1. travel

1
1*
Patricia L. Mokhtarian
If telecommunication is such a good
substitute for travel, why does congestion
continue to get worse?
Abstract: Saving travel has always been a motivation for the creation and use of information and communication technologies. So with the ongoing spread of ever-improving technologies, why do travel and congestion continue to increase? Twelve
reasons for this paradoxical result are presented, as well as four reasons why some substitution can be expected.
Keywords: complementarity, dematerialization, ICT, rebound effect, telecommuting, telework, transportation demand
management (TDM)
1. INTRODUCTION
Since the dawn of human history, people have devised means
of communicating at a distance (e.g., Crowley and Heyer,
2006). At first, we used sound (trumpets, bells, tom-tom
drums) or sight (signal flares on hilltops, flags on ships) to
exchange information efficiently. The development of tools
for written communication (hieroglyphs, alphabets, paper,
movable type) increased our ability to telecommunicate
many-fold, and the brief period of electronic communication
that we have experienced so far (radio, telegraph, land-line
telephone, television, fax, internet, mobile phone) has raised
that ability by several more orders of magnitude.
Saving travel has been at least an implicit motivation
for the creation of telecommunication technologies from
the beginning. By the time the telephone was invented in
the latter part of the 1800s, that motivation became explicit:
letters and articles appearing in the London Spectator and
The Times in 1879 speculated on the potential of the telephone to replace face-to-face meetings (Albertson, 1980;
de Sola Pool, 1979), and the science fiction of H. G. Wells
(“When the Sleeper Wakes”, 1899) and E. M. Forster (“The
Machine Stops”, 1909) imagined videoconferencing (or the
“kineto-tele-photograph”, as Wells put it) accomplishing
the same purpose. As far back as the 1960s (Owen, 1962),
researchers and planners began to explore the potential of
*Corresponding Author
Department of Civil & Environmental Engineering and Institute of
Transportation Studies, University of California, Davis, One Shields
Avenue, Davis, California 95616 USA, voice: 1-530-752-7062,
fax: 1-530-752-7872, e-mail: plmokhtarian@ucdavis.edu
1
telecommunications for reducing travel, and the energy crisis
of the 1970s prompted a number of additional studies (e.g.
Harkness, 1977). Thus, the modern hope that computers and
the networks to which they are connected could help alleviate
urban congestion is not particularly new. Surely, however, as
information and communications technology (ICT) has gotten cheaper, easier to use, more effective, and more widely
available in recent years, and as its use, therefore, has soared
— surely its impact on congestion must be quite powerful
by now?
This does not seem to be the case: travel by any measure
continues to increase in general, and metropolitan congestion in particular shows little sign of abating. In the United
States, for example, the average number of phone calls for
every man, woman and child rose 20% from 1984 (1,484
per year) to 2004 (1,781 per year) (Statistical Abstract of the
United States, 2008). Internet-using households comprised
some 70% of the population in 20041, up from a negligible
percentage in 1984, and mobile phone penetration shows
a similar trend2. Yet during roughly the same period, the
average annual miles driven per driver increased 34%, from
10,288 in 1983 to 13,785 in 2001 (Liss et al., 2005), and the
average annual hours of delay per traveler in the 437 urban
areas of the country increased 2.6-fold, from 14 in 1982 to 37
in 2004 (Schrank and Lomax, 2007).
What produces this paradoxical result? In the following
section, I present 12 explanations. The third section briefly
links the discussion to the literatures on rebound effects and
<http://www.internetworldstats.com/am/us.htm>, accessed July 22, 2008.
1
2
<http://files.ctia.org/pdf/CTIA_Semiannual_Wireless_Survey_YE2003.
pdf>, accessed July 22, 2008.
Transportation Letters: The International Journal of Transportation Research (2009) 1: (1-17)
DOI 10.3328/TL.2009.01.01.1-17
J. Ross Publishing, Inc. © 2009
2 Transportation Letters: The International Journal of Transportation Research
dematerialization. The fourth section offers four countervailing observations, supporting the expectation that ICT will
replace (some) travel. A fifth section concludes the paper.
Most of the principles presented here are not new — many
are at least 30 years old. The contribution of the paper lies to
some extent in the organization and exposition of those principles, and to a greater extent in the assembly of considerable empirical evidence to support what was, until relatively
recently, largely speculation.
2. WHY DOES ICT APPARENTLY NOT
REDUCE TRAVEL?
The twelve answers to the title question can be divided into
two groups: passive reasons versus active ones. The five passive reasons help explain why ICT does not always automatically substitute for travel, while the remaining seven describe
mechanisms by which ICT actively increases travel.
2.1 Not all activities have an ICT counterpart
Let us begin with the obvious, but often-neglected, basics.
Although technology is constantly pushing the envelope,
location still matters, in several ways. First, so far we still
need, or in some cases at least strongly prefer, the co-location
of human beings for certain types of activities. For example,
though surgical instruments can be manipulated remotely
(e.g. Morris, 2005), in most cases a cadre of medical staff
will still be on site to perform the surgery and care for the
patient. The robot has not yet been invented that will change
an infant’s diaper or comfort a child who has been hurt. Even
at a more mundane level, machines do not yet cut our hair.
Second, we need human workers in specific locations to perform activities involving specific objects. Examples include
gardening, cleaning house, repairing vehicles, and fixing
the plumbing. Third, we need material objects, rather than
digital files, for food, clothing, shelter, and amenities. Each
of these cases is an example of the “coupling constraints” of
Hagerstrand (1970), and in each instance, humans and/or
material objects need to be physically transported to specific
locations (Memmott, 1963) — an ICT alternative simply
does not exist. Although we can strive to reduce our demand
for physical objects and personal services, and to reduce the
travel required to meet minimal demands (through choosing
closer supplies and suppliers, as well as more efficient routing
and scheduling), and although ICTs such as mobile phones
can certainly loosen some coupling constraints (Dijst, forthcoming), we can never entirely eliminate these needs as long
as we are corporeal beings.
2.2 Even when an ICT alternative exists in
theory, it may not be practically feasible
It is also easy to overlook this transparent fact, but just
because technology exists does not mean it is always available
(an instance of Hagerstrand’s “capability constraints”). The
typical professional society meeting, for example, does not
have a teleconferencing alternative. Online grocery shopping
is still not offered in many areas, and has been discontinued
in others (Murphy, 2007)3. Broadband internet access is
not (yet) ubiquitous. For that matter, in some places (“cold
spots”?) neither is telephone service, whether landline or
mobile.
