ROAD SIGNING
RESEARCH
A study of Road signing
angularity in London
1.0 INTRODUCTION
1.1
Background
The Traffic Control Products Group of 3M UK plc,
commissioned The MVA Consultancy to study the entrance
angularity of traffic signs on the London Primary Route
Network. The research covered:
■ Angled viewing conditions for motorists.
■ The performance of a range of retro-reflective sign face
sheetings.
The work was undertaken by a team led by Peter Guest
(an Associate of The MVA Consultancy) and Ken Huddart
(an Adviser to The MVA Consultancy and formerly Chief
Traffic Engineer, Greater London Council).
Entrance Angle
Note: Technically, two entrance
angles can be calculated per
car; one from each headlight.
1.2
Objectives
■ To assess the incidence of angularity in different road
configurations on the London Primary Route Network as
a whole.
■ To carry out an analysis of the entrance angles of signs
installed in typical London signing locations. This
included a sample of signs installed on the Highways
Agency’s own trial site on the A4, West London.
■ To quantify any additional driver benefits resulting
from the use of superior retro-reflective materials
(3M™ Scotchlite™ VIP Diamond Grade Reflective Sheeting,
or High Intensity (Class 1), rather than a limited angularity
Class 1A product of the type defined in the DoT’s
Technical Advice Note, TA/19/81).
1.3
DoT sign performance requirements
DoT regulations require that reflective materials used in the
manufacture of traffic signs must comply with BS873 part 6:
1983. Reference is also sometimes made to TA/19/81, the
forerunner of the British Standard, which refers to limited
angularity reflective materials. Photometric performance is
measured in terms of the coefficient of retro-reflectivity under
various entrance and observation angles.
1.4
Terminology
■ Normal: A line running at 900 to the sign face.
■ Incident light: the light causing the sign to reflect - usually,
a vehicle headlight.
■ Entrance angle: the angle between the normal, and the
incident light.
■ Observation angle: the angle between the observer’s eyeline and the source of the light subtended at the sign face.
Good performance at high observation angles is
particularly important for commercial vehicle drivers, for
example, who are positioned well above the headlights;
it is also important in urban locations where visibility is
required at short range.
■ First Look distance: a distance calculated by allowing six
metres from the sign, for every one centimetre in the
x-height of the sign lettering.
■ Last Look distance: defined in TA/19/81 as 5.7S, where S
is the sign displacement from the vehicle path. This relates
to a maximum recommended viewing angle of 100,
(see diagram over).
ROAD SIGNING
RESEARCH
2.0 METHODOLOGY
2.1
Development of measurement technique
Key measurements were taken for each sign from the
viewpoint of the motorist and used to determine which
locations would benefit from sign materials with enhanced
angularity such as Scotchlite™ VIP Diamond Grade sheeting.
The measurements included:
■ The sign offset distance. This is the perpendicular distance
from the centre of the sign to the vehicle path and was
measured for all appropriate traffic lanes at each location.
■ The entrance angle at the first look distance. If the sign
was obscured at the first look point, the angle was
calculated at the distance the sign could first be seen.
■ The entrance angle for each traffic lane at the last look
distance.
2.2
Survey sample
Most of the 65 sign locations chosen for analysis were on the
A4 or the A406 and they included a wide variety of signs. The
sample, representative of typical sign locations on the London
Primary Route Network, included:
■ Grade and grade separated junctions.
■ High speed roads.
■ Minor and major side roads.
■ Roundabouts and signalised junctions.
The sample also included the Vauxhall Cross area so that
the sample could include sign positions commonly encountered
at inner London gyratories. The combined sample sites were
sufficient to assess the angularity requirements of signs on all
types of roads other than motorways.
■ The distance from the driver back from the sign which is
subtended by an entrance angle of 150, for each traffic
lane.
Adjustable
protractor
Black contrast
cardboard
■ First and last look distances for motorists viewing signs as
they exit or orbit roundabouts.
Sighting element –
white
Sighting element –
black upper half,
white bottom half.
Measuring Instrument
2.3
Last Look distance as defined by DoT in TA/19/81
Drivers viewing angle is approximately 10O
The measuring instrument
A specially made portable angle-measuring device was created
which included a large protractor with an adjustable arm and
two sighting elements; the instrument was held against the
centre face of the sign and adjusted until the sighting elements
fell in line with the driver’s line-of-sight. The angle could then
be read.
Summary of last look entrance angle
by road category
Road category
2.4
Total
Signs
<= 15°
Last look entrance angle
16° to 30° 31° to 45° 46°+
Retro-reflective sheeting performance
1. Straight
46
38
8
-
-
■ Class 1A: Sheeting which does not meet a Class 1
specification due to a limited retro-reflective performance
at wide angles.
2. Junction
12
11
1
-
-
3. Roundabout
15
5
3
4
3
Total
73
54
12
4
3
Class 1A sheetings, therefore, only meet the retro-reflective
values shown in Table 1A of DoT Technical Advise note
TA/19/81 (forerunner to the British Standard).
■ Class 1: Sheeting which meets retro-reflective performance
values shown in Table 1, British Standard 873: part 6: 1983.
■ 3M™ Scotchlite™ VIP Diamond Grade sheeting: This is up
to three times brighter than Class 1 sheeting and has
excellent performance at wide entrance and observation
angles.
Junction characteristics on the
Primary Route Network
Junction Type
% of
Junctions
First look angle (%)
0 < 15°
15°+
Total
Roundabout
22
39
61
100
Other
78
85
15
100
3.0 SUMMARY OF MVA FINDINGS
Summary of first look entrance angle
by road category
Road category
Total
Signs
First look entrance angle
<= 15°
16° to 30° 31° to 45°
46°+
4.0 CONCLUSIONS
1. Straight
46
39
7
-
-
2. Junction
12
10
1
1
-
3. Roundabout
15
4
6
2
3
Total
73
53
14
3
3
It was estimated that a fifth of the signs on the London
Primary Route Network would benefit from the use of retro
reflective materials which performed well at entrance angles
above 150.
Over 60% of all paths measured at roundabouts had first look
positions greater than 150. At the last look points on
ROAD SIGNING
RESEARCH
roundabouts nearly 55% of signs had entrance angles greater
than 150, and 30% of signs had entrance angles greater
than 300.
73% of roundabout nose signs had entrance angles greater
than 150.
Grade separated junctions were likely to have roundabouts
with numerous road signs - 23% of signs need to perform at
high angles. For a significant number of junctions it would
be necessary to use a higher performance material, such as
3M™ Scotchlite™ VIP Diamond Grade sheeting, in order to
allow drivers to see the sign.
For acute entry angles, the requirements of TA/19/81 are
satisfied by VIP Diamond Grade, Class 1, and Class 1A
materials - but if VIP Diamond Grade is used the last look
position will be extended well beyond the requirements of the
DoT. Where the first look position is obstructed (by a tree, for
example) the extended last look could allow the driver
adequate time to read and act on the sign. This benefit is even
more important at critical locations, such as roundabouts,
where most signs appear to be seen after the point that would
be the last look position at most other sites.
The ability to view a sign with entrance angles exceeding 150
typically increases a driver’s viewing time by up to 4.5 seconds
at 30 mph.
The benefits of using high performance materials at night
were significant and have been reinforced by a separate
MVA study (Road Signing Research: A Study of Driver
Perception); this showed that drivers could read signs
made with 3M™ Scotchlite™ VIP Diamond Grade sheeting
sooner than signs made of Class 1 or Class 1A materials.
Summary copies of this report are available from
3M Traffic Control Products on 01344 858697.
Produced in liaison with:
Traffic Control Products
3M United Kingdom PLC
3M House, PO Box 1, Market Place,
Bracknell, Berkshire RG12 1JU
Tel (01344) 858697
Fax (01344) 858479
The MVA Consultancy
MVA House
Victoria Way, Woking
Surrey GU21 1DD
Tel (01483) 728051
Fax (01483) 755207
© 3M United Kingdom PLC 1996.
ArtHaus 6/96/5T
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