2003-09-25_PWETC_AgendaPacket - Laserfiche WebLink

Home

NOT/CEJ- . ,HIS MATERIA[ J\~ CO~YRlGHlI.A II! J MAY BE PROTECTEQ . II.fJ.E JZ U, s. .CODEI FREEWAY ACCIDENTS AND IllUMINATION Paul C. Box, Paul C. Box and Associates, Skokie, illinois The findings of a study of freeway accidents and iliumination are reported. The time during which ambient light conditions are such that typical road- way iliumination wouid have an effect was found to be from 15 min after sunset to 15 min before sunrise. Lighted freeways were found to have lower (better) night-day accident ratios than unlighted ones. The lighted freeways With the lowest iliumination, averaging 0.6 horizontal footcandles maintained, had the best accident ratio. This corresponds to an initial iliumination design level of about I. 0 HFC. A wide variation was found in average illumination between adjacent pairs of luminaires along o\3pecific freeway sections. This was found to be principally a result of differences in individual lamp output. The varIations of HFC averages and uniformity are so great as to cast doubt on the real value of these elements In lighting design calculations. eIN THE 1966 public lighting needs report to the U. S. Congress, data were presented from pilot studies of freeway accidents (I). Information was related to estimated vehicle-miles of travel, night-day accident ratios, illumination levels, and uniformity. Apparent trends were found in reduced night-day accident ratios (hence, actual reduc- tions in accidents) with increased illumination and with improved uniformity. However, the illumination levels were calculated in-service values as reported by the responsible public agencies. A study, undertaken in the illuminating Engineering Research Institute, was de- signed to expand the data base and to attempt definition of optimum illumination ievels and uniformities from the standpoint of accident reduction. In the execution of the study. careful attention was given to tabulation of accidents from the reports themselves (to eliminate computer data errors) and to collection of traffic volume counts. The attempt was made to include a wide variety of urban and suburban freeway conditions, such as number of lanes, traffic volumes, and illumination levels and uniformities, including no illumination. Data were gathered from metropolitan areas of Toronto, Chicago, Atlanta, Dallas, Phoenix, and Denver. There were 203 miles of routes and more than 21,000 accidents included in the summary. Items tabulated from each accident report included time of accident and weather condition, accident severity, type of accident, portion of freeway roadway on which the accident occurred (main line, ramp exit from main line, ramp entrance to main line, and entirely within the ramp itself), and age of the driver who struck another object or who ran off the road (not necessarily the driver who was iegally responsible for the accident). Figure 1 shows the card used to code the acci,dent data, and Table 1 gives a summary listing of all routes that were studied. From the standpoint of tabulation, a location type of accident file is highly desirable. The tabulation of accident data from copies of the police report can be time-consuming, but it appears to be a necessary control. The number of accidents directly relatable to freeway illumination was found to vary widely in the check between actual tabulations and data processing printouts. In a check of 3 systems, differences of 19 to 62 percent were found. DAY-NIGHT THRESHOLD POINT An important initial step in the project was to find a method of accurately relating freeway accidents and traffic volumes to illumination. This, in part, required 10 .,. ,,~