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Physical Mobility and Virtual Mobility

The impact on the roads of online activities: state of the research

"Where in the world do you want to go today?" ran the old Microsoft ad, in a simple statement indicating the boundless possibilities of virtual mobility. Online, you can work, shop, chat and do all kinds of things "in" (so to speak) places that would otherwise be well out of reach.

It seems self-evident that these kinds of online activities will have an impact on what we travel for, and how often we travel. There are limits, of course. Faced with a choice of going to the Maldives, or taking a virtual tour of the islands, the physical visit is far more attractive to most people.  Physical presence is always going to be the preferred, or necessary, choice for many activities. But increasingly online activity is preferred where

  • it takes the hassle out of travelling or distribution, and/or makes it more efficient
  • it opens up new opportunities for activity that otherwise would have been out of reach due to distance or cost.

"Virtual mobility", as the phrase implies, is not really mobility at all. It refers to undertaking activities that previously would have required transport to do. And in many cases, the activities undertaken are simulations of or substitutes for physical activities.

What all this adds up to is that online activities necessarily have both a spatial and temporal effect on our activities - we do what we do in different places than previously, and it takes a different amount of time to do it.

So how much does this make a difference on the roads?

Virtual mobility and flexible work

From the published research, the area where online activity is making a measurable difference is in the area of telework. There are many different kinds of telework, but two of the varieties have been the subject of more intensive investigation.  These are home-based teleworking, and working at local telecentres.

Here is a sample of findings from the research:

  • Teleworkers in the BT Workabout scheme reduced their travel 93 miles reduction per week for car users, 143 miles per week for rail users
  • Teleworkers at the Dutch Ministry of Transport made 17 per cent fewer trips and cut peak-hour car travel by 26 per cent. Household members also appeared to travel less than before
  • Teleworkers in the Greater Munich Area studied in the MOBINET project found that they reduced work trips by 43% and all trips by 19%
  • Users of the California Neighbourhood Telecenters Project demonstrated a 17% reduction in vehicle miles travelled per week
  • Users of Surrey County Council’s pilot telecentre reduced the length of their commute journey on average by 19%, and duration by 36%. Teleworking has now been introduced across the Council in the Surrey Workstyle programme.

These headline figures mask a variety of effects in terms of redistribution. The trips that do happen are often to different places, at different times and, within the household, often undertaken by different people.

It is worth noting that in most cases telework is not full-time. Across the teleworking population at large, it seems that around 1.5 days per week (6 days per month) is emerging as a typical figure. Although averages are higher at high tech or telecoms companies like BT, for most individuals a day and a half is a comfortable level. It remains to be seen whether this will change over time with improved technologies, greater familiarity and changes to management attitudes and workplace culture.

Looking at a wide range of studies, it is possible to generalise as follows:

  • average range 20-50 miles (person mile travelled) are saved per teleworking occasion
  • this leads to a typical range of savings of 1300-3500 miles per teleworker per year (given the incidence of teleworking in the studies at 1, 1.5 or 2 days per week).

It is pretty much established, then, at the individual and household levels, that there is a significant net traffic reduction from teleworking even when compensatory trips are taken into account.

Wider impact on the roads

A number of studies have attempted to aggregate these kind of findings to give a picture of the effects at city, regional or national level, and potential growth trends.

A kind of orthodoxy has been emerging, where rates of teleworking (numbers of days per week), average distances travelled and telework penetration rates (i.e. number of people teleworking/number of people who could telework) are combined to give an aggregate figure. However, this kind of approach contains many assumptions, particularly in the attempts to find how many people do or could telework. This is typically based on some kind of estimate about the numbers of "knowledge workers", or guesstimating the numbers of teleworkers as a subset of white-collar workers, and elaborating growth trends from the growth of the services sector.

One of the key assumptions in looking at potential ceilings in the number of teleworkers is the assumption that patterns of early adoption amongst mainly higher earning professional and managerial male workers are determinative of future trends. A paradoxical effect of such assumptions is that it may over-estimate the traffic reduction potential per teleworker (as higher earning men tend to commute longer distances) while under-estimating the total traffic reduction potential by not seeing the telework potential within lower paid and lower-skilled jobs.

In this kind of estimate, there is also often very dubious use of data that is collected for other purposes.  However, in some countries such as the UK and many other European countries, data is now collected in the Labour Force Survey (LFS) that provides a consistent if perhaps conservative way of measuring the numbers of people teleworking from home for at least one day per week.

Based on figures from the British LFS, on any day there are about 1.1 million people teleworking.  However, while this adds up to quite a high number of eliminated commute round-trip journeys, in percentage terms it currently makes only a small dent in total traffic figures. Growth in the number of teleworkers is also outstripped by both employment growth (there are far more new non-teleworkers than teleworkers in the workforce) and by total traffic growth for all purposes. It is also important to note that one telework occasion doesn't simply translate to one eliminated commute round-trip, as teleworkers may also "time-shift", i.e. shift their commute journey to a different time of day.

So there will need to be significant growth in teleworking, both in total numbers and the number of days each person teleworks, to begin to make a significant impact.

