It was determined in 1980 that approximately a quarter of New York State's 15,000 inductive loop detectors, used to control traffic signals, were out of order at any given time and were maintenance-free for an average of only 2 years. A study was made to find the major causes of loop failures and how to reduce them. Installation methods in New York and elsewhere were investigated, and hundreds of failed loops were studied to find failure types and causes. Data suggested that failure was mainly caused by improper installation, inadequate loop sealants, or wire failure. Encased wire (regular signal wire protected by continuous smooth-bore polyethylene tubing), which provided greater freedom of movement in areas of pavement distress, was being evaluated in other states. Also, instead of diagonal cuts at the corners of the loop, it was decided to cut the corners at 90-degree angles and then chisel or core them, thus saving sawing time and equipment wear and also having negligible impact on the loop wire itself. Another cause of failure is damaged or broken wire because of its floating to the surface of the sealed slot, which can be avoided with a simple hold-down device. Other recommendations included saws with greater horsepower, and complete pressurized washing and drying of the saw slot to enhance sealant bond. Laboratory tests were developed to evaluate sealants before purchase to assure that those used would provide strength, longevity, water resistance, good bond to the pavement, flexibility, wire encapsulation, and ease of installation. New York's new methods and materials appear to be the best currently available, and a program has been established for continued evaluation of these detector systems. A special training video tape is now available that covers these new materials and procedures.

Media Info

  • Media Type: Print
  • Features: Figures; References;
  • Pagination: pp 76-80
  • Monograph Title: Traffic control devices and rail highway crossings
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00452656
  • Record Type: Publication
  • ISBN: 0309038227
  • Files: TRIS, TRB
  • Created Date: Aug 27 2004 9:59PM