Overview

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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

Engineering Decision?YES

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

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

121620242832

20 33 46 59 72 85

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

2. Measured Sign Retroreflectivity – sign retroreflectivity is measured using a retroreflectometer. Signs with retroreflectivity below the minimum levels need replacement.

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.

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. 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

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