There is currently no commonly accepted or adopted measure of pedestrian and bicycle exposure to risk. Consequently, a large portion of the field of pedestrian and bicycle safety is lacking an adequate means to evaluate the effectiveness of its efforts. The current study presents a proposed metric for measuring pedestrian and bicycle exposure to risk: hundred million pedestrian or bicycle miles of roadway (or other motor vehicle shared facility) traveled. A method for implementing the proposed exposure metric is described for eight shared-facility types characteristic of the urban environment of Washington, D.C. These facilities include three types of intersections, midblock road segments, driveways, alleys, parking lots, parking garages, school areas, and areas with playing, dashing, and working in the roadway. The methodology is then used to calculate the annual pedestrian and bicycle exposure for the city for the calendar year 2007. The results of these calculations revealed 0.82 hundred million miles for pedestrian exposure and 0.37 hundred million miles for bicyclist exposure. In this way both the feasibility and scalability of the proposed metric were successfully demonstrated for a relatively large urban environment. Thus the proposed metric has the potential to eliminate one of the major obstacles in the pedestrian and bicycle safety field, the lack of adequate exposure data. Although further refinement and validation are still needed, the proposed metric provides a possible initial foundation to develop a national unit of risk exposure for pedestrians and bicyclists.

Subjects (14 high-school students) made judgments of equal loudness by adjusting the intensity of comparison tones of ten different frequencies. The comparison tones were presented diotically alternately with standard tones (1-sec duration each). Each standard tone remained fixed at one frequency (125, 1000, or 8000 Hz) and one intensity (10, 20, 40, or 70 dB sensation level) while the data were collected for any single equal loudness contour. In this manner, families of equal loudness contours were generated for each of the three standard frequencies. The contours at 1000 Hz were compared with those for 1000 Hz in the literature. The contours for 125 and 8000 Hz, determined by otherwise using the same algorithm, were different in shape from the 1000-Hz set as well as from each other. These differences implied a violation of the transitivity assumption in the loudness calculating algorithm. Tests for transitivity among the three standard frequencies failed in many cases.

A modification is proposed in Hirsch's equation for determining the range of a sound source of unknown strength [H. R. Hirsch, J. Acoust. Soc. Am. 43, 373–374 (1968)]. The modified formula applies to the case where the direction of the sound source is known. Greene's comments on Hirsch's letter are investigated for their ability to predict the limitations on the resolution obtainable in human auditory ranging [D. C. Greene, J. Acoust. Soc. Am. 44, 634 (1968)]. In a brief experiment, two subjects were unable to make distance judgments for sustained pure-tone sources over ranges of 3 to 48 ft.

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