and place.

This report is a valuable synthesis of a considerable amount of data and analysis highly relevant to how we think about the future of cities.

 

I have a new article that reviews the evidence for the success of congestion charging (aka road pricing, road user charging) in the three major cities in which it has been tried. In London, there was a marked reduction in both car traffic and delays when charging was introduced, but delays reverted to previous levels by year five. In Stockholm, a similar initial impact was seen, but there was no monitoring of delays subsequently.

Singapore has been successful in using electronic road pricing to maintain desired traffic speeds, adjusting charges up or down according to whether speeds have exceeded or fallen below targets. However, this is only possible because there is a very high charge for vehicle ownership, which has limited this to 100 cars per 1000 population, compared with 450 in the UK and similar or higher figures for other developed economies.

Road traffic congestion occurs in areas of high population density and high car ownership. There are more trips that could be made by car than are in fact made. Some people are deterred by the prospect of time delays and make other choices: a different time or mode of travel, or a different destination, or not to travel at all. Measures that deter some drivers, such as congestion charging, reduce delays when introduced, which makes car travel more attractive to those who are more time-sensitive but less cost-sensitive, so that traffic increases and delays revert to previous levels. Accordingly, congestion is both self-regulating and difficult to reduce.

Although economists believe that road pricing is the proper way to tackle congestion, in practice the level of charges to make a useful impact would probably be too high to be publicly acceptable.

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.

In recent years there has been emerging evidence that the travel behaviour of young people has been changing, characterised by a shift away from car use. The UK Department for Transport commissioned a thorough study from researchers at the Universities of West of England and Oxford, comprising a literature review and secondary analysis of existing UK data sets.

The trend for young adults to drive less than previous generations began approximately 25 year’s ago. Driving licence holding by people aged up to 29 peaked in 1992-94, while car driver trips per person declined by 36% between 1995-99 and 2010-14. This decline is attributed to a variety of social factors outside transport, including more participation in higher education, more lower paid less secure jobs, and delay in starting families. Within the transport sector, the high cost of car ownership and more use of urban  public transport have contributed to declining car use. There is inevitable uncertainty about the future, but the authors conclude that is is difficult to envisage realistic scenarios in which all these future uncertainties combine in such a way as to restablish earlier levels of car use.
US experience
A recent survey of younger people (‘the millennials’, ages 18-34) in California aims to identify the factors that explain why they are found on average to drive 18% fewer miles than members of the previous generation. One report addresses lifestyle and attitudes, a second deals with residential location. Generally, the findings of the UK and US studies seem consistent.

For some years Michael Sivak, of the University of Michigan, has been monitoring vehicle ownership and distance driven in the US. His latest report shows that light duty vehicle ownership per person and per household both peaked in 2006, and that distance driven per person and per household reached their maxima in 2004. (Light duty vehicles are cars plus trucks with two axles and four tires.)

There has been some revival of distance driven per capita in recent years, but I would not expect any long term growth above the present plateau, given both time constraints on personal travel and speed constraints on the road network.

The National Infrastructure Commission has been consulting on a number of questions, including how  the Government could best replace fuel duty in a way that is fair.

 The prospect of a complete switch to electric propulsion for cars and vans will lead to loss of most revenue from fuel duty, currently about £28 billion a year (HGVs might still require taxable fuel), offset to a small degree by VAT of 5 per cent on electricity. Vehicle Excise Duty raises some £6 billion a year, rather less than the annual capital and current expenditure on national and local roads of £8 billion in total. So VED could be raised to cover the full cost of the road system. But that would leave a major gap in public revenues and would, in the long run, imply much cheaper motoring – welcome to motorists but problematic in respect of the detrimental impacts of the car.

To fill the revenue gap it would be logical to levy a charge on the use of electric vehicles (EVs). This would be a charge related to distance, weight of vehicle (which determines damage to carriageway), location and (possibly) time of day (reflecting congestion which imposes costs on other road users). It would also be possible to relate charges to the cost of the vehicle when new, so that the better off road users paid more than those who could only afford a reasonably priced family car.

The public rationale for such a charge would be that it is right that EVs should contribute their fair share of the revenues raised from road users, both to cover the costs of operating, maintaining and developing the road network, and to meet the wider needs of society.

