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Appendix A: Visibility and Retroreflectivity

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Section 1: Overview

In general, for pavement markings to be effective, they must be visible both day and night. The Texas Manual on Uniform Traffic Control Devises (TMUTCD) clearly states “Markings which must be visible at night shall be retroreflective unless ambient illumination assures adequate visibility.” During the day, drivers receive critical navigation information from the roadway and surroundings and do not necessarily need to rely heavily on pavement markings to provide such information. At night, however, the visibility of the roadway and surroundings drops dramatically. Because pavement markings contain glass beads that make them visible at night, drivers rely heavily on marking visibility to provide them with short-range and long-range navigation information. The ability to actually see a pavement marking at night is not solely a function of the reflective characteristics of the pavement marking, but is dependent upon several factors, including:

  • the amount and pattern of light produced by a vehicle’s headlights
  • the amount of light reaching the pavement marking
  • the visual characteristics of the observer
  • the retroreflective characteristics of the pavement marking.

While transportation agencies can do little to control the first three items in the above list, the retroreflective characteristics of the pavement marking can be controlled and are the focus of this chapter:

  • Section 1 presents an overview of pavement marking visibility and retroreflectivity.
  • Section 2 describes general retroreflectivity concepts pertaining to pavement markings.
  • Section 3 describes the retroreflectivity needs of drivers.
  • Section 4 describes portable retroreflectivity measurement devices.
  • Section 5 provides guidance in the use of mobile retroreflectometers as tools for management of pavement markings.
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