Several scholars have commented on the physical equipment required to maintain virtual connectivity. At the system level, even wireless networks require control hubs and
transmission towers, and at the individual level, the presence
of an ICT network does a person little good if the battery
dies or the hard drive crashes. There are also place-based
societal (rather than technological) restrictions on the use of
ICT (Hagerstrand’s “authority constraints”), as when mobile
phone use is prohibited in theaters, or while using some
means of transport. And finally, some feasibility constraints
are due to the lack of knowledge or the economic means to
access ICT equipment or services (e.g. Schwanen and Kwan,
2008).
2.3 Even when feasible, ICT is not always a
desirable substitute
The point that ICT is not always an acceptable replacement for “being there” is another issue readily neglected
by technological enthusiasts, but ordinary people are well
aware of it. A conference fulfills many functions beyond the
straightforward exchange of information made possible by
teleconferencing (assuming it were available): it signals the
importance of the meeting to the participants; it may take
place in a high-amenity location, it may enable side trips or
activities such as visiting friends or other desirable places, it
constitutes an escape from the routine or pressures of work
and home, it may be a symbol of status, and it facilitates
interpersonal relationships both within and outside the
confines of the minimally-necessary information exchange
(Aguilera, 2008).
Similar arguments can be made about other putative
substitutes for travel (Day, 1973). Commuting to a conventional workplace potentially fulfills a number of functions
For a recent list of services and locations serviced, see <http://mashable.
com/2008/06/05/online-grocery-shopping/>, accessed July 18, 2008.
3
If telecommunication is such a good substitute for travel, why does congestion continue to get worse? 3
that telecommuting cannot readily replicate: access to an
activity-rich work vicinity, serendipitous social encounters,
visibility to upper management, tangible trappings of status
(a nice office, a secretary), and escape from domestic pressures, among others. A number of researchers (e.g. Kraut,
et al., 2002a) have commented on the value of face-to-face
interaction in a work context, even in the Information Age.
One recent analysis (Torre, 2008) points to the role of ICT
in fostering collaborative work among distant colleagues,
but argues that at least “temporary geographical proximity”
(involving episodic face-to-face encounters) is still essential.
Given that it is “[t]he mobility of individuals, which makes it
possible to implement this mechanism” (p. 870), the implication is one of more travel rather than less. Similarly, Urry
(2004 and elsewhere) eloquently argues for the importance to
social interactions of occasional physical copresence requiring travel, echoing a point of view expressed as early as 1977
(Albertson).
In the same vein, store shopping can serve a number of needs beyond the purely functional (Tauber, 1972;
Mokhtarian, 2004). It affords opportunities for social interaction with friends, store personnel, and casual passersby
(Chung, 2002). Entertainment/leisure activities may be bundled at the same shopping location (such as the multiplex cinema in the shopping mall; the coffee shop in the bookstore;
or the aquarium, theme park, and racecar track in the Mall of
America; see, e.g., Kaufman, 1995 and www.mallofamerica.
com), and for some people, the activity of shopping itself is a
form of leisure or entertainment (Salomon and Koppelman,
1988). Mall-walking as a type of deliberate exercise is common in the U.S., particularly among seniors, and even if one
does not systematically “take four laps around the mall” as
many do, the mere act of shopping can be a welcome form of
physical activity. In some cases it is a deliberate break from a
long stretch of being sedentary (e.g. shopping on one’s lunch
hour during the workday) or isolated (Gould and Golob,
1997), or reflects the need for escape or simply for a change
of scenery.
2.4 Travel carries a positive utility
As hinted in the preceding section, one reason why ICT is
not always a desirable substitute for travel is that travel can
be valued for its own sake — i.e. the motivation to travel can
be intrinsic or “autotelic”, in psychological parlance (e.g.,
Csikszentmihalyi, 1990), as opposed to extrinsic or instrumental to achieving some other end. This is another principle
that is often overlooked by transportation specialists (who are
taught that the demand for travel is derived from the demand
for spatially separated activities), but which is at least instinctively understood by “regular people”. Adventure-seeking,
conquest, variety-seeking, independence, control, status,
exposure to the environment, information-gathering, curiosity, escape, exercise, mental therapy, scenery, synergy, and
the need for a transition zone are among the reasons people
travel, or travel more than they must (e.g. by choosing longer
routes, or more distant destinations, for a trip that needs to
be made anyway).
Collectively, these motivations are readily accepted in
the case of leisure activities (many of which — hiking, sailing,
skiing, and so on — are themselves travel; Borgers et al., 1989;
Elias and Dunning, 1986; Landers and Arent, 2001; Tinsley
and Eldredge, 1995), as well as tourism (Nicolau, 2008),
exploration (Anderson, 1970; Pasternak, 2003) and migration
(IOM, 2005). A number of scholars suggest that they apply
— to some extent — in the context of everyday urban travel
and long-distance business travel as well (e.g. Albertson,
1977; Couclelis, 2000; Metz, 2004; Mokhtarian and Salomon,
2001; and the special double issue of Transportation Research
Part A on the positive utility of travel, Vol. 39, Nos. 2 & 3).
Of course, the derived demand paradigm is still quite useful,
and it seems likely that the increment of daily travel that can
be attributed purely to these autotelic needs is relatively small
(though perhaps not negligible). But it also seems likely that
much of our “derived” travel is fulfilling a dual role: getting
us to desired destinations, while simultaneously satisfying
our need to travel for its own sake. This observation not only
applies to short-term travel choices, but extends backwards
in time to our medium-term choices of activity types and
locations, and to our longer-term choices of residential and
job locations (Handy et al., 2005) — all of which may, consciously or unconsciously, take into account a fundamental
need to travel for its own sake. To the extent the autotelic role
is in play, individuals will be much less inclined to adopt ICT
substitutes for travel.
