Andrew Holick

Estimates of Work Zone Exposure on the National Highway System in 2001

A comprehensive set of data on work zone exposure characteristics does not exist at the national level. Without accurate work zone exposure data, it is impossible to know whether changes in work zone performance measures (safety, congestion, public sentiment) over time are due to true changes in the characteristics of work zones or to changes in external factors. Presented are the results of a study exploring the quality and quantity of work zone data available in the United States. During this study, researchers collected data in five regions across the country. The regional data were then extrapolated to develop national estimates of several work zone exposure characteristics on the National Highway System (NHS) during 2001. Researchers examined constructionmanagement databases, traffic control plans, and project-inspector diaries on projects performed by private contractors in these regions during 2001. Researchers also gathered data on work zone activities that were performed directly by transportation agency in-house personnel in each of the regions. These data were then extrapolated to national estimates of several work zone exposure measures during the 2001 calendar year, including the percentage of NHS that experienced at least 1 day of work zone activity in 2001; length, duration, and frequency of activity in work zones on the NHS; impacts of work zones on available NHS roadway capacity; and vehicle exposure to active and inactive work zones on NHS during the year.

Maximizing legibility of unlit freeway guide signs with clearview font and combinations of retroreflective sheeting materials

The legibility of full-scale guide signs was evaluated in a controlled field study. The objective was to determine how the legibility of unlit guide signs could be maximized with combinations of font and retroreflective sheeting. Two fonts were tested: Series E (Modified) and Clearview 5WR, a modified version of Clearview 5W. Five combinations of retroreflective sheeting were also evaluated. The study included 30 subjects split into three age groups. Without informing the subjects, the researchers varied headlamp output to evaluate the legibility of various sign lighting levels. The results of the study clearly show that the most legible combination of font and retroreflective sheeting (of those tested) is the Clearview 5WR font and microprismatic legends on beaded, high-intensity backgrounds. Although the combination of microprismatic legends and backgrounds performed statistically equivalently to microprismatic legends on beaded, high-intensity backgrounds (in term of legibility distances), the research shows that the higher luminance contrast and lower costs associated with the latter combination make it a much more attractive application.

Model of overhead-sign luminance needed for legibility

Photometric models can be used to estimate the sign luminance provided for different roadway scenarios. While photometric models provide specific luminance curves, no standards or design criteria exist that can be used to define how much luminance is needed by a driver. For instance, if one desired to design a sign based on an assumed design driver and other pertinent criteria, no guidelines or models are available. An analysis has been designed to develop a model for determining the minimum luminance needed to read overhead guide signs. The model was developed based on legibility data collected for defining the minimum luminance needed to read everyday words on overhead guide signs.

2005 D. Grant Mickle Award: Outstanding Paper on Operations and Maintenance Maximizing Legibility of Unlit Freeway Guide Signs with Clearview Font and Combinations of Retroreflective Sheeting Materials

The legibility of full-scale guide signs was evaluated in a controlled field study. The objective was to determine how the legibility of unlit guide signs could be maximized with combinations of font and retroreflective sheeting. Two fonts were tested: Series E (Modified) and Clearview 5WR, a modified version of Clearview 5W. Five combinations of retroreflective sheeting were also evaluated. The study included 30 subjects split into three age groups. Without informing the subjects, the researchers varied headlamp output to evaluate the legibility of various sign lighting levels. The results of the study clearly show that the most legible combination of font and retroreflective sheeting (of those tested) is the Clearview 5WR font and microprismatic legends on beaded, high-intensity backgrounds. Although the combination of microprismatic legends and backgrounds performed statistically equivalently to microprismatic legends on beaded, high-intensity backgrounds (in term of legibility distances), the research...