Reflective Traffic Signs
Reflective Warning Signs
To meet new FHWA guidelines, older Engineer Grade signs are being cycled out for more visible Diamond Grade signs (though the deadline for the change has been extended due to the expenses involved).
Optimum placement of reflective traffic signs
Retroreflective signs are illuminated for the human eye when the entrance angle..

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The science behind reflective traffic signs
What are reflective traffic signs and what is their importance? Elaborate on how these

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New requirements of Federal Highway Administration (FHWA)

On May 14, 2012, the FWHA published the final revisions to the Manual on Uniform Traffic Control Devices (MUTCD). The manual defines criteria "used by road managers nationwide to install and maintain traffic control devices" on public roads.

Recently, however, the Obama administration suspended the 2018 deadline for mandatory sign replacement initiated under the Bush administration primarily because of the cost to municipalities.

Safety improvements

The Manual on Uniform Traffic Control Devices recommendations for current safety improvements for municipalities include the following mandatory guidelines in the latest edition of the Manual:

    Section 2A.06 – Design of Signs: The basic requirements of a highway sign are that it be legible to those for whom it is intended and that it be understandable in time to permit a proper response. Desirable attributes include: High visibility by day and night; and high legibility (adequately sized letters or symbols, and a short legend for quick comprehension by a road user approaching a sign).

    Section 2A.07 – Retroreflectivity and Illumination: Regulatory, warning, and guide signs and object markers shall be retroreflective or illuminated to show the same shape and similar color by both day and night, unless otherwise provided in the text discussion in this Manual for a particular sign or group of signs.The requirements for sign illumination shall not be considered to be satisfied by street or highway lighting.

Nighttime driving statistics

The ability to perceive and judge distance is severely impaired at night due to lack of ambient light night driving is a top cause of car accidents. Statistics enforce this increased danger:

More than 40 percent of all fatal car accidents occur at night.

The fatal crash rate of 16-year-olds is nearly twice as high at night.

States with nighttime restrictions in place have reported up to a 60 percent reduction in crashes during the restricted hours.

Only 14 percent of the miles driven by 16- to 17-year-old drivers occurred between 9 p.m. and 6 a.m., yet this time period accounted for 32 percent of fatal crashes in this age group.

Among teen nighttime crashes, 58 percent happen between 9 p.m. and midnight.

According to "Characteristics of Unrestrained Passenger Vehicle Occupant Fatalities 16 and Older in Motor Vehicle Traffic Crashes by Time Of Day" (published by NHTSA, May 2008), the teen driver fatality rate per vehicle mile of travel is about three times higher at night than during the day.According to NHTSA 2008 data, states with nighttime driving restrictions show crash reductions of up to 60 percent during restricted hours.

Retroflectivity Requirements

The 2009 Manual on Uniform Traffic Control Devices (MUTCD) Section 2A.08, Maintaining Minimum Retroreflectivity, is current. That Section did not change as a result of 2012 updates to the MUTCD. Only the compliance dates were revised.

Section 2A.08 of the MUTCD sets standards for maintaining minimum retroflectivity. The final standard reads: "Public agencies or officials having jurisdiction shall use an assessment or management method that is designed to maintain sign retroreflectivity at or above the minimum levels in Table 2A-3."

The table sets the standards based on the ASTM D4956 standard for retroreflective sheeting and provides criteria for allowances for standard DOT signage for beaded and prismatic sheeting in posted and overhead conditions.

MUTCD specifications

The MUTCD specifications set minimum standards for standardization, classification, use, design, color, dimensions, conspicuity, location, and orientation as well as retroreflectivity. The retroreflectivity should be assessed by a trained sign inspector “conducting a visual inspection from a moving vehicle during nighttime conditions” according to Section 2A.08.

Life span of signs

When signs are installed, the installation date is labeled or recorded so that the age of a sign is known. The age of the sign is compared to the expected sign life. The expected sign life is based on the experience of sign retroreflectivity degradation in a geographic area compared to the minimum levels. Signs older than the expected life should be replaced.

FHWA management policy for sign maintenance and replacement in place

The use of a retroreflectometer can be used to assess illumination. Blanket replacement can be recommended where it appears necessary, and control studies can also assess performance in a given area.

ASTM D4956 retroreflective sheeting specifications for materials for traffic signs

The ASTM standard 4956 provides properties of retroreflective sheeting in a numbered system according to type of retroreflectivity. Types I and II are engineer grade deemed least reflective of all materials with the narrowest viewing angle, least durable and not approved by many DOT agencies.

ASTM type III carry high intensity beaded designations reflecting about 5 times more light than engineer grade and at a much wider angle, and are more durable and longer lasting.

ASTM type IV and up are designated Diamond Grade or prismatic and exceed ASTM D4956 proposed Type XI Specifications. These are the most reflective; reflecting about 10 times more light than Engineer Grade and at a very wide angle and are slightly more durable than High Intensity. These signs are currently required by most states for all or most highway and traffic signs.

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