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16 There may be overtime or shift differential pay for some of plan to implement. Several of the DOTs were exploring cali- the inspections; however, it was not queried in the survey. bration signs, but have not formalized procedures. One DOT was using a retroreflectometer to measure signs that were Another important aspect of this method concerns the recently replaced to find signs that were at or near the mini- inspection intervals or frequencies. The MUTCD does not state mum levels to be used in the calibration procedures. There how frequently signs should be inspected, whether once per was one sign sheeting manufacturer that began producing year or once every two years. There were several agencies that comparison panels; however, there were no respondents that consistently inspected all roadway signs each year; however, were aware of the manufacturer's product before the surveys inspection intervals ranged from four per year to once every were conducted. There was some confusion with the sup- five years. The agency with a five-year interval was conserva- portive technique requirements and this was one area where tive with inspections and more likely to remove any question- participants thought more guidance would be helpful. able signs. One respondent expressed the opinion that when the inspection interval was longer, there was a higher possibility of having inadequate signs on the roadway. Conducting nighttime Measured Retroreflectivity inspections once per year appears reasonable, but this study did Measured retroreflectivity was the least selected method and not identify any optimal inspection interval. most agencies did not consider it as a primary method for maintaining minimum sign retroreflectivity. The LTAP cen- Visual nighttime inspection can also be used as a second- ters surveyed strongly recommended other methods because of ary or temporary support method. One agency needed to con- the high cost for a retroreflectometer and for the considerable duct a quick assessment of the overall sign population and demand on labor and time. Again, there were two different types utilized nighttime inspection to sample various roadways in of retroreflectometers and each cost approximately $10,000 to the county to better understand the quality of the existing $12,000 per unit. Most agencies are currently trying to do more signs for a cost analysis. The nighttime inspection of sam- with less and the purchase of a r etroreflectometer was not a pled roadways revealed that approximately one-third of the cost-effective option. Along with the initial cost, measuring a signs were inadequate. Consequently, the agency elected to large sign population can be a substantial drain on manpower. implement an expected sign life method in an attempt to save Some of the surveyed DOTs possessed a retroreflectometer and adequate signs as opposed to wasting resources in a county- used it for periodic sampling; a few local agencies also own a wide blanket replacement. One of the benefits of visual retroreflectometer and several had the ability to borrow a unit nighttime inspection cited most often was maximizing sign from an LTAP center. service life. One participant mentioned that Type III signs between 10 and 15 years old would typically look fine during The Minnesota DOT's Traffic Sign Maintenance/ inspections. One DOT noted that this method can extend the Management Handbook (22) states that data collectors use of some signs for up to 20 years. following the ASTM E1709-00e1 standard can measure approximately 20 signs per hour, although a lower rate of 10 The MUTCD does state that "the retroreflectivity of an to 15 unwashed signs per hour was documented in a 2011 existing sign is assessed by a trained sign inspector" (1). TRB publication (23). In this study, the data collection pro- Some of the DOTs had established training programs that cess measured between 80 and 120 signs per day. The higher consisted of field demonstrations and/or instructional mate- rate was only achieved once and was the result of continuous rials. One DOT placed signs of various retroreflectivity lev- favorable shoulder conditions and signs that were spaced close els along a local racetrack and maintenance personnel were together. Measurements take time and can be a tiring process trained to find the substandard signs. Another DOT had a if readings are collected over prolonged periods of multiple computer-based training course that provided examples and hours. The measurement rate is also heavily dependent on the descriptions of failed signs and an inspector would complete roadway conditions and the location of the sign. a short test that was kept on record. It was mentioned that certain LTAP centers also provided training courses, but the Based on past data collection experience, some measure- majority of the participants relied on past experience and on- ments may be difficult and time-consuming to obtain as a result the-job training. It was common to hear that many inspectors of physical barriers, sign height, and shoulder conditions. Some had between 10 to 20 years of job experience. retroreflectivity measurements may require that technicians use a ladder or a truck with a boom lift. Bridges, guardrails, unstable For additional resources on visual nighttime inspection, roadway shoulders, limited sight distance, overhead mast arms, the MUTCD refers readers to 2007 FHWA publication Main- and nearby railroad tracks are just a few examples of difficult taining Traffic Sign Retroreflectivity (FHWA-SA-07-020) measurement conditions. High-speed and high- volume road- (14). In that publication, FHWA recommends that an agency ways may also place sign technicians in undesirable locations use one or more supportive techniques for nighttime visual where it would be prudent to have additional traffic control. assessments, including consistent parameters, calibration There are ample opportunities to measure signs on a roadway signs, and comparison panels. Apart from training, most for a control sign sample or study; however, some sign mea- agencies had not decided which supportive technique(s) they surements may not be worth the time and effort.