IEEE Technology and Society Magazine - June 2019 - 37

vehicles on congestion, vehicle kilometers traveled (VKT), and travel
demand. These strongly related concepts may help to understand that it is
impossible to change one factor without causing an effect on the other.
In his article, Wiseman seems to
undervalue these interactions.

quality high-capacity transit [5]. The
ing level could be set in order to disincrease in VKT may result from selfsipate induced demand [10].
parking trips, empty trips, or new
Traveling always involves costs
demand from individuals unable to
and externalities, no matter the
drive or who shifted away from pubtransport mode used. Roads can be
lic transportation [6].
seen as a common good integrated
Driverless cars can motivate
in a shared-resource system. Indiempty car trips, for example, before
viduals acting according to their own
picking up and after dropping off passengers, or while
waiting to be called. Increasing driver convenience may
encourage passengers to
Wiseman adopts a biased
choose longer commute and
perspective without considering
errand trips, and more distantly sprawled households
or analyzing the interaction
[7]. If no regulation or charging policy is implemented,
between technological,
VKT will certainly increase,
sociological, and policy issues.
since it will be cheaper for a
car to drive around than to
pay parking fees [8]. If VKT
self-interest will use the maximum
increases dramatically, the idylavailable road capacity in order to
lic scenario of reduced congestion
meet their own goals. This behavior
and of additional free space due
is contrary to the common good of
to less parking cars would be an
all other individuals since it will drain
illusion. Similarly, emissions per
that resource availability. AdditionVKT may decrease, but emissions
ally, individuals tend to underprice
throughout the day may actually
their trips [11] and the lower cost
increase. Environmental impacts are
of an autonomous vehicle trip may
related to per-kilometer emissions
even aggravate this problem. Thereand therefore will be dependent on
fore, it is important to price road
the degree to which driverless cars
usage and parking spaces correctly,
employ more fuel-efficient and less
and to include externalities such as
polluting technologies [5], [9].
greenhouse gas emissions, congesImpact on Demand
tion pricing, or VKT taxes. Such reguWidespread adoption of driverless
latory policies are not popular since
cars may have the same effect as
they would increase the cost of ownadding lanes to the roads or highing and using a car. Unfortunately,
ways. Such an increase in road
without popular support, political
capacity could decrease the internal
support is very difficult to obtain.
price of the car travel, which in turn
Only the collective awareness of citicould increase the demand. Particuzens would allow the implementalarly during peak periods, the potention of these type of measures.
tial paradox of autonomous driving
In order to minimize the negameans that even if road capacity
tive impacts caused by increased
increases, average delay may not
VKT and induced demand, which
decrease substantially. Therefore, the
would mitigate the positive effects
challenge is how to keep demand at
of driverless cars, there is also the
manageable levels. Congestion pricneed to promote attractive alternaing may be the answer and the prictives. High-capacity transportation

Impact on Congestion
Reduction in vehicle crashes, increased autonomous driving efficiency,
enhanced vehicle throughput, and
increased car and ride sharing are
key factors affecting congestion in
a scenario where driverless cars
take the lead. At a first glance, driverless cars can remove a significant number of vehicles from the
roads. The impact may be particularly important if car ownership
declines and ride sharing increases.
Martinez et al. [5] present a simulation considering a fleet of shared
and single occupant driverless cars.
This fleet does not consider additional travel demand (it should
deliver the same trips as today in
terms of origin, destination, and
timing) and it should replace all car
and bus trips. The authors concluded that a shared driverless car, combined with high-capacity public transport (train or metro) would need
65% fewer vehicles during peak
hours. In this simulation, a single
occupant driverless car without public transport would still remove 23%
of the cars used today at peak hours.
However, the study does not
take into account any new demand
that could be induced by increased
capacity. Hence, impact on congestion will only be significant if the
movement and storage of vehicles is
priced correctly.

Impact on VKT
Most modeling relating to the impact of driverless cars indicates an
increase in VKT, even in scenarios
assuming the availability of highJUNE 2019

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IEEE TECHNOLOGY AND SOCIETY MAGAZINE

IEEE Technology and Society Magazine - June 2019

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