Consider commuting, the trip purpose considered most
important in the standard hierarchy of mandatory, maintenance, and leisure purposes (Reichman, 1976). A number
of scholars (e.g. Ory et al., 2004; Redmond and Mokhtarian,
2001; Richter, 1990; Salomon, 1985) have pointed out the
benefits of commuting (though some of those benefits relate
to activities conducted while traveling rather than the travel
itself, as discussed further in Section 2.9), and the popular
press apparently has no trouble finding ordinary commuters
to corroborate those effects (see references within the works
already cited). In an empirical study of telecommuting,
Mokhtarian and Salomon (1997) identified an attitudinal
factor they called “commute benefit”, and found that high
scores on that factor significantly reduced the preference to
telecommute. And as suggested in Section 2.3, one can similarly attribute some of the aforementioned positive qualities
of travel to shopping trips, a “maintenance” trip purpose
4 Transportation Letters: The International Journal of Transportation Research
which is also considered more or less obligatory under the
derived demand paradigm.
2.5 Not all uses of ICT constitute a
replacement of travel
Understanding that the ICT version of an activity is not
always a good substitute helps us to realize that in many
cases, the ICT version is undertaken not as an alternative to
traveling to the activity, but as an alternative to not conducting the activity at all. In those cases, ICT augments the set of
activities conducted, but does not (directly) replace any.
In some situations, that means that ICT is assumed to
be a “second-best” way of participating in the activity, when
the “first-best” way of being there in person is not possible
or practical. For example, distance learning is a growing
segment of the education market, and can be (though is not
always) an effective means of conveying knowledge (Bernard
and Abrami, 2004). Few would argue, however, that it is just
as good as being on a campus and in a classroom, but rather
that the latter option offers a far richer social and pedagogical
experience. On the other hand, the alternative for many if not
most distance learners is not to travel to a campus and sit in a
classroom, but rather to forgo the education altogether. That
is, distance learning extends an educational opportunity to
those who could not otherwise take part, because of distance,
cost, time, or other constraints. Similar comments have been
made about the ability of teleconferencing to make it possible
for people to attend a meeting who otherwise could not have
(e.g. Albertson, 1977). Although social exclusion is a legitimate concern, the internet is enriching the lives of countless
people who have serious mobility limitations, by increasing
at least the virtual accessibility of people and places (e.g.
Kenyon, et al., 2002). And ICT is allowing new patterns
of quasi-continuous “connected presence” to develop, in
which frequent text messages and other telecommunications
between family members or close friends emphasizes their
presence-within-absence (Licoppe and Smoreda, 2005).
In other situations (including, perhaps, some of the
examples just offered), the in-person version of the activity
may not even be considered “first-best”, or desirable. Hilty
(2008, p. 42) perceptively comments,
“Can working at home ever be functionally equivalent to working at the office? We think that people
do telework not because telepresence is functionally
equivalent to, but because it is different from, physical
presence! We think that virtual substitutes for physical processes will never be functionally equivalent
to the physical processes, but will always have some
advantages and disadvantages as compared with
physical processes. To ask for functional equivalence
is misleading, because it denies the different quality of
the virtual alternative.”
Some portion of internet shopping constitutes purchases
on impulse, or of specialized items not available locally. In
those cases, the consumer may not have wished that the
items were available in local stores instead, but rather is
content with ordering exactly what she wants online. If the
online option did not exist, the consumer would not have
gone to the store to seek an item she did not even know she
would be buying, or which she had reason to think would
not be there.
Similarly, considering the ease of broadcasting and
forwarding, probably most e-mail messages would not have
been sent by another means — certainly not by face-to-face
communication — if e-mail did not exist. This observation
is consistent with the unique character of e-mail (compared to other forms of ICT) found in several studies (e.g.
Meenakshisundaram and Mokhtarian, 1999; Dijst, forthcoming).
Overall, it seems that ICT is indeed growing more rapidly
than travel, and is likely to continue to do so (Mokhtarian,
2003). To date, however, it does not follow that travel is
actually declining, whether measured on a per capita or total
basis. It has simply been growing more slowly than ICT. As
discussed further in Section 4.3, however, this historical relationship could be altered, in favor of more substitution, by
the rising costs of travel.
Figure 1 schematically illustrates the discussion so far.
The first three reasons (together with the fourth, as a special
case of the third) successively filter the set of all place-based
activities, eliminating activities that are either impossible,
difficult, or not preferable to conduct via ICT. Conversely,
the fifth reason filters out ICT-based activities that are either
impossible, difficult, or not preferable to conduct via travel.
(We could have had a symmetric figure, successively distinguishing the subsets of ICT activities that have no travel
counterpart, that may nominally have such a counterpart
but for which travel is not feasible in every circumstance,
and for which travel is feasible but not desirable. But from
the standpoint of the desired effect of reducing travel, it is
more important to make those distinctions among activities
involving travel). The remaining intersection, consisting of
activities for which an individual is able and willing to replace
travel by ICT, is at least conceptually relatively small.
We now turn to the seven ways in which ICT actively
stimulates more travel. The first four reasons in this group
belong together: in all cases the question is, what happens
when ICT frees time and/or money by eliminating or altering some activities? Section 2.6 considers the general case,
replaced by ICT
ICT not desirable
ICT not feasible
no ICT
counterpart
If telecommunication is such a good substitute for travel, why does congestion continue to get worse? 5
ICT
activities
that don’t
replace
travel
activities conducted
via travel
activities conducted
via ICT
Figure 1. Schematic relationship among activities involving travel and those involving ICT
while Sections 2.7 - 2.9 treat some idiosyncratic aspects of the
special case in which travel itself is the activity being altered.
Section 2.7 deals with saving money on travel. With respect
to freeing travel time, Section 2.8 takes the system-level
perspective, in which ICT is used to improve the efficiency
of the transportation network, whereas Section 2.9 reflects
the individual’s use of ICT while traveling. Thus, these four
sections deal with short-term indirect mechanisms: first ICT
affects a given activity, which then has travel-stimulating
consequences. Section 2.10 makes the case for ICT directly
stimulating travel, through several means. And Sections 2.11
and 2.12 describe longer-term, more systemic impacts of ICT
that result in greater travel.
2.6 ICT saves time and/or money for other
activities
In general, ICT has enabled some activities (such as paying
bills, accessing and distributing information, performing
mathematical calculations) to be conducted faster, and has
(at least in some circumstances) altogether eliminated some
activities (such as individually calling or mailing physical
documents to every member of a group). The elimination of
travel through the use of ICT to perform the activity is also
included here (i.e., the familiar examples of “tele-substitution”, such as telecommuting, teleconferencing, teleshopping, distance learning, telemedicine, and so on — when
those applications actually do remove or at least shorten
a trip, which, as discussed in Section 2.5, is not always the
case).
