9090thth Annual T.H.E. Annual T.H.E.ConferenceConference
Sign RetroreflectivitySign Retroreflectivity
Mike StaggsMike StaggsMobility & Safety Team LeaderMobility & Safety Team Leader
Federal Highway Admin. - IlinoisFederal Highway Admin. - Ilinois
OverviewOverview
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?What is Retroreflectivity?
“Reflective” is a generic term and is the reason we can see objects
Every surface is reflective!
Types of ReflectivityTypes of Reflectivity
Diffusereflector
Retro-reflector
Specularreflector
What Is a Retroreflector?What Is a Retroreflector?
Bead retroreflectivity– Light reflects off reflector
coat behind a small bead
Cube corner material– Light reflects off three sides
of prism
• Material that directs light back to the source
Sheeting Cross SectionSheeting Cross Section
(Type III – e.g. High Intensity)
Why is Geometry Important?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
Dimmer
More dim
Bright
Why Do We Install Signs?Why Do We Install Signs?
Guidance is MUTCD?
To help drivers
Yes
Engineering Decision?YES
!
Why?
Why is it Retroreflectivity Why is it Retroreflectivity Important?Important?
Critical for nighttime driving
Daytime - many cues available
Driver task relatively easy
Nighttime - few cues remain
Task more difficult
Crash Data: Non-DaylightCrash Data: Non-Daylight
0
10
20
30
40
50
Perc
ent
DistanceTraveled
FatalCrashes
Can we judge retroreflectivity Can we judge retroreflectivity during the day?during the day?
Problem: Retroreflectivity Problem: Retroreflectivity Degrades Over TimeDegrades Over Time
Visibility IssuesVisibility Issues
What do drivers see?
What do headlights do?
What is the vehicle impact?
Driver Luminance NeedsDriver Luminance Needs
048
121620242832
20 33 46 59 72 85
1x
32x
16x
8x4x2x
Starting at age 20, the amount of light needed to see an object the same way doubles every 13 years
Minimum Minimum RetroreflectivityRetroreflectivity
What is the concept?
Why is it important?
What has happened?
What are the recommendations?
When will it happen?
What is the Concept?What is the Concept?
Current specifications establish minimums for new materials
Devices must be visible to be effectiveIn-service minimum values will establish
the end-of-service life for devicesDevices not meeting in-service minimums
should be replaced
Current MUTCD Language 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 LegislationCongressional Legislation
for traffic signs and pavement markings which apply to all roads open to public travel.”
of Transportation shall revise the MUTCD to include a standard for a minimum level of retroreflectivity that must be maintained
1993 DOT Appropriations Act – “The Secretary
AASHTO Task ForceAASHTO Task Force
Created in November 1998Represents states, cities, counties,
academia, private industry, and FHWARecommendations received for signs in
December 2000
AASHTO ResolutionAASHTO Resolution
Desirable to assure adequate night visibility for signs
Regular assessments of retroreflectivity or planned replacements of signs “is necessary”
AASHTO RecommendationsAASHTO Recommendations
Minimum requirements should be simpleDo 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 methodsProvide 6 years to implement
AASHTO’s 4 Proposed AASHTO’s 4 Proposed Methods of Addressing Methods of Addressing
Retroreflectivity Retroreflectivity 1. Minimum sign retroreflectivity values
2. Minimum nighttime sign legibility distances
3. Nighttime visual sign inspection by calibration or sample
4. Maximum service life of signs
Research Recommended Minimum ValuesResearch Recommended Minimum Values
Sign Color Criteria
Sheeting Type (ASTM D4956-01a)
I II III VII VIII IX
White on Red CR ≥3 35 / 7
Black onOrange or
Yellow
BoldText ≥48” x 50
FineText <48” x 75
Black on White 50
White onGreen
Overhead x / 7 x / 15 x / 25 250 / 25
Shoulder x / 7 120 / 15
Sign MaterialsSign Materials
Engineering grade– ASTM Type I
Super engineering grade– ASTM Type II
High intensity– ASTM Type III
Microprismatic– ASTM Types IV, VII, VIII, IX
Roll-up– ASTM Type VI
Impact on Your Agency?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 & 5 Methods to Assess & Manage RetroreflectivityManage 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 & 5 Methods to Assess & Manage RetroreflectivityManage 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 & 5 Methods to Assess & Manage RetroreflectivityManage 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 & 5 Methods to Assess & Manage RetroreflectivityManage 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 & 5 Methods to Assess & Manage RetroreflectivityManage 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 & 5 Methods to Assess & Manage RetroreflectivityManage 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 RetroreflectometersSign Retroreflectometers
Impluse RM
Retrosign920 SE920
SMARTS Van
~$6,000 ~$8,000 ~$9,000
~$240,000
Questions?Questions?
http://safety.fhwa.dot.govhttp://safety.fhwa.dot.gov