EVs could only be charged for road use once their costs permitted this. At present, the lower cost of electricity goes part way to offsetting the higher capital cost of EVs. However, capital costs are expected to fall as battery technology advances, so that over time cost headroom will develop that will allow EVs to be charged for road use while maintaining their economic attractiveness in relation to conventional vehicles.

Devolution

Road user charging would allow devolution of revenue raising to fund the road system. One tranche of revenue would be taken by the Treasury to support general government expenditure. The remainder would be retained by road authorities to fund their expenditure on roads and other transport provision. The Department for Transport would decide charges for the Strategic Road Network, while local authorities with responsibility for roads would set charges for their networks. There would need to be some coordination of approach to minimise diversion of traffic onto unsuitable roads, perhaps a responsibility for the Office of Rail and Road.

Road authorities would set charges according to their revenue and investment needs: problems with potholes would justify raising charges, as would plans for additional capacity. The income stream from charges could be used to raise finance for capital projects. Devolution of revenue raising to road authorities would largely obviate the need for grants from central government, other than perhaps for regional ‘rebalancing’. If, like London, local authorities chose to manage demand by means of a congestion charge, the revenue could be used to fund public transport. This would provide an important tool to influence the pattern of urban transport.

The London congestion charge is well accepted by the public, is technically reliable and raises useful revenue. It is, however, based on a daily charge for entering the charging zone within the charging hours, regardless of level of traffic or distance travelled. The Mayor’s draft Transport Strategy indicates that consideration will be given to the next generation of road user charging systems, to help achieve policies for mode share, road danger reduction, environmental objectives, congestion reduction and efficient traffic movement. It would be sensible for consideration of technology options to be a joint effort between TfL and DfT, so that London could act as a test-bed for arrangements that are capable for national use in due course.

The technology for road user charging would comprise a digital platform with a vehicle-based device displaying an app. Other facilities could be offered on the device including route guidance to avoid congestion, journey time information, indication of available parking, facilities for sharing trips with those travelling in the same direction, and information about non-car modes of travel where these are practicable alternatives. The menu of options would trade off speed, quality and cost. This technology would allow the operation of the road network to be optimised, reliability to road users to be improved, and the costs of maintenance, operation and development to be recovered through charges that reflect costs.

The National Infrastructure Commission has been consulting on the intended National Infrastructure Assessment. One question concerns what changes to the design and use of the road would be needed to maximise the opportunities from connected and autonomous vehicles on both urban and inter-urban roads; and how could these changes be brought about.

Autonomous vehicles (AVs) are being developed by established car manufacturers and new technology companies. It seems unlikely that there will be much impact on road use until they become fully driverless, when there will be two main consequences.

First, for shared use vehicles such as taxis, the cost of the driver will be eliminated. This will open opportunities for services in the current gap between high capacity, low fare public transport and low capacity, high fare taxis. A variety of door-to-door mobility services using cars or minibuses will draw people from conventional public transport but also lessen the attractions of individual car ownership in urban areas.

Second, individually owned AVs will be capable of travelling unoccupied, for instance returning to base after dropping a passenger, or ‘parking on the move’ by circling the block while the owner is doing business. Such unoccupied trips would add to traffic and may need to be regulated in areas prone to congestion, to give priority to occupied vehicles.

As regards the impact of AVs on the capacity of the road network, the above consequences would be expected to increase demand and thus congestion. The question then is the scope for increasing capacity through connected autonomous vehicles (CAVs) operating with shorter headways, with or without drivers available for some tasks.

Trials are planned of platoons of freight vehicles, the main benefit being fuel saving from reduced air resistance. There will be drivers for each vehicle who will be trained and required to operate with a very short headway. However, the generality of drivers of AVs will be able to choose the gap to the vehicle in front. It is not clear why, without an incentive, they would choose a gap smaller than that with which they are comfortable, which may not be much different from current headways.

Accordingly, to increase road capacity by reducing headway there would need to be some incentive that would impact on individual drivers. This might be a road user charging regime that charged on the basis of the length of carriageway effectively occupied. However, drivers willing to ‘tailgate’ would pay less than those of a more cautious disposition, which would raise a question of public acceptability.

