Standards and Recommendations - Road Lighting: Fundamentals, Technology and Application - page 105

9.3 North American Standard

9.3.1 Lighting for Roads with Motorized Traffic

The American National Standard Practice for Roadway and Street Lighting has been
revised by the Illuminating Engineering Society of North America (IESNA) and
is accepted by the American National Standards Institute (ANSI) in 2014 and is
published as RP-8-14 (ANSI/IES 2014 ). The Standard recommends the luminance
design method for straight roadways and streets, and the horizontal illuminance
design method for intersections and interchanges. For pedestrian areas, horizontal
and vertical illuminances are the recommended design parameters. As far as small-
target visibility (STV) is concerned the Standard Practice writes:

this method is still undergoing evaluation but may be a valuable tool when comparing the ex-
pected results of two designs delivering approximately the same luminance and illuminance
performance.

The criteria used for luminance and illuminance are largely the same as those of CIE,
with a few minor exceptions. For lighting level the criterion is L av as in CIE. For
uniformity, as in CIE, two criteria are used: the ratios L av /L min and L max /L min . The
ratio L av /L min serves the same purpose as CIE's U o value, being the reciprocal of
U 0 =

L min /L av . Note that the ratio L max /L min contrary to CIE's U l value, is not based
on a longitudinal line along the road but on the whole road area. For glare restriction,
as in the CIE, the combination of veiling luminance, L v , and average road-surface
luminance, L av , are used, but in a slightly different composition. RP-8-14 uses the
ratio L v /L av , which is called the veiling luminance ratio, whereas CIE uses TI, which
is 65 L v /L 0 . 8

av .
The road-lighting classes are—for roads not intended to have pedestrian or cyclist
activity—directly defined in terms of Freeways (class A and B) and Expressways.
The street-lighting classes for roads where pedestrians and cyclists are present are
termed Major roads, Collector roads and Local roads. Here a differentiation is made
between high, medium and low pedestrian activity. Table 9.9 shows, by way of
example, the recommended lighting values for Freeway class A, for Major roads and
for Local roads. The lighting level ranges from 1.2 to 0.3 cd/m 2 . The highest lighting
level specified is somewhat lower than the 2.0 cd/m 2 of CIE and EN.
The range of the uniformity ratio L av /L min goes from 3.0 to 6.0, corresponding
to CIE's U o values of 0.33 and 0.16 respectively. Since both CIE and EN require
U o values of 0.35 to 0.40, the American standard clearly specifies lower uniformity
values.
For glare, the range of the veiling luminance ratio of 0.3 to 0.4 corresponds to
TI values of 30 to 50. So the American standard permits of more glare than do CIE
and EN