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## John Forester's comparison of bicycle usage (CPSC) vs. motor behicle usage (USDOT)## BICYCLE USAGEThe CPSC report gives the following statistics: Cyclists = 67 million Average hours/year/cyclist = 236 Adult cyclists = 33.5 million Average hours/year/adult cyclist = 134 [1]. The miles per warm-weather month of cyclists over the age of 17 is given as 34.4. If 8 months are used as the year this is 275 miles per year. If 12 months are used, this is 400 miles per year. Therefore: Cyclist hours per year = 1.58 x 10^10 Adult cyclist hours/year = 0.45 x 10^10 Child cyclist hours/year = 1.13 x 10^10 Average speed, adult cyclists 2 mph for 8 month year, 3 mph for 12 month year. The above is far too slow to be believable [2]. If we assume adult average speed is 10 mph, then the adult cyclist miles/year = 4.5 x 10^10. If we assume child cyclist average speed is 5 mph, then child cyclist miles/year = 5.7 x 10^10.
## MOTOR VEHICLE USAGEThe USDOT gives the following statistics: Automobiles = 144.2 million 2-axle, 4-tire trucks = 39.5 million Miles/year, autos = 11,000 2-axle trucks = 12,000 Therefore, average is 11,260 miles/year. At 30 mph this is 375 hours/year. Therefore: Motor-vehicle hours/year = 6.89 x 10^10 Motor-vehicle miles/year = 207 x 10^10 ## COMPARISONSThe above calculations say that: On an hours basis, bicycles ridden by children are 13% of the vehicles and bicycles ridden by adults are 5% of the vehicles[2]. Bicycles ridden by children produce 2.2% of the vehicle miles, and bicycles ridden by adults produce 2.7% of the vehicle miles[3]. Since bicycles are not used on interstates to any great extent, the above figures for bicycle proportions need to be amplified by dividing by the proportions of motorist time and miles that are done on interstates. I think that both the CPSC's figures for time spent are too high, and the figures for average miles/month (from Rodale) are too low, as shown by the absurd average speed calculations. The total probable error is approximately 5 times, which is sufficient to make the data useless. I have no estimate as to which factor is most erroneous. ## ENDNOTES1. I arrived at a somewhat higher figure of 182.4 hours, accounting for the variations among age groups. My calculations -- JSA. 2. The Rodale data show an average of less than 8 months of use, and the result is an even lower mph figure -- JSA] 3. Bicycles ridden by persons of unknown age are 0.6% of the vehicles. All bicycles are 18.7% of the vehicles. -- JSA 4. Bicycles ridden by persons of unknown age produce 0.2% of the vehicle miles and all bicycles produce 5.1% of the vehicle miles. Note that Forester's calculation accounts only for light motor vehicles, excluding heavy trucks, buses and motorcycles -- JSA |

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