Click for next page ( 4


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 3
3 chapter one Introduction Roadway traffic signs are a primary means of communicating table containing minimum sign retroreflectivity values to the critical information to roadway users. The Manual on Uni- Manual (section 2A.08 of the 2009 MUTCD). In addition, form Traffic Control Devices (MUTCD) provides the basic several methods are identified that agencies can implement principles that govern the design and use of traffic control to maintain traffic signs at or above the minimum retro devices for all roadways open to the public (1). There are five reflectivity requirements. The next section expands on both main principles in the MUTCD that traffic control devices the requirements and approved maintenance methods. must follow: Establishing sufficient and acceptable minimum retro 1. Fulfill a need, reflectivity levels has been an ongoing collaboration of 2. Command attention, several different studies. In 1993, Paniati and Mace (3 ) 3. Convey a clear simple meaning, established minimum requirements for regulatory, warn 4. Command respect from road users, and ing, and guide signs. The researchers developed a computer 5. Give adequate time for proper response. analysis program that incorporated various driver, v ehicle, and roadway parameters. The program computed the mini Traffic signs are also classified into three primary des mum required visibility distance for various inputs, which ignations: regulatory, warning, and guide signs. Each clas ultimately generate minimum retroreflective values. In sification serves a distinct purpose and adheres to strict 1995, Mercier et al. (4) confirmed that Paniati and Mace's and uniform design standards. Regulatory signs inform minimum requirements would sufficiently meet the needs of traffic laws or regulations, warning signs give notice of of an aging driving population. This research team mea a situation that might not be readily apparent, and guide sured the luminance thresholds for various traffic signs signs provide destination information such as directions, in a laboratory setting and determined that the m inimum distances, and points of interest. Sign information can be levels would meet the needs of 85% or more of all drivers. conveyed through the legend, which can be comprised of In 2004, Carlson and Hawkins (5) established the final words, symbols, and arrows. Road users can also extract FHWA minimum retroreflectivity requirements, those that information from a sign's unique appearance, with size, are used today. Their research utilized methods from the color, and shape critical components. In addition to the Paniati and Mace study, but incorporated new inputs to specialized design criteria, road users need to detect signs reflect recent developments in vehicle headlamps, changes and comprehend the message content in a timely manner in in fonts, vehicle types and sizes, drivers' nighttime needs, both daytime and nighttime. At night, signs not internally and the latest sheeting materials. Carlson and Hawkins also illuminated must be fabricated with retroreflective materi employed a new analysis tool that computed r etroreflectivity als. Light from a vehicle's headlamps is reflected from the requirements for traffic signs in various positions (right, left, sign's surface back to the driver giving the sign an illumi and overhead) on the roadway. The final minimum levels nated appearance. were adopted by FHWA and are contained in Table 2A-3 of the 2009 MUTCD (1). The requirements exclude blue and brown signs and also parking, walking/hitchhiking/ Background crossing, pedestrian, adopt-a-highway, and bike signs. Also restricted are the uses of specific retroreflective materials in In 1993, the Secretary of Transportation was required by certain sign applications. Congress to revise the MUTCD to include "a standard for a minimum level of retroreflectivity for pavement markings Merely establishing and documenting minimum retro and signs which apply to all roads open to public travel" (2). reflectivity levels was not the sole objective. The key element The goal of the new minimum retroreflectivity requirements in the standards is maintaining sign retroreflectivity at or above was to improve safety on our nation's streets and highways, the minimums. To establish a level of compliance, FHWA and was meant to ensure that drivers, especially the elderly, established three important compliance dates (on August 31, would be able to detect, comprehend, and react to traffic signs 2011, a notice of proposed amendments was published in the accordingly and help to facilitate safe, uniform, and efficient Federal Register recommending that the compliance dates travel. To satisfy the congressional directive, FHWA added a for sign retroreflectivity be modified. As of March 2012,