Transcript CALTRANS RETROREFLECTIVESIGN SHEETING

th
90
Annual T.H.E.
Conference
Sign Retroreflectivity
Mike Staggs
Mobility & Safety Team Leader
Federal Highway Admin. - Ilinois
Overview

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

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Retroreflectivity – What is it?
Materials - How do retroreflective materials
work?
Impact - Why is it important?
Visibility issues - How do the pieces fit
together?
Status of future requirements
What should be done now?
What is Retroreflectivity?
“Reflective” is a generic term and is the
reason we can see objects
 Every surface is reflective!

Types of Reflectivity
What Is a Retroreflector?
• Material that directs light back to the
source

Bead retroreflectivity
– Light reflects off reflector
coat behind a small bead

Cube corner material
– Light reflects off three sides
of prism
Sheeting Cross Section
Why is Geometry Important?

Light from source reflected back in a cone shape
 Retroreflectivity decreases as angles increase
 Intensity of reflected light decreases with distance from
cone axis
More dim
Dimmer
Bright
Why Do We Install Signs?
Why?
To help drivers
Engineering Decision?
YES!
Guidance is MUTCD?
Yes
Why is it Retroreflectivity
Important?
 Critical
for nighttime driving
Daytime - many cues available
Driver task relatively easy
Nighttime - few cues remain
Task more difficult
Crash Data: Non-Daylight
50
Percent
40
30
20
10
0
Distance
Traveled
Fatal
Crashes
Can we judge retroreflectivity
during the day?
Problem: Retroreflectivity
Degrades Over Time
Visibility Issues
What do drivers see?
What do headlights do?
What is the vehicle impact?
Driver Luminance Needs
Starting
at age 20, the amount of light needed
to see an object the same way doubles every 13
years
32
28
24
20
16
12
8
4
0
32x
16x
1x
2x
4x
20
33
46
8x
59
72
85
Minimum
Retroreflectivity
What is the concept?
Why is it important?
What has happened?
What are the recommendations?
When will it happen?
What is the Concept?

Current specifications establish minimums
for new materials
 Devices must be visible to be effective
 In-service minimum values will establish
the end-of-service life for devices
 Devices not meeting in-service minimums
should be replaced
Current MUTCD Language
2A.06: … basic requirements … uniformity
in design includes retroreflectivity… high
visibility by day and night
 2A.08: … shall be retroreflective … show
same shape and color day and night
 2A.22: should have adequate
retroreflectivity … should establish
schedule for inspecting (both day and night)

Congressional Legislation
1993 DOT Appropriations Act – “The Secretary
of Transportation shall
revise the MUTCD to
include a standard for
a minimum level of
retroreflectivity that
must be maintained
for traffic signs and
pavement markings
which apply to all roads open to public travel.”
AASHTO Task Force

Created in November 1998
 Represents states, cities, counties,
academia, private industry, and FHWA
 Recommendations received for signs in
December 2000
AASHTO Resolution

Desirable to assure adequate night visibility
for signs
 Regular assessments of retroreflectivity or
planned replacements of signs “is
necessary”
AASHTO Recommendations

Minimum requirements should be simple
 Do not publish numerical values in MUTCD
– Publish separately and reference in MUTCD

Need alternatives other than measured
retroreflectivity to assure adequate nighttime
visibility
 Agencies should choose from optional methods
 Provide 6 years to implement
AASHTO’s 4 Proposed
Methods of Addressing
Retroreflectivity
1.
2.
3.
4.
Minimum sign retroreflectivity values
Minimum nighttime sign legibility
distances
Nighttime visual sign inspection by
calibration or sample
Maximum service life of signs
Research Recommended Minimum Values
Sheeting Type (ASTM D4956-01a)
Sign Color
Criteria
I
White on Red
Black on
Orange or
Yellow
Black on White
II
CR ≥3
III
VII VIII IX
35 / 7
Bold
Text ≥48”
x
50
Fine
Text <48”
x
75

50
Overhead
x/7
Shoulder
x/7
White on
Green
x / 15
x / 25
120 / 15
250 / 25
Sign Materials

Engineering grade
– ASTM Type I
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Super engineering grade
– ASTM Type II
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High intensity
– ASTM Type III
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Microprismatic
– ASTM Types IV, VII, VIII, IX
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Roll-up
– ASTM Type VI
Impact on Your Agency?

What is our sign maintenance system now?
 Do we have a system that addresses
nighttime visibility of signs?
 What is the nighttime visibility condition of
our signs?
 What types of sheeting do we use now?
5 Methods to Assess &
Manage Retroreflectivity
1.
Visual Nighttime Inspection – the
retroreflectivity of an existing sign is
assessed by a trained sign inspector
conducting a visual inspection from a
moving vehicle during nighttime
conditions
5 Methods to Assess &
Manage Retroreflectivity
1.
Visual Nighttime Inspection – the
retroreflectivity of an existing sign is
assessed by a trained sign inspector
conducting a visual inspection from a
moving vehicle during nighttime
conditions
5 Methods to Assess &
Manage Retroreflectivity
2.
Measured Sign Retroreflectivity – sign
retroreflectivity is measured using a
retroreflectometer. Signs with
retroreflectivity below the minimum levels
need replacement.
5 Methods to Assess &
Manage Retroreflectivity
3.
Expected Sign Life – When signs are
installed, the installation date is labeled or
recorded so that the age of a sign is
known. Expected life based on
warranties, test deck measurements, or
actual measurements.
5 Methods to Assess &
Manage Retroreflectivity
4.
Blanket Replacement – All signs in an
area/corridor, or of a given type, are
replaced at specified intervals. This
eliminates the need to assess
retroreflectivity or to track life of
individual signs.
5 Methods to Assess &
Manage Retroreflectivity
5.
Control Signs – replacement of signs in
the field is based on the performance of a
sample of control signs. The control signs
may be a small sample located in a
maintenance yard or a sample of signs in
the field. The control signs are monitored
to determine the end of retroreflective life
for the associated signs.
Sign Retroreflectometers
920 ~$6,000
920 SE~$8,000
Impluse RM
Retrosign ~$9,000
SMARTS Van ~$240,000
Questions?
http://safety.fhwa.dot.gov