By eliminating or speeding up some activities, ICT
saves time for other activities — some of which may involve
travel, and some of which may be travel. Thus, for example,
one of the early concerns raised about telecommuting (e.g.
Mokhtarian, 1991) was that the saved commute time might
be used to make other trips. However, with respect to telecommuting in particular, this effect has not been empirically
observed to any appreciable extent (Mokhtarian, 1998). Many
telecommuters appear to be “travel-saturated” from the days
on which they still commute, and tend not to travel much
at all on telecommuting days. In other cases, trips made on
telecommuting days are simply shifted from other times, e.g.
from the weekend to a work day. When new trips are generated by telecommuters, they tend to be shorter, off-peak, and
sometimes by benign modes such as walking or bicycling, so
that the net impact of teleworking is still positive.
On the other hand, the potential trip generation impacts
of other forms of tele-substitution have been less well-studied.
It seems likely, for example, that some of the time and money
saved by teleconferencing for routine meetings is permitting
other trips, for creating or solidifying new business relationships, or to more interesting places — trips that otherwise
would have been crowded out by the demands of routine
business travel. Similarly, money saved by finding bargains
online may be spent on more consumer goods, involving
transportation in their manufacture, distribution, and acquisition (Mokhtarian, 2004; Williams and Tagami, 2002). Such
6 Transportation Letters: The International Journal of Transportation Research
effects may be difficult to capture with typical cross-sectional
self-reported behavioral data, since the connection between
time/money saved and new trips being generated may not be
perceived by the average survey respondent.
While the primary focus of this paper is on personal
activity, this effect (among others) has a counterpart for
physical goods. For example, Milgrom and Roberts (1990)
and Milgrom et al. (1991) describe the role of ICT in increasing the efficiency of manufacturing and inventory systems,
thereby lowering costs, and hence supporting the production
of more goods, which require more transportation. (We discuss a similar role in logistics systems under Section 2.8).
2.7 ICT permits travel to be sold more
cheaply
When the activity affected by ICT is travel itself, money can
be saved not just by the elimination of the travel activity altogether, but also when the unit price of travel is lowered. For
both business and leisure purposes, the internet and other
ICTs have revolutionized travel marketing (e.g. Buhalis and
Licata, 2002). The ability to save money by comparing prices,
receiving price alerts, and making last-minute purchases of
trips can increase travel through several different means.
First, it could simply reduce the cost of a trip that was going
to be made anyway, and just as in the case of saving time
described above, some of that savings could be spent on
more travel. Second, it could allow the substitution of a more
distant destination for a closer one: with a fixed monetary
budget, if one can now go to Brazil instead of Boston, why
not? (some would ask). And third, it could stimulate entirely
new trips to be made, as more trips fall within the discretionary spending means of more people (this variation could also
be classified under the direct stimulation of travel, discussed
in Section 2.10).
2.8 ICT increases the efficiency of the
transportation system, making travel more
attractive
ICT has impacts not just at a personal level, but at a system
level as well. One such impact could be the increased speed
resulting from a drop in demand if non-negligible amounts
of telecommunications substitution were achieved. Speeds
can also be increased through ICT applications to system
management and control. Either way, when the (time and/or
money) cost of travel is lowered, economic theory indicates
that the demand for it will rise.
The role of ICT in improving the efficiency of the transportation network is many-faceted, and well-established.
The telegraph not only initially followed railroad rights-of-
way, it quickly became essential for system control (Spar,
2001). Increasingly today, various Intelligent Transportation
System applications such as in-vehicle navigation systems
with real-time traffic information, electronic toll collection,
signal timing, highway ramp metering, and so on act to speed
travel, and/or to accommodate higher volumes of travel
without decreasing speeds (e.g. Bekiaris and Nakanishi,
2004). Over the long term, the dream is of sophisticated
collision-avoidance and other technologies that will permit
platooning of vehicles at high speeds (e.g. Parent, 2004).
The congestion-improvement goals of such applications are laudable, but if history is any guide, increasing the
speed of travel (whether through making more efficient use
of existing capacity, or adding new capacity) does not ultimately reduce trips or improve congestion. In the near term,
Downs (2004, pp. 82-86) points to the phenomenon of “triple
convergence”, in which newly-available capacity prompts
travelers to shift time, route, and/or mode so as to take
advantage of the higher speeds, while in the long run, new
travel demand is generated by the improved accessibility of
spatially-dispersed locations (e.g. Zahavi and Talvitie, 1980;
Schafer and Victor, 2000; also see Gwilliam and Geerlings,
1994).
On the freight side, similar mechanisms are at work. The
cost and time of goods movement is being reduced through
Electronic Data Interchange (EDI), Global Positioning
System (GPS), Radio Frequency Identification (RFID), and
other ICT-based technologies and services (e.g. McFarlane
and Sheffi, 2003; Mukhopadhyay et al., 1995) — which lowers the price of goods, which increases their demand, which
increases the demand for transporting the raw ingredients
and finished products (e.g. Hilty et al., 2006; Milgrom and
Roberts, 1990; Milgrom et al., 1991).
2.9 Personal ICT use can increase the
productivity and/or enjoyment of travel time
Section 2.4 spoke of the positive utility of travel itself. In
addition to the utility of reaching a desired destination — the
conventional derived demand view of travel — Mokhtarian
and Salomon (2001) refer to one more component of the
“tripartite nature of the utility of travel”: the utility of activities conducted while traveling. It has always been possible
to conduct activities while traveling (talking to companions,
looking at scenery, and, if not operating the vehicle, reading,
sleeping, and so on), and the potential of such activities for
increasing the utility of travel has been acknowledged — even
if not emphasized — in the transportation literature for several decades (e.g., de Serpa, 1973). However, ICT broadens
the scope of available options (commonly including speaking
on the phone, sending text messages, working on a laptop,
If telecommunication is such a good substitute for travel, why does congestion continue to get worse? 7
browsing the internet, watching videos, and playing electronic games).
Accordingly, recently a number of scholars have begun to
speak of time spent traveling in positive, rather than its conventionally negative, terms. Lyons and Urry (2005) comment
on the potential productivity and even ultra-productivity of
time spent traveling, particularly in the context of ICT usage.
