Purpose and Benefits of Road Lighting - Road Lighting: Fundamentals, Technology and Application - page 3

Studies in many countries and by many different institutions have shown that road
lighting can help to reduce the number of night-time accidents by more than 30 %
(CIE 1993 ; Elvik 1995 ; Elvik et al. 2009 ; Wanvik 2009 ). At some 60 %, the reduc-
tion of fatal accidents and of accidents involving serious injury is even greater. An
analysis of the accident database containing all fatal accidents in the USA on both
urban and rural roads, showed that of the various types of fatal accident, the type
involving pedestrians increases most under conditions of low lighting level (Sullivan
and Flannagan 2007 ). Thus, those traffic roads with many pedestrians seem to benefit
most from good road lighting.
Recently, a direct link has been established between visual performance obtained
from different road lighting installations at intersections in Minnesota (USA) and the
reduction in traffic accidents at night (Rea 2012 ; Bullough and Rea 2011 ) . Where
the so-called relative visual performance (RVP— see Sect. 3.3.3) increases from less
than 0.7 to between 0.8 and 0.9, the percentage of traffic accidents is reduced by ap-
proximately 15 %. A long time ago, in the UK, detailed lighting measurements of 100
different urban road sections (speed limit 50 km/h), each with a minimum length of
1 km, were linked with the night/daytime accident ratios, which were recorded over a
3 year period on the same road sections (Hargroves and Scott 1979 ). There where the
average lighting level on the road surface (one of the parameters that positively in-
fluence visual performance) was higher, the night/daytime accident ratio was lower.
Roads with an average luminance level in the category 1.2-2 cd/m 2 showed 20-30 %
lower accident ratios than roads in the category 0.3-1.2 cd/m 2 . Gibbons and Lutke-
vitch ( 2014 ) collected the accident rates from seven US States, over a 5 year period.
With a mobile laboratory, They made in-situ illuminance measurements on stretches
of road where accidents occurred. The accident rates will subsequently be corre-
lated with the lighting level. Preliminary results show a significant decrease in the
night/daytime accident ratio with increasing road-lighting level. Visual performance
does, indeed, directly affect traffic safety.
Sometimes it is suggested that the presence of road lighting encourages motorists
to drive faster. Even if this were to be the case, it does not change the fact that
road lighting reduces accidents. It would mean that the above-mentioned accident-
reduction figures would have been even greater had there been no such increase in
speed. Research into a possible speed-increasing effect of road lighting however
shows that the effect is limited to some 1-3 km/h (Folles et al. 1999 ; Assum et al.
1999 ; Hogema et al. 2005 ) or that it is non-existent (Remande 2009 ).
Road lighting can increase the capacity of a motorway during the hours of dark-
ness. This could be of practical benefit in those countries where, during the winter, the
traffic peaks after sunset or before sunrise. Van Goeverden et al. ( 1998 ) showed that
the capacity increase, expressed in “passenger car equivalents/hour”, on a two-lane
motorway amounts to 2.5 %, and on a three lane motorway to 1.7 %.
In built-up and residential areas the lighting should serve not only the visual
performance of motorists but also that of slow-moving traffic participants, such as
pedestrians, cyclists and moped riders. The lighting should enable them to orientate
themselves in the environment and to follow their path without the risk of stumbling,
colliding with or falling over potentially dangerous obstacles or hazards.