This project was undertaken to compare operational and safety characteristics of leading versus lagging protected left turn operation. The measures of effectiveness included field measured intersection delay with leading and with lagging left turns. Intersections in Pima County, Glendale, Tempe and Mesa, Arizona were studied with both leading and lagging operation. Intersection delay studies were also done with first car versus third car actuation of leading protected left turn phases. Signal progression was studied with leading, lagging and combination of leading and lagging left turns which provided the best progression. This evaluation was accomplished with an instrumented vehicle and travel time runs throughout a grid. Accident studies were conducted in Tucson, Pima County and Scottsdale, Arizona. These studies compared accident frequency before and after the conversion from leading to lagging left turns. A public opinion survey was conducted to obtain motorists' preference of leading or lagging left turns.

Project Summary

Passing and climbing lanes provide additional lanes for vehicles to safely pass other vehicles while maintaining speeds. Implementing passing and climbing lane projects provides traffic operational and safety benefits at a cost that is far less than fully widening a highway. In an effort to enhance safety and mobility on Arizona's roadways, the Arizona Department of Transportation is currently updating the 2003 Passing and Climbing Lanes Prioritization Study. This update intends to further refine the identification and prioritization methodology previously utilized and to develop a prioritized list of candidate locations that would provide the most benefit to the traveling public.
Study Objectives

    Review previous studies and research current best practices.
    Analyze the safety and performance benefits of passing/climbing lanes constructed since the previous study.
    Develop a revised methodology and ranking criteria.
    Obtain feedback from ADOT District Engineers and other stakeholders, such as rural COGs and MPOs.
    Develop a new prioritized list of candidate passing/climbing lane projects. 
 

The study objective was to identify a lighting system which has a lower power cost and reduced maintenance requirements and which provides adequately for motorists' needs in terms of legibility and illumination level. Twenty-five candidate lighting systems were identified through a review of technical data and specifications for lamps and fixtures by an independent lighting expert. Photometric tests and computer analyses of sign illumination levels reduced the number of candidates to ten alternative systems which were then field tested. Each alternative lighting system was tested for 10 to 14 months. Sign luminance was measured with a telephotometer. Power consumption was monitored. Maintenance requirements and lamp life were noted. A human factors study determined legibility distance and rated viewing comfort, lighting uniformity, and color rendition. An economic analysis was performed which considered the initial cost of acquiring and installing the lighting systems and annual costs for electric power, washing, relamping, and ballast replacement. A lighting system using the high pressure sodium light source was recommended. Compared to the existing commonly used fluorescent system, it uses one-third as much electric power and has about one-third of the annual owning and operating cost. The recommended system has a satisfactory illumination level and provides the best legibility distance of the ten systems tested.