Jain and Lyons (2008) point out that travel time can be a gift
as well as a burden. Peters (2006, p. 1) notes that “travel not
only takes time, … it also makes time” (emphasis original).
By making travel time more enjoyable and/or productive, ICT at a minimum reduces the motivation to save travel
time (e.g. by teleworking, or moving one’s residence), and
at the margin may actively increase it (Lyons et al., 2007). A
benign example of the latter effect occurs when one chooses a
longer public transport commute over a shorter auto trip, in
part because of the ability to work on the bus or train. A less
benign example (from the standpoint of attempts to reduce
travel) occurs when a professional can make more business
trips because of the increased ability to remain connected to
other clients and the main office while “on the road”.
Thus, several researchers have counted the utility of
activities conducted while traveling (as well as the utility of
travel itself) among the possible explanations for observed
increases (or, in some cases, stability) in per capita travel
time (e.g. Littlejohn and Joly, 2007; Metz, 2008; van Wee et
al., 2006). Others (Ettema and Verschuren, 2007) have found
that, all else equal, those who listen to music while commuting value their travel time at a lower level than others (which,
as they point out, may reflect the self-selection of a group of
travelers who value comfort over time, but that merely supports the point).
2.10 ICT directly stimulates additional travel
The mechanisms discussed so far have all operated either
through negation (ICT is not an option at all, or is not available in this context, or is not a suitable substitute, or does
not actually replace a trip), or through a chain of effects (ICT
reduces the time and/or money cost of some activities, and
some of the savings are spent on more travel). One of the
most important mechanisms, however, may be the positive
and direct role of ICT in stimulating additional travel. This
mechanism can work in at least three different ways.
First, the content of a telecommunicated message may
directly invite travel. In some analyses we may focus too
much on the travel behavior of the messenger, and fail to
take into account the content of the message. To be sure, the
military trumpets or church bells of old may have spared
some messengers from having to deliver information in
person, but the messages themselves said, “assemble for
battle!”, or “come to the church — something important is
about to happen!” The irony has not been lost on the student
of communications history, that one of the first reported
telephone messages consisted of Alexander Graham Bell saying “Mr. Watson, come here; I want to see you” — thereby
generating a trip, even if only down the hallway to the next
room4. Today, mobile telephony facilitates impromptu rendezvous (Licoppe, 2008) and “flash mobs” (Srivastava, 2005).
Whether or not cost savings occur (as discussed in Section
2.7), the sheer volume of internet-based travel marketing can
generate new trips. And in the near future, location-based
marketing (e.g. Ngai and Gunasekaran, 2007) will generate
numerous side trips to nearby stores.
Second, by increasing accessibility to people, places,
activities, events, information, and goods and services, ICT
increases the engagement in activities that involve collateral
travel, at least in some cases. This is something of a sequel to
the principle of Section 2.5: ICT makes an activity available
to people who otherwise wouldn’t have engaged in the activity at all — but now we add the observation that such activities often have some travel associated with them. Consider an
early videoconference demonstration, which involved traveling to two locations with a video link between them, instead
of to a single central site where the monthly meeting would
normally have been held. The evaluation found that although
per-capita distance traveled was lower for the videoconference, so many more people attended the meeting that total
distance traveled was greater than for a typical meeting at
the central location (Mokhtarian, 1988). Of course, a novelty
effect could partly account for the higher attendance, but so
also could the greater convenience of only having to travel a
short distance.
Similarly, consider a government report, or other document. Formerly, thousands of such documents would be
physically printed and mailed. Now, a much smaller number
is printed at the source, but by posting the document to the
internet and/or e-mailing it widely, it is readily available to
millions who would not otherwise have known of its existence (or bothered to request it). Only a fraction of those millions will print the document, but that fraction might be large
enough to exceed the former number of copies. Delivery of
thousands of finished documents through postal services has
been replaced by delivery of many times that amount of paper
and toner to distributed locations (Mokhtarian, 2004).
For a third example, consider telemedicine, particularly
its use to provide diagnostic services to remote populations.
Because more people will use such a service, and more often,
than would travel to be diagnosed in person, more condi4
E.g., <http://www.loc.gov/exhibits/treasures/trr002.html,> accessed July
18, 2008.
8 Transportation Letters: The International Journal of Transportation Research
tions may be discovered than would otherwise have been the
case — which may then require travel to an urban medical
facility for treatment. For a fourth example: online dating
services expand one’s set of social contacts, and some faceto-face meetings inevitably result.
Other instances abound. Maps may now be considered
a relatively low-tech ICT, but centuries ago, they were revolutionary. Several authors have commented on their power
for stimulating travel, both for commerce (Spar, 2001) and
for tourism (Perrottet, 2002). Today, the convenience of
GPS-based navigation systems may embolden timid explorers to make numerous more forays into the unknown than
would otherwise have been the case. Down through the ages,
travel writing (and its graphic relatives — art, photography,
and motion pictures) has stimulated countless readers/viewers to follow in the footsteps of the writer/artist. Today, the
internet multiplies and intensifies the reach of that genre of
communication.
Couclelis (2000) adds another dimension to these first
two types of direct effects. She observes (pp. 5-8) that,
beyond the “explosion of the size of the contact sets of individuals and firms,” ICT has enabled an increasing fragmentation of activities in space and time. She hypothesizes that
that fragmentation, involving the “interweaving and mutual
dependence of physical mobility and electronic communication, not merely the spreading use of ICTs”, “is one of the
reasons for the widely observed increases in travel demand
in the industrialized world.”
Third, by making communication essentially instantaneous, ICT fosters the expectation of rapid gratification. On
the consumer side, some authors have observed that e-shopping is often accompanied by the demand for fastest-possible
shipping, with air freight being far more energy-intensive
than slower shipment by truck or rail (Matthews et al., 2001;
Murtishaw and Schipper, 2001). On the goods movement
side, it has been noted that the just-in-time (JIT) supply
chain principle made possible by ICT can lead to more frequent deliveries at less-than-truckload (LTL) capacities, and/
or the increased reliance on energy-intensive and superiorservice modes (Hesse, 2002; Holmes, 2001).
All of the reasons presented to this point can be considered short term, in that they can act more or less immediately, at the individual level. In the long term, however,
individual effects aggregate up to the system level, feedback
occurs, and new processes evolve (in contrast to merely new
ways of conducting old processes). The effects of this longterm evolution can also be difficult to identify, particularly
if one is looking for a straightforward replacement of “this”
place-based activity with “that” ICT alternative. But those
effects could be profound. In the remainder of this section,
we mention two long-term reasons why ICT may stimulate
travel.
2.11 ICT is an engine driving the increasing
globalization of commerce
The critical role played by ICT in the increasing globalization
of commerce is virtually undisputed. Equally incontrovertible, a key (and inevitable) effect of globalization has been
to create new travel (both passenger and freight), as ever
more widespread and interconnected business relationships
are developed. As a historical but prototypical example,
a number of scholars have commented on the synergistic
relationship between the telegraph and railroads. Among
them, DuBoff (1980, p. 478) succinctly captures the nature of
the telegraph’s contribution. He notes that not only did the
telegraph lower information and transaction costs, a direct
stimulant to business in its own right, but that these reductions constitute
“resources released for alternative uses: the direct
benefits of the telegraph were distributed to the rest of
the economy through decreased costs of coordination
and movement, higher real incomes, and widened
areas of economic activity… For firms, everything
pointed to the growing feasibility of higher sales volumes through penetration of hitherto distant markets
… The size of any market … is limited by the costs of
obtaining information, negotiating exchanges, and
moving goods. Historically, these cost constraints
have been loosened by technology and especially by
breakthroughs in communication and transportation.”
Similarly, Albertson (1977, p. 40) comments that “[t]he
opening of the transatlantic cable … resulted in an enormous
increase in both telecommunications traffic and travel across
the Atlantic”. Today, telephony, the internet, and other ICTs
(see Section 2.8) are operating in much the same way: both
as a direct stimulus to the development of new markets (for
everything from raw materials to finished products to services), and with a multiplier effect as cost savings are redeployed to further support commerce (essentially the effects
of Sections 2.10 and 2.6 — 2.9, respectively, interacting over
time and aggregating up).
Globalization clearly generates increased telecommunication. As Aguilera (2008) notes, at first glance that may not
require greater physical movement (of goods and people)
to follow (after all, many business activities are carried out
through ICT), but the principles described in preceding
sections serve to explain why in fact it does. As a result of
those principles, executives and sales staff travel ever far-
If telecommunication is such a good substitute for travel, why does congestion continue to get worse? 9
ther and more frequently to develop new clients and serve
existing ones, employees are exchanged among global sites
to enhance knowledge transfer and travel to professional
meetings all over the world, inter-firm collaborations and
geographically dispersed project teams have increased over
time, cheaper labor and raw materials make it cost-effective
to transport them from farther away, and the worldwide customer base created through internet-based marketing as well
as more conventional channels generates greater travel in
the transport of finished products to the consumer (see, e.g.,
Aguilera, 2008; Berkhout and Hertin, 2004; Boudreau et al.,
1998; Frandberg and Vilhelmson, 2003; Harvey et al., 2000;
Jones, 2004). Higher fuel prices have started to reshape some
of these patterns (e.g. Rohter, 2008), but will not reverse
them completely.
2.12 ICT facilitates shifts to more
decentralized and lower-density land
use patterns
At the metropolitan scale, ICT has also weakened (though
by no means eradicated) the agglomeration economies that
once kept cities more compact (e.g. Audirac, 2005). Because
physical proximity is a less binding constraint than it once
was, one natural outcome is increased diffusion of firms and
residents to locations where land or labor is cheaper or amenities are higher. Lower densities, in turn, are well-known
to be associated with greater distances traveled (e.g., van de
Coevering and Schwanen, 2006).
The effect of ICT on land use patterns, however, is quite
complex. For one thing, ICT not only facilitates decentralization, it also facilitates concentration into more energy- and
travel-efficient land use patterns (e.g. de Sola Pool, 1980).
Thus, it is important to keep in mind that technology is
itself neutral, and can be applied in ways both positive and
negative. We do have a personal and collective choice in the
matter (Gottman, 1983). For another thing, decentralization
has many causes, and the post-World-War-II acceleration
of pre-existing trends in that direction certainly predates the
advent of the internet and other modern ICTs. Thus, it is
quite difficult, and possibly futile, to attempt to determine
the proper amount of “blame” to allocate to ICT for current
decentralization patterns. Nevertheless, it seems reasonable
that some portion of the responsibility does belong there.
The case of telecommuting and residential location helps
illustrate the causal complexities. Telecommuters do tend to
live farther from work than average (Mokhtarian et al., 2004):
did the ability to telecommute motivate them to do so, or is
telecommuting a solution to the longer commute they chose
to take on for other reasons? One study of State of California
workers found that the preponderance of evidence favored
the latter explanation (Ory and Mokhtarian, 2006), and that
in any case people telecommuted frequently enough that, on
average, their total commute distance did not exceed that
of the comparison non-telecommuters (Mokhtarian et al.,
2004). Nevertheless, additional study is needed in this area.
3. Ties to other literatures
It is relevant to situate the preceding discussion within the
general topic of rebound effects, about which a sizable literature exists (see, e.g., the special double issue of Energy
Policy, Vol. 28, Nos. 6 & 7, 2000). The term is perhaps most
often applied to a case in which a consumer good becomes
more energy efficient, but where the resulting energy savings
in turn stimulates additional energy consumption, thereby
reducing (or, in the “backfire” effect, even more than counteracting) the savings. The mechanisms by which this happens have been classified into three categories (e.g. Berkhout
et al., 2000; Hertwich, 2005):
•
•
•
direct: The lower per-unit cost of operating the
appliance directly stimulates greater use of it (an
“own-price effect”), leading to higher energy consumption for the same or less money compared to
before. For example, more efficient air conditioners
may motivate consumers to leave them on longer and/or put the thermostat on a cooler setting,
achieving greater comfort at the same or lower
price. Similarly, improvements in automotive fuel
economy have been accompanied by increases in
distance traveled (Small and van Dender, 2007).
Thus, as Hilty (2008) points out, merely increasing
efficiency is not a sufficient condition for reduction
in resource consumption.
indirect: The money saved by operating the more
energy-efficient appliance is spent on other goods or
activities, which consume energy.
dynamic, macro-scale, structural: In the longer
term, lower energy prices lead not only to greater
demand for the existing ways of consuming energy,
but also generally promote economic growth and
stimulate new activities which were not financially attractive before, and which in turn consume
energy.
