Visual Performance for Motorists - Road Lighting: Fundamentals, Technology and Application - page 34

Fig. 3.21 Test situation at the
open-air road-lighting
laboratory. Driver's car
equipped with dipped
European beam

d remaining

d remaining

bright surrounds dark surrounds

Fig. 3.22 Remaining
distance, d remain , after the
reaction to the presence of
pedestrians positioned three
metres away from the border
of a traffic lane, as a function
of the average traffic-lane
luminance, L av . Uniformity,
U o > 0.4 and glare, TI < 10.
(Van Bommel and
Tekelenburg 1986 )

80

d remain
(m)

60

bright surrounds

40

car lights
only

20

dark surrounds

0

0.1

0.2 0.5

1

2 5
L av (cd/m 2 )

The importance of appropriate lighting for the surrounds of a road is confirmed
by the accident study referred to in the first chapter of this topic, in which the
authors reported that higher road-surface luminances result in lower accident ratios
(Hargroves and Scott 1979 ). Apart from the importance of a sufficiently-high road
surface luminance, they also reported that accident ratios were 20-30 % less on roads
falling in the group with surround luminances between 0.5 cd/m 2 and 1.2 cd/m 2 than
on roads in the group with surround luminances lower than 0.5 cd/m 2 .

3.5 Traffic Flow

Position-keeping in the traffic stream is another important safety aspect of the driving
task. Road lighting can also help in this respect. Night-time motorway driving tests
carried out over a distance of 50 km in a road simulator showed that motorists react
to the presence of a broken-truck on the emergency lane differently according to
whether there is lighting or no lighting. Figure 3.23 shows that on lighted motorways,
approaching motorists already started changing traffic lane some 360 m before the
breakdown, compared to a distance of only 130 m where there was no motorway