The law is truly an ass.
No it isn't, unlike the legislators you simply haven't considered all the relevant factors.
Power assistance is allowed on bicycles for those who need it, not as a general provision to increase performance. The legislation is therefore aimed at utility cyclists who tend to cycle at under 15 mph, more commonly at around 10 to 12 mph. Lycras who ride at over 20 mph are completely irrelevant, clearly they do not need assistance.
Some safety laws are needed since unlike the operators of other powered vehicles, e-bikers are not tested in any way for proficiency. These laws and the reasons for them are as follows:
Assist speed limited to 25 kph/15.5 mph. This emphasises the need over performance factor, but more importantly it's connected to the fact of no rider proficiency testing. Physical fitness, reaction times, eyesight and hearing are broadly connected, we can be reasonably confident that the fit lycra clad rider is overall fairly safe at over 15 mph in these respects. The utility riders who the e-bikes are intended for are often going to be elderly with those facilities often impaired in many ways. They can often be partially disabled with impairments affecting safety. In the absence of rider testing the safety of the public at large has to take precedence.
Connected with the level at which the assist speed limit is set is the effect that evolution has had on our abilities. A fit normal person can run at up to 18 mph, so evolution has developed our senses and reactions to cope best with speeds up to that. As mentioned though, those senses and reaction times deteriorate with age, so given the target group likely common age profile, the assist speed is set a bit lower. Originally in Britain it was set at 12 mph but this was later raised to 15 mph to give some parity with EU law while still being lower than the optimum for the fully fit.
Pedelec control. This is to emphasise that the e-bike remains a bicycle with the power applied by pedalling, not a low powered motor cycle. That is why the EU don't allow throttles at all