Rebound effects

There has been much debate about complementary or generative effects of telework and other online activities on transport. These tend to focus on:

  • Trip-chaining/multi-purpose trips: commuters often combine other activities with their commute journey, like shopping, school escort, etc. So when the commute trip is eliminated, a substitute trip for such purposes may still be needed.
  • Extra business trips: for teleworkers who visit clients, eliminating the commute trip and trips back to the office creates time for further trips to clients
  • Convenience of car at home – for teleworker and household: when the car is not used for commuting, it is up for grabs by the other household members for their use. Or if the teleworker is usually a public transport user, he/she may be tempted to use the car to, say, drive the kids to school
  • Relocation potential: a lot of literature assumes that teleworking will enable people to live further from their offices, and make fewer but longer journeys
  • Latent demand: other drivers occupy the roadspace vacated by teleworkers in congested areas.

A figure of around 50-60% "clawback" of travel savings through newly generated trips is often cited by commentators, largely on the basis of papers from a group of American researchers.

However, close inspection of the papers concerned shows that these figures are almost entirely speculative, however plausible the rebound effects might be. There are no measured studies as yet that demonstrate such effects. Some measured studies, on the contrary, indicate opposite trends, i.e. that households as a whole contract their "activity spaces" and their total travel when telework takes place. There is a lot more work to be done in this field.

A key question is "how far to cast the net when looking for rebound effects?"  The following diagram outlines one way to segment the various kinds of potential rebound effects from online activities:

At the moment research has only penetrated in to the first order rebound effects (rebound 1) and, in a few studies, into the second level in terms of some household effects. For level 3 and beyond there is an urgent need to capture new data and to develop new modelling techniques before any conclusions can be drawn.

For the column marked "Rebound X", there must be serious questions about the coherence of the speculation, as one becomes further removed from the original online activity in question, and other variables are involved - not to mention questions of causality.

For example, one study modelling the transport effects of e-commerce in the computer industry, while showing a net transport reduction, cancels these out by factoring in the following rebound effect. As online businesses are around 10% more efficient, it suggests, they can manage with around 10% fewer workers.  These workers are going to go out and do other jobs, hence create more traffic, etc.

Is this a legitimate rebound effect to factor in? At best, it is a complicated one, as it attributes their travel behaviour in one company as a rebound effect of their not working for another company! It also assumes that in their new situation that work arrangements do nothing to minimise their need to travel. At some point one needs to draw the line and say "This far and no further" in attributing rebound effects.

For individuals and companies, such rebound effects may be academic, someone else's problem.  The raw travel savings are sufficient incentive to change the way they work.

Transport effects from e-commerce and e-services

Research into the transport effects of e-commerce and e-services are very much in their infancy, as are the technologies and applications themselves. We will reserve more detailed discussion of these for a future article.  For the moment we can summarise the state of the research as for e-commerce follows:

  • General finding: delivery trips trips increase, in particular lights good vehicle deliveries, while personal shopping trips decrease. But studies tend to be based on speculative modelling, rather than observation.
  • There are major variations in estimates of reductions in shopping trips, depending whether researchers emphasise continuing need to buy other goods, or are optimistic about the range of goods that will become available and user uptake.
  • There are major variations in estimates about distribution trips, depending on weight given to potential increases in e-business efficiency and existing carries having the ability to absorb increases into existing delivery patterns
  • A few recent studies using life-cycle analysis for energy use in traditional versus online retail indicate a  similar total energy use, but energy consumption from transport reduces
  • Some expect e-commerce greatly to increase air freight, as consumers and industries source products from further afield. Bad for the global environment, but good news for surface transport policy, if local sourcing decreases??

For the impact from e-services there is an absence of research that deals with real numbers as opposed to theorising. But it is worth noting that the UK government is allocating £6 billion to developing e-government at all levels, and this is largely based on eliminating physical contact between bureaucracies and citizens - which implies a substantial transport reduction effect. One major difference between this and e-commerce is that at the end of the online transaction, much e-commerce still requires the distribution of a physical product, whereas e-government and other e-services mostly involve a "dematerialised" end-product.


We can summarise the state-of-the-art as follows:

  • Home-based and telecentre-based teleworking have a significant direct travel reduction effect, which is confirmed in empirical studies
  • The reduction effect endures when household activity is also measured
  • There are significant redistributive effects – destinations, time, mode and journey length
  • Other forms of teleworking are under-researched, but business case studies indicate significant travel savings for the organisations concerned
  • Research into the transport effects of e-commerce and e-services is at yet in its infancy
  • Most figures given for wider rebound effects are speculative
  • Transport studies tend to be weak on variations in technology and management in telework and e-commerce implementations, so studies do not necessarily compare like with like.

The upshot of this is that research does support the idea of using telework as a tool to reduce travel - but also that there is a lot more research that needs to be done before we see the full picture.

Further Information

This article is a timely updating of the earlier paper, Travel reduction and teleworking:
what we know 
and what we don't
(which we're keeping archived on the website for reference), and supplements the article Virtual Mobility - taking forward the UK research agenda.

This new article is based on further work by HOP Associates in 2002-3for the UK Department for Transport (DfT) and other transport agencies.

You can access summaries of most of the studies referred to at, the website for the DfT project.




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