Another kind of incentive to reduce headway would be dedicated lanes that are less congested and faster flowing than other lanes, analogous to High Occupancy Vehicle lanes on US freeways. Short headways would need to be enforced. A faster lane for CAVs would need to be the outer lane, requiring vehicles to manoeuvre prior to leaving at a junction.

There would need to be acceptable incentives for drivers to reduce headways if manufacturers are to go beyond equipping vehicles with the existing adaptive cruise control. Manufacturers will be responsible for the safe functioning of AVs. Adding vehicle-to-vehicle or vehicle-to-infrastructure connectivity to reduce headway would exacerbate this responsibility by introducing functionality that depends on that of other manufacturers and suppliers and that increases the risk of security breaches.

More generally, connected vehicles operating at short headways would require reconsideration of the safety regime, which at present is concerned with the performance of individual vehicles, having regard to the nature of typical crashes. A system of connected vehicles would require consideration of fault modes at system level, for instance the consequences of faults in individual vehicles in a platoon and of faults in connectivity. It would not be surprising if there were trade-offs between headway and safety that limited the possible increase in capacity.

The Strategic Road Network (SRN) of motorways and major interurban roads is a mature system, with investment aimed mainly at increasing capacity by utilising hard shoulders as running lanes, plus junction modifications. Few wholly new routes of any length are planned. Mixed traffic will be the norm for many years to come. Distances between junctions are relatively short, compared with other countries. Space is scarce for forming up platoons of freight vehicles. So the SRN is not obviously well suited to pioneering short headway CAV operation, despite the Government’s enthusiasm.

Likewise, Britain’s urban roads substantially reflect historic street patterns, unlike more recent US gridiron layouts (of which Milton Keynes is a rare UK example). Narrow inner suburban streets with on-street parking are likely to prove awkward for driverless taxis, which would inhibit their general use.

Road traffic congestion arises mainly in or near areas of high population density and high car ownership, such that many potential car trips are deterred by the prospect of unacceptable time delays. Were capacity to be increased by connected vehicles operating with shorter headways, more car commuting would result, with more vehicles entering cities – not a desirable outcome given that car use is declining in successful cities. Increasing road capacity through vehicles operating at shorter headways is not fundamentally different from increasing capacity by adding carriageway. Through neither approach can we build or manage our way out of congestion.

Altogether, it does not seem a high priority for Britain to attempt to be an early adopter of connected vehicle technology. We should evaluate developments elsewhere, aiming to be a fast follower if there were to emerge benefits that could be gained under our conditions. On the other hand, there are good reasons to press forward with electric propulsion and digital technologies, including road user charging, where UK geography and institutions provide a favourable context.

The National Infrastructure Commission has now announced a competition with up to £200,000 available for ideas to change road design, management and use, to maximise the benefits of connected and autonomous vehicles. I will be interested to see if any proposals that result lead me to revise my somewhat pessimistic judgement.

In pre-Budget briefing, the Chancellor expressed enthusiasm for government investment to help get driverless cars on UK roads by 2021. In this he followed the example of his predecessor, George Osborne, who was keen that Britain takes bold decisions to ensure that it leads the world in new technologies and infrastructure. The Budget was followed by the launch of the Government’s Industrial Strategy, which featured new modes of mobility as one of four Grand Challenges, and stated that the Government wants to see fully self-driving cars, without a human operator, on UK roads by 2021.

There are two related reasons why the Government might attempt to ‘pick a winner’ of this kind: industrial policy and transport policy. If, as George Osborne claimed, driverless cars represent ‘the most fundamental change to transport since the invention of the internal combustion engine’, then support for autonomous vehicles should form part of our industrial strategy as well as our transport policy.

The Government has indeed been active in supporting trials and future deployment of driverless vehicles on British roads. Projects are underway in Bristol, Coventry, Greenwich and Milton Keynes; R&D is being funded; Codes of Practice for on-road testing published; and legislation introduced in Parliament to ensure that vehicle insurance covers both the motorist when driving as well as the car in automated mode.

There are two routes to driverless vehicles. The evolutionary approach, pursued by all the main international auto manufacturers, offers to relieve drivers of tedious tasks, for instance by means of adaptive cruise control, which regulates the speed and space to the vehicle ahead. The revolutionary route, pioneered by Google (now branded Waymo), dispenses with the driver entirely. Other US businesses with disruptive approaches are active developing driverless technologies, including Tesla and Uber.

With the enormous worldwide effort underway, it is going to be difficult for the UK projects to make much impact – unless they have some breakthrough technologies under test, of which there is no public evidence. Nevertheless, Government support for driverless vehicles might be justified if the impact on the transport system were clearly beneficial.

Transport benefits

Autonomous vehicles would need to be demonstrably safer than their human-driven counterparts to be publicly acceptable. This should be achievable, given that most crashes are caused by human error. So we may expect a safety benefit from driverless cars, and lower insurance costs. Beyond that, it seems likely that there will be two main impacts.

First, replacing the human driver with a robot would lessen the cost of licensed taxis and private hire vehicles, enhancing their competitiveness, which is why Uber is so keen on this technology. Such robotic vehicles would fill the present gap in service provision that exists between high-capacity, low cost public transport and low-capacity, high cost taxis.

Proponents of public transport are anxious lest demand for efficient high-occupancy buses  is reduced. On the other hand, the ready availability of robotic taxis would reduce the attractions of individually owned cars, and robotic shared-use minibuses would allow door-to-door conveyance at reasonable charges. So we can envisage a future in which the availability of shared-use autonomous vehicles fosters a shift away from private ownership in urban centres, with a beneficial impact on traffic congestion.

Second, private ownership is likely to remain popular in suburbs and beyond. Driverless cars will allow new options, for instance sending the vehicle home unoccupied, after delivering the occupant to their workplace, for use by others in the household. This could reduce car ownership per household, but would increase vehicle-miles travelled. Another option would be ‘parking on the move’ – programming your car to cruise round the block while you do your shopping. However, such unoccupied vehicles would add to traffic and worsen congestion in urban areas, so would need to be regulated, to give priority to occupied vehicles.

The main problem of the transport system is road traffic congestion. The test for any new technology is its likely impact on congestion. For autonomous vehicles, there are many possible impacts, both positive and negative. In the absence of evidence from deployment at scale, the outcome is uncertain. So the transport policy case for support for driverless vehicles remains unclear. Yet that lack of clarity justifies cautious support of development, testing and deployment, to understand better the implications of what could yet turn out to be an important innovation.

Traditional transport technologies based on mechanical and civil engineering develop quite slowly. In contrast, digital technologies are fast and disruptive. Autonomous vehicles are where the digital hare has to ride on the back of the mechanical tortoise, with as yet uncertain consequences for the speed of travel.

A version of this blog appeared in The Conversation on 21 November 2017.

 

 

The Mayor of London published a draft Transport Strategy in June. The consultation period has just finished. Generally, the draft is sensible in its intentions, emphasising the important aims of healthy streets and people, good public transport, and accommodating a growing population and economy.

One stated objective is to achieve 80% of all trips by walking, cycling or public transport by 2041. However, while reduction in the share of journeys by car is desirable, it would be very ambitious to achieve this aim.

Car mode share has been falling in London, from 50% of all trips (driver and passenger) in 1993 to 36% in 2015. I projected  that on existing policies it would fall to about 30% by 2040. This is happening because the capacity of the road network prevents traffic growth, and population growth therefore results in a decline of car mode share. However, a reduction to 20% car mode share of trips could be difficulty for the following reasons:

  • Walking in London has remained at 24% of all trips consistently for the past 20 years. Walking is the slowest mode, other than for very short journeys, and could therefore be difficult to increase.
  • Cycling is growing, but from a low base. However, it is difficult to get people out of cars onto bikes. Copenhagen has excellent cycling infrastructure and a strong tradition of cycle use, which comprises 30% of all trips. However, car use at 33% is not very different from London. Walking and public transport use are much lower than in London. Crowding on public transport is likely to be reduced by promoting cycling, but there may not be much impact on car use.
  • Growth of bus use will tend to be constrained by traffic congestion, and growth of rail use by crowding and the cost of investment in new routes.
  • Reducing carriageway available for cars, for instance by allocating more road space to pedestrians and to bus and cycle lanes, would tend to reduce car use, but would not reduce congestion and would be detrimental for goods deliveries.