These three mechanisms can be at least loosely applied to
the effects of ICT on travel, where instead of a specific more
energy-efficient appliance, we mean a generally more energy(or cost- or time-) efficient way of conducting activities (i.e.
via ICT). The indirect mechanism corresponds reasonably
well to the reasons of Sections 2.6 — 2.9, and the macro-scale
10 Transportation Letters: The International Journal of Transportation Research
mechanism to the reasons of Sections 2.11 and 2.12. The
correspondence of the direct mechanism to Section 2.10 also
works, not in the sense that ICT use directly generates more
ICT (though that is one mechanism at work in the observation of Section 2.5), but in the sense that the more efficient
ICT-based way of conducting activities directly leads to more
activities (involving travel) being conducted. (For a different
application of these three categories to the environmental
impacts of ICTs, see Berkhout and Hertin, 2004. Also see the
very useful Figure 7-1 of Hilty, 2008).
The literature on dematerialization is also pertinent to
this discussion. Many authors have noted the general trend
toward physical objects becoming smaller and/or lighter, and
in some cases (e.g. recorded music) virtually disappearing
altogether (which is sometimes referred to as immaterialization). But physical shrinkage at a unit level is sometimes
accompanied by a greater multiplication of units, with the
result that more resources are consumed overall (the “miniaturization paradox”, Hilty, 2008). For example, television sets
have become less material-intensive, but at the same time,
households now own several of them (including larger and
larger models) where they used to own just one (Bernardini
and Galli, 1993). Even as mobile phones have gotten smaller,
the increase in subscribers has more than compensated for
the per-unit decrease in materials required (Hilty, 2008).
With respect to goods movement, improvements in fuel efficiency have been counteracted by the move to less efficient
modes (e.g. from rail to trucking) and to increases in overall
activity levels (Murtishaw and Schipper, 2001). These effects
are similar to the second mechanism described in Section
2.10. And Marvin (1997) uses many of the arguments presented in Section 2 to question the “dematerialisation of
cities”.
4. IS THERE ANY HOPE FOR A
SUBSTITUTION EFFECT?
Given the relationships outlined above, is there any hope
whatsoever then, that ICT can reduce travel? In this section,
we discuss four reasons for optimism.
4.1 Sometimes, ICT does directly substitute
for making a trip
Probably most of us can furnish personal examples in which
ICT did, in fact, replace travel. In the US, the telegraph did
close down the Pony Express (Standage, 1998). The volume
of single-piece first-class mail and periodicals sent through
the US Postal Service has been declining for several years,
due to “electronic diversion of bills and statements, alternate
payment methods, … the absence of new hardcopy applications”, and increasing reliance “on the Internet as a substitute
for hardcopy publication of news, information, and entertainment” (<http://www.usps.com/strategicplanning/cs07/
chpt2_005.htm>, accessed July 17, 2008). Teleworking also
appears to be an example in which the net impact is one of
(modest) travel reduction (Choo et al., 2005). Several recent
studies of the relationships between communications and
travel, while generally finding complementarity effects to
dominate (Choo and Mokhtarian, 2007), have also found a
number of statistically insignificant effects, suggesting that
impacts in both directions are largely balancing each other
out (Choo et al., 2007; Lee and Mokhtarian, 2008; PonsNovell and Marsal, 2006). So substitution effects might, in
fact, be substantial, even if often more-than-counteracted by
generation effects.
4.2 ICT consumes time (and/or money) that
might otherwise have been spent traveling
Although Section 2.9 focused on ICT as an overlay to traveling, and indeed many ICT activities are conducted in a
multi-tasking mode, some of them do prevent other activities
from taking place. To reverse the Peters quote in that section,
ICT not only makes time (through eliminating or speeding
up some activities, and making formerly unproductive travel
or waiting time more pleasant or productive), it also takes
time — a phenomenon referred to in the time use literature
as “displacement”. So, for example, a small panel study of
young people (18-23 years old) conducted by Vilhelmson
and Thulin (2006) found that increases in in-home ICT use
seemed to displace time spent on out-of-home activities and
travel. A similar displacement effect was deduced from crosssectional data by Nie et al. (2002), though in that case there
is possibly a self-selection effect at work (less sociable people
are likely to spend both more time on the internet, and less
time socializing; it is their personality causing both effects
rather than a direct displacement effect of the internet). In
contrast, at least one larger longitudinal study (Kraut et al.,
2002b) found that initial negative effects of the internet on
social life diminished over time.
Figure 2 illustrates one possible typology of impacts of
ICT on activities. Category 1 is the “straightforward” substitution of traveling to an activity with conducting it by
ICT — the subject of Section 4.1, and the choice occurring
in the innermost intersection of Figure 2. Category 2 is the
indirect effect just described — the converse counterpart to
If telecommunication is such a good substitute for travel, why does congestion continue to get worse? 11
direct (own-activity)
substitution: activity X is
now done by ICTs instead
of the traditional way
activity generation or
modification: activity X
either would not have
oc-curred without ICT, or
is materially changed by it
1. Choice between ICTbased v. traditional
activity (replacement; e.g.
ICTs are the Mokhtarian and Salomon,
1996)
end – the
basis of
2. Generation of new
conducting
ICT activities (time
the new
displacement – ICTs
activity itself
taketime from other
activities; e.g. Nie et al.,
2002; Vilhelmson and
Thulin, 2006)
4. ICTs as enabler/
facilitator/modifier of
activities (e.g. Srinivasan
and Raghavender, 2006)
3. ICT-enabled
reallocation of resources
to other activities (ICTs
give time or money that
permits other activities to
occur; e.g. Ferrell, 2004)
ICTs are
the means
(of saving
time,
money);
can affect
non-ICT as
well as ICT
activities
cross-activity substitution:
activity(ies) X affect(s) activity(ies) Y
Source: Salomon and Mokhtarian (2008), adapted from Mokhtarian et al. (2006).
Figure 2. Types of ICT impacts on activities
the mechanism of Section 2.6, which is Category 3. Category
4 includes the direct stimulation effect discussed in Section
2.10.
4.3 When travel becomes more costly,
difficult, or dangerous, ICT substitution will
increase
Generalizations drawn from empirical research are inevitably based on a “business as usual” assumption. That is,
workplaces are functional and safe, the transportation system
is operating normally and safely, and the price of travel is
perceived to be “affordable”. When any of those conditions
change, the substitution of travel by ICT inevitably becomes
more attractive. The scholarly and/or popular media have
reported promotion of and/or increases in telecommuting
and/or teleconferencing in response to fires (Pratt, 1991a)
and floods (Bates, 1992) making workplaces unsafe; regional
or local events such as blizzards5, hurricanes6, earthquakes7,
transit strikes8, and other incidents affecting transportation
system operations9; fears for safety at the workplace or while
traveling, e.g. from terrorist attacks10 or the occasional freeway sniper11; planned extreme events such as the Olympics12;
and currently, of course, in response to dramatically increased
gasoline prices13.
5
<http://findarticles.com/p/articles/mi_m0EKF/is_n2099_v42/ai_17817161>,
accessed July 21, 2008.
6
<http://www.washingtonpost.com/wp-dyn/content/article/2005/09/13/
AR2005091301973.html>, accessed July 21, 2008.
For the October 17, 1989 Loma Prieta (Northern California) earthquake, see
Pratt (1991b). For the January 17, 1994 Northridge (Southern California)
earthquake, see, e.g., <http://query.nytimes.com/gst/fullpage.html?res=9
407E1DB1338F930A25751C0A962958260>, accessed July 21, 2008, and
Wesemann, et al. (1996).
7
<http://www.internetnews.com/infra/article.php/3572256>, accessed July 21,
2008.
8
9
<http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2007/05/06/
BUG73PKP9G1.DTL&type=printable>, accessed July 21, 2008.
See the Congressional testimony titled “Telecommuting: A 21st Century
Solution to Traffic Jams and Terrorism”, given July 18, 2006, at <bulk.
resource.org/gpo.gov/hearings/109h/34546.pdf>, accessed July 21, 2008.
Also see <http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2001/10/28/
AW159330.DTL&type=printable>, accessed July 21, 2008, regarding
increases in telecommuting immediately following September 11, 2001.
10
For example, the Washington “Beltway sniper” of 2002; see <http://www.
worldnetdaily.com/news/article.asp?ARTICLE_ID=29298>, accessed
October 2, 2008.
11
Regarding the 1984 Los Angeles Summer Olympics, see <http://www.calmis.
ca.gov/file/occguide-archive/telework.htm>; regarding the 1996 Atlanta
Summer Olympics, see <http://govinfo.library.unt.edu/npr/library/
news/275e.html>; regarding the 2002 Salt Lake City Winter Olympics,
see <http://www.tfhrc.gov/pubrds/janfeb02/olympics.htm>; all accessed
July 21, 2008.
12
13
<http://www.whsv.com/home/headlines/25514464.html>, accessed July 17,
2008.
12 Transportation Letters: The International Journal of Transportation Research
These and other examples demonstrate that under
emergency conditions a great deal of work, commerce, and
personal interaction can still take place through the power of
ICT. What happens after the system returns to normal, however? One disaggregate study of the 1989 San Francisco Bay
Area earthquake found considerable persistence of telecommuting several months later (Pratt, 1991b), while one aggregate study of the 1994 Los Angeles-area earthquake found
little impact of telecommuting even during the immediate
aftermath, and traffic patterns reverting to pre-event levels
within a few months (Wesemann et al., 1996)14. A sustained
rise in the price of gasoline, however, defies history and could
produce a different result. On the other hand, I suspect that
the relationships described earlier in this paper are rather
robust, and that human nature is fundamentally opposed to
limiting travel very much, for the reasons already indicated.
In either case, it is extraordinarily useful to have an effective
alternative to travel in place, whether as a short-term contingency measure or a long-term mitigation strategy.
4.4 ICT can be deployed to make shared
means of transportation more attractive
ICT enables pre-trip and en-route information about public transport (and perhaps ridesharing) to be more readily
available, which can help lower key barriers to increasing
ridership: lack of information about the service in general,
and uncertainty with respect to a trip in progress (Kenyon
and Lyons, 2003). Further, as indicated in Section 2.9, the
ability to use ICT to “buy back” some or all of one’s travel
time can lower the disutility of traveling. To the extent that
public transport service providers can facilitate ICT usage
on their system (e.g. Wi-Fi-enabled train cars and stations,
and reliable mobile phone reception throughout the system,
if mobile phone use can be sequestered in a way to prevent
annoying other passengers), and market it as a competitive
advantage over driving, the more appealing collective modes
of travel can be.
5. CONCLUDING REMARKS
Although the preceding section gives some causes for hope,
in reality the challenges are great. It is difficult to improve
technologies and services for the purposes of reducing travel,
without having those same technologies and services used
to stimulate travel via the mechanisms described in Section
2. For these reasons, we should keep a balanced view of the
paradoxical role of ICT in addressing transportation needs:
part of the solution, to be sure, but — for the same reasons —
an inescapable part of the “problem” as well (Hilty, 2008).
The extent to which ICT’s stimulation of travel is in fact
a problem could be considered debatable. Certainly, reducing the negative externalities of travel is an important public
goal. But it is also true that mobility has considerable personal, social, and economic benefits, and as a society we will
pay a certain price for curtailing mobility. Perhaps it can be
agreed, however, that providing more alternatives to travel —
increasing people’s freedom to choose non-travel alternatives
— is a good thing, and so is using the transportation system
more efficiently so that more travel can be accommodated
within the existing infrastructure. ICT has a clear role to play
in both of these strategies, and public policies can be developed to support both.
ACKNOWLEDGEMENTS
A much shorter version of this paper, titled “i-Mobiliteit”,
initially appeared in the Dutch-language periodical Agora in
Fall, 2007 (pp. 15-18). A revised version of similar length was
presented at the First Indo-US Symposium on Advances in
Mass Transit and Travel Behaviour Research (MTTBR-08),
February 12—15, 2008, in Guwahati, India. It will appear in
Verma and Pendyala (2008) under the title, “The impacts
of telecommunications technologies on travel behavior:
Thoughts on the Indian context.” Conversations with Xinyu
(Jason) Cao, Helen Couclelis, and Gil Tal have helped clarify
some of the ideas presented in this version.
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