#02 - Cross Walk Discussion - Laserfiche WebLink

Home Browse Search

could simply be divided by an hourly adjustment factor of 4.2 percent (0.042) to get the all-day volume. In reality, though, hourly volumes vary throughout the day with greater pedestrian activity during certain peak periods. Suppose that 10 out of 100 (10 percent) of the day’s pedestrians are counted between 5 p.m. and 6 p.m. If that hour’s count were divided by 0.042, the true daily volume would be overestimated (10 / 4.2 percent = 238). Likewise, if 2 out of 100 (2 percent) are counted between 3 a.m. and 4 a.m., dividing that count by 4.2 percent would underestimate the true daily volume (2 / 0.042 = 48). Therefore, adjustment factors for each hour of the day are needed to obtain a more accurate estimate of the true daily volume. The adjustment factors were derived from two data sets. First, all-day (8- to 12-hour) pedestrian counts were undertaken at 11 marked crosswalks and 11 unmarked comparison sites. Second, adjustments were calculated based on the method used by Zegeer et al. for 24-hour pedestrian counts in Seattle, WA.(39) They found that the 12-hour period from 7 a.m. to 7 p.m. represented 86 percent of the 24-hour daily pedestrian volume. Separate adjustment factors were used for each area type (CBD, fringe, and residential), because the area types have different patterns of hourly pedestrian volume. It was determined that crosswalks and comparison sites had similar pedestrian volume distributions by the time of day, so the same adjustment factor was used for a crosswalk and its matched comparison site. The adjustment factors by time of day and area type appear in table 12. The 1-hour pedestrian counts at each crosswalk and comparison site were divided by the appropriate factor to obtain the 24-hour daily pedestrian volume. For example, suppose 100 pedestrians were counted between 9 a.m. and 10 a.m. at a CBD location. Then the daily pedestrian volume was estimated to be 100 / 4.9 percent = 2,041 pedestrians. At a fringe location, the daily volume would be 100 / 8.3 percent = 1,205 pedestrians. If the count interval was spread out over two periods, such as 9:30 a.m. to 10:30 a.m., then the adjustment factor for 9 a.m. to 10 a.m. was applied to the first part of the count, and the factor for 10 a.m. to 11 a.m. was applied to the second part of the count. Table 12. Adjustment factors by time of day and area type used to obtain estimated pedestrian ADT. Area Type Time of Day CBD (%) Fringe (%) Residential (%) 7 a.m. – 8 a.m. 2.4 6.9 4.8 8 a.m. – 9 a.m. 2.4 6.0 3.9 9 a.m. – 10 a.m. 4.9 8.3 5.7 10 a.m. – 11 a.m. 8.2 7.1 8.7 11 a.m. – 12 N 10.4 7.7 8.2 12 N – 1 p.m. 11.4 9.0 8.4 1 p.m. – 2 p.m. 11.6 6.3 6.9 2 p.m. – 3 p.m. 8.5 8.5 5.9 3 p.m. – 4 p.m. 16.2 8.1 7.4 4 p.m. – 5 p.m. 4.4 7.9 9.3 5 p.m. – 6 p.m. 3.5 8.1 11.4 Remaining 13 hours 16.0 16.0 19.5 At a few of the 2,000 sites, no pedestrians were observed during the crossing period. The pedestrian crash rate is computed as the number of pedestrian crashes divided by the pedestrian crossing volume. The pedestrian crossing volume is the product of the pedestrian ADT times the number of years times 365 days per year. Thus, assuming a zero hourly pedestrian volume is not only questionable, but also results in a pedestrian exposure of 0. Since it is not possible to use 0 as a value of exposure in computing pedestrian crash rates (i.e., since dividing by zero yields a rate of infinity), a count of 0.25 was substituted 67