Click for next page ( 44

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 43
43 Appendix D Myths and Other Frequently Asked Questions During this project it became obvious that there were a variety of questions about the new minimum sign retroreflectivity requirements that were unanswered and the amount of misinformation was growing. FHWA has a document addressing some of the questions here: Other myths or frequently asked questions are listed here with brief answers. On-the-job experience is a substitute for training for nighttime inspection. This is not true. FHWA has provided LTAP with training slides that describe the importance of nighttime sign visibility, the basics of retroreflection, the methods listed in the MUTCD, a link between the methods in the MUTCD and the minimum retroreflectivity levels, and how to perform each of the assessment methods. A hand-held retroreflectometer is required to meet the new MUTCD requirements. This is not true for all methods. How- ever, there are methods that do require the use of a retroreflectometer. There are alternatives to purchasing retroreflectometers. For instance, retroreflectometers are available through LTAPs and are also available for rent. All signs have to be replaced by a certain date. By January 2015, only the shoulder-mounted signs (except street name signs) listed in Table 2A-3 that fail to meet the minimum retroreflectivity levels need to be replaced. By January 2018, all overhead signs and street name signs need to be in compliance with the minimum retroreflectivity levels. Right now there are no mini- mum retroreflectivity levels for blue and brown signs. (On August 31, 2011, a notice of proposed amendments was published in the Federal Register proposing to modify the compliance dates for sign retroreflectivity. As of January 2012, FHWA have not responded to the comments. For the latest information, see Warranty is the same as service life or minimum retro value. As described in the this report, the warranty period of sign sheeting is generally much less than the in-service life based on minimum retroreflectivity levels. The cheapest sheeting is the most cost-effective. Many life-cycle cost analyses have shown that the cheapest sheeting is not the most cost-effective when the life-cycle cost is considered. The most expensive sheeting is the best. Again, life-cycle cost analyses show that the most expensive sheeting materials are not the most cost-effective. Agencies must weigh the initial cost of the sheeting materials versus their expected life, which can vary in different regions of the country and is typically much longer than the warranty period that sign sheeting manufacturers provide. Engineering grade material is not allowed now. For some sign types, this is true. Engineering grade sheeting (or ASTM Type I material) is not allowed for yellow or orange warning signs and for the legend on guide signs and street name signs. A computer inventory is required. No sign inventory is required. However, there are many benefits of having a sign inven- tory as described in the report. You must have a 60-year old for nighttime inspection. There are three different visual nighttime inspection procedures that can be used. The procedure that FHWA calls "consistent parameters" does require an inspector to be at least 60 years of age. The other two visual nighttime inspection procedures do not have set criteria on the age of the inspector. All nighttime inspections are alike. There are actually three specific visual nighttime inspection procedures that FHWA has spelled out. A description of the procedures can be found in Appendix A. If you implement the blanket replacement method you can forgo routine maintenance. This is not true. There are many other aspects of signing that need to be maintained besides retroreflectivity. For examples, there are knockdowns, vandalism, and vegetation that all need constant maintenance to ensure that the signs perform as intended. Sign retroreflectivity can be assessed during a daytime inspection. While it may be possible to judge the relative age of a sign during daytime inspections (mostly based on the color), it is less than reasonable to judge retroreflectivity. Some agencies

OCR for page 43
44 have tried using a spotlight during the day or flashing their high beam lights. However, there is too much subjectivity in these methods to be considered reasonable. Frost or dew does not affect retroreflectivity. When frost or dew is detected during sign inspections, the inspections should stop and be scheduled for another night. The ability for a sign to properly retroreflect light in conditions of frost or dew is significantly diminished. Retroreflectivity can be assessed by nighttime photos. As FHWA explains in its literature, using photographs of signs is not an acceptable method to judge retroreflectivity. The amount of light and the proximity of the light to the camera can make a perfectly good sign look bad or vice versa. This is why FHWA does not publish photographs of traffic signs with retroreflec- tive levels printed next to the sign. Retroreflectometers are precision instruments that produce perfect results with no variation. The ASTM committee is working on the development of a precision and bias statement for the handheld retroreflectometers for Test Method E1709. Recently a research report from Indiana used 22 stop signs and three different retroreflectometers in a laboratory test to deter- mine the range of median bias for Type I and Type III sheeting for both the legend and background (white and red). Here is what they found: Type I background ranged from 1 to 3 cd/lx/m2; Type III background ranged from 2 to 4 cd/lx/m2; Type I legend ranged from 3 to 12 cd/lx/m2; and Type III legend ranged from 15 to 40 cd/lx/m2. They also made field measurements with the handhelds. They concluded that it is reasonable to assume that the coefficient of variation for an individual sign will be between 4% and 14% when using a handheld device. The paper was published in the ITE Journal of Transportation (March 2011). The Highway Innovative Technology Evaluation Center funded a study in 2004 to investigate the bias of retroreflectivity mea- surements. The draft final report shows measurement bias of some prismatic sheeting materials as much as 25%. This is similar to statements in ASTM E1709 concerning differences in measurements using different types of handheld retroreflectometers.

OCR for page 43
Abbreviations used without definitions in TRB publications: AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACINA Airports Council InternationalNorth America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation