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Discussion about fees and taxes for bicycles so that we cyclists “pay our fair share” often turn to mentions of the “Fourth Power Rule.” What is this mysterious Fourth Power Rule?
Back in the 1950s and 1960s, highway engineers researched damage done to road beds and road surfaces for the purposes of allocating who should pay how much into the various road maintenance funds. The American Association of State Highway Ofﬁcials (AASHO; they added Transportation to their organization name during the 1973 OPEC oil embargo) collated this research and published their findings as a “Special Report” for a highway engineering conference in 1962.
What these researchers found is that damage to the roadbed is proportional to the 4th power of the axle load of the vehicle, and they called this “the Generalized Fourth Power Law.” This means that if you double the weight on an axle, your vehicle does sixteen times the damage to the road. The result is those signs you see on the backs of truck trailers that say “This truck paid $4,182 in highway taxes last year.”
Let’s take an example. A Toyota Prius weighs about 3,000 lbs, which is 1,500 lbs per axle. A Lincoln Navigator weighs in with a curb weight of 6,000 lbs, or 3,000 lbs per axle.
(3000 / 1500)4 = 24 = 16
Added on September 24, 2020 by Steven Edwards