Manual of Traffic Signs
Retroreflective Sign Sheetings



Introduction

Important Note: The state of the retroreflective sheeting market continuously changes, due to development of new sheetings, requested changes to ASTM D4956, and changes in product offerings by manufacturers.

For nearly all traffic signs on public roadways in the United States, the faces of these signs are covered with a thin plastic material known as retroreflective sheeting. This material is designed to show a bright and uniform color and to reflect light back to a viewer's eyes so as to be visible in both daylight and darkness. If properly applied and sealed to a good surface, nearly all retroreflective sheetings are water, ice, and salt resistant and durable under normal outdoor conditions. To provide color, the sheeting either has colored pigments built into or applied to the material or has a translucent colored overlay film.

In the early days of highway travel, traffic signs were painted using common paints, and were either nonreflective or had retroreflectivity added by mixing glass beads in the paint or by using glass spheres or reflectors in the sign legend. Painted signs have not been in common use for over half a century.

There are two national specifications that define types of retroreflective sheeings - AASHTO M268 or ASTM D4956. The types used in the ASTM D4956 specifications do not necessarily imply relative performance; i.e. a "higher"-type sheeting isn't necessarily better than a "lower"-type sheeting - it just meets different performance characteristics. Also note that some sheetings on the market can meet the criteria of several ASTM types. The chart below describes each type of sheeting, sorted by its categorization under ASTM D4956.


Retroreflective Sheeting Types

AASHTO M268 Type ASTM D4956 Type Status Description Typical Uses

(none)

I

Limited Use Trade name: Engineer Grade. Basic reflective sheeting, made up of either very small glass beads enclosed in a translucent pigmented substrate or a dual-layer prismatic sheeting with moderate retroreflectivity. Has no distinctive identifying pattern, other than, of course, it reflects. This material is one of the most durable (in its ability to withstand rough handling) of all retroreflective sheeting products. Generally regarded to have a seven year service life.
  • Vehicle graphics
  • Advertising signs
  • Conspicuity markings
  • No longer in general use for traffic signs

II

Limited Use Trade name: Super Engineer Grade. Similar to Type I, except it uses larger glass beads in a denser matrix, providing about twice the level of reflectivity of Type I sheeting. This sheeting can be identified by small trademarks which are screened into the sheeting (varying by manufacturer). Also very durable. Generally regarded to have a ten year or greater service life.
  • Vehicle graphics
  • Advertising signs
  • Conspicuity markings
  • No longer in general use for traffic signs

A

III

Limited Use Trade name: High Intensity Grade. This is an "encapsulated lens" sheeting, made of 2 layers - an outer translucent colored or clear layer, and an inner reflective layer faced with glass beads. The two layers are connected by a lattice, hence its distinctive 'honeycomb' appearance, where the lattice pattern varies by manufacturer for easy identification. Generally regarded to have a ten year service life.
  • Superseded by newer alternatives such as Type IV

B

IV

Current Trade names: High Intensity Prismatic or Microprismatic Grade. This is also a multi-layer sheeting, except that the reflective layer is made of microscopic cube-corner reflectors instead of glass beads - known as a "microprismatic" layer. This sheeting can be distinguished by a pattern of small squares or bars superimposed upon the lattice grid. Generally regarded to have a ten year service life.
  • All types of post-mounted signs
  • Barricades and other rigid temporary traffic control devices

(none)

V

Limited Use A sheeting made of a metallized microprismatic material. Intended for applications requiring flexibility and durability. Generally regarded to have a five year service life.
  • Cones, delineators, and other flexible channelizing devices
  • Roll-up signs
  • Vehicle graphics
  • Conspicuity markings

VI

Limited Use A vinyl backed beaded or microprismatic material. This sheeting differs from all other types by being composed of a flexible cloth. Generally regarded to have a two year service life, depending on handling and use.
  • Roll-up signs
  • Retroreflective clothing
  • Retroreflective flags, patches, and similar items

(none)

VII

Discontinued Trade name: Diamond Grade LDP. A microprismatic sheeting distinguished by a diamond-shaped lattice separating the sheeting layers, a "coarse" grain to the microprisms, and high retroreflectivity levels at shallow viewing angles. Generally regarded to have a ten year service life.
  • No longer manufactured (superseded by Type XI)

B

VIII

Current Trade names: Crystal Grade, Maximum Visual Performance Grade. A microprismatic sheeting similar in design to Type VII and IX, but with distinguishing characteristics similar to Type IV. Generally regarded to have a ten year service life.
  • Post-mounted signs
  • Overhead signs
  • Internally-illuminated signs
  • Barricades and other rigid or semi-rigid temporary traffic control devices

IX

Current Trade names: Diamond Grade VIP, Omniview, Oralite. A microprismatic sheeting very similar to Type VII, distinguished by a "fine" grain of the microprisms. This sheeting provides relatively high retroreflectivity levels at a wide range of viewing angles. Generally regarded to have a ten year service life.
  • Post-mounted signs
  • Overhead signs
  • Internally-illuminated signs
  • Signs with fluorescent backgrounds

(none)

X

Discontinued A microprismatic sheeting very similar to Types VII-IX, and has similar performance characteristics. Generally regarded to have a ten year service life.
  • Many Type X sheetings reassigned into Type VIII

D

XI

Current Trade names: Omnicube, Diamond Grade DG3. A microprismatic sheeting very similar to Types VII-IX, but providing high retroreflectivity at both shallow and wide angles. Generally regarded to have a ten to twelve year service life.
  • Post-mounted signs
  • Overhead signs
  • Internally-illuminated signs
  • Signs with fluorescent backgrounds
  • Barricades and other rigid temporary traffic control devices

Nearly all sheetings are available with pressure-sensitive backings for attachment to sign surfaces. In the past, sheetings were available with heat-activated backings, but with changes in sign manufacturing technology this type of adhesive is no longer widely used.


Sign Legends

Legends (letters, numeral, symbols, and borders) for traffic signs are produced by the following methods:

Colored inks or pigments used in screen or electronic printing are translucent to allow reflectivity through the ink, whereas black ink used for signs is opaque.

Some sign sheetings can be sensitive to visual orientation; i.e. the retroreflective performance can vary with the angle at which the sheeting is placed on the sign panel. If a sheeting is susceptible to this effect, it should be used in the orientation recommended by the manufacturer, especially if used for cut-out or demountable legends.


End of Service Life

Sign sheetings generally reach failure in different ways:
Single-layer glass bead sheetings usually fail by gradually losing their retroreflective intensity. This is due to increasing opacity of the pigmented material caused by ultraviolet ray exposure due to sunlight. This can result in a sign that looks good in daytime but is difficult to read at night. After extended exposure (20+ years), this sheeting will crack and peel from the sign substrate.
Multi-layer sheetings can fail structurally upon reaching the end of their service lives due to exposure to ultraviolet rays and weather, even if retroreflectivity values are within minimum levels. The outer colored layer delaminates and falls off, exposing the underlying reflective layer to the elements, and ruining the contrast needed for legibility.
Signs can also fail due to peeling, curling, or delamination of the sign legend or overlay film due to weather exposure or other factors.
Sign inks can also fade after long sun exposure and lose contrast with the surrounding sheeting, rendering the legend difficult to read.

The Manual on Uniform Traffic Control Devices now requires agencies to replace signs that have reached the end of their service lives. This can be based on the following methods:

  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. Signs that are visually identified by the inspector to have retroreflectivity below the minimum levels should be replaced.
  2. Measured Sign Retroreflectivity: Sign retroreflectivity is measured using a retroreflectometer. Signs with retroreflectivity below the minimum levels should be replaced.
  3. Expected Sign Life: 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.
  4. Blanket Replacement: All signs in an area/corridor, or of a given type, should be replaced at specified intervals. This eliminates the need to assess retroreflectivity or track the life of individual signs. The replacement interval is based on the expected sign life, compared to the minimum levels, for the shortest-life material used on the affected signs.
  5. Control Signs: Replacement of signs in the field is based on the performance of a sample of control signs. The control signs might 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. All field signs represented by the control sample should be replaced before the retroreflectivity levels of the control sample reach the minimum levels.
  6. Other Methods: Other methods developed based on engineering studies can be used.


Special thanks to Seth Chalmers of Dibble Engineering, H. Gene Hawkins Jr. of Texas A&M University, and Paul Carlson of Road Infrastructure Investment Holdings for their invaluable assistance in gathering this information.



Updated 03 September 2019 (information substantially revised, coded into new format)
Scripting: Richard C. Moeur

All text and images on this page © Richard C. Moeur. All rights reserved.
Linked sign layout files in PDF format provided courtesy of FHWA's MUTCD website
Unauthorized use of text, images, and other content is strictly prohibited. Refer to Copyright, Disclaimer, and Standard Use Agreement for details.