Context
Humans are strange creatures: give them a safer
car and they drive less safely. Well that's one of
the messages from research into driver behaviour.
Leonard Evans (1994, p.282) writes:
The question of road users responding
to changes in the safety of traffic systems has
also long been recognised.
In a paper written more than half a century ago
entitled 'A theoretical field-analysis of
automobile driving,' Gibson and crooks [1938,
p. 458] write:
More efficient brakes on an automobile
will not in themselves make driving the automobile
any safer. Better brakes will reduce the absolute
size of the minimum stopping zone, it is true, but
the driver soon learns this new zone and, since it
is his field-zone ratio which remains constant, he
allows only the same relative margin between field
and zone as before.
An explanation for this lies in risk homeostasis
theory (RHT). RHT arguses that people have a
desired or target level of risk; they feel right
taking a certain amount of risk and adjust their
behaviour if they perceive they are exposed to more
or less risk. Another term for this is behavioural
adaptation - adapting behaviour to a change in
circumstances.
In Target Risk, Gerald Wilde (1994,
pp. 109-114) uses RHT theory to explain the results
of research into the behaviour of Munich taxicab
drivers. In this study part of a taxi fleet in
Munich was equipped with ABS. The drivers knew of
the advantages offered by ABS and drove vehicles
that were in all other ways the same as others in
the fleet. Over a period of several years, these
drivers were
- over represented in crashes where they were
at fault
- more often recorded as braking extremely
hard
- made sharper turns in curves
- were less accurate in their lane-holding
behaviour
- proceeded at a shorter forward sight
distance
- made poorly adjusted merging manoeuvres
- created more traffic conflicts
- drove faster
- had more accidents under slippery driving
conditions
Studies in the US by Hertz (1996) and in Canada
by Grant and Smiley (1993) revealed results similar
to those above.
Road safety experts express varying opinions as
to the reasons for ABS not reducing the frequency
of crashes. Regardless, there seems cause for
concern and caution.
An OECD scientific expert group's response to
the Munich study was this:
Behavioural adaptation of road users which may
occur following the introduction of safety measures
in the transport system are of particular concern
to road authorities, regulatory bodies and motor
vehicle manufacturers, particularly in cases where
such adoptions may decrease the expected safety
benefit.
Some driver training experts argue the reason
the safety benefits of ABS are not realised is that
drivers are not taught how to use the braking
system correctly. They say some drivers release
brake pressure when they feel the pedal shudder
(the effect of ABS being activated), and they lack
the knowledge and skill to use the system
properly.
What can we learn from this?
- Those who manage organisations should not
assume that a direct safety benefit will result
from safety initiatives.
- Where active safety features are added to
vehicles it may be better that drivers do not
know about them.
- Where technology or features such as ABS are
introduced into fleets, drivers should
participate in a familiarisation programs.
- Familiarisation programs should attend to
the psychological dimensions of behaviour
adaptation and provide participants with
strategies to monitor and manage their risk
taking behaviour.
Read a plain English explanation of how
risk
homeostasis theory can be used to describe
risk-taking behaviour and how you can use it to
change people's driving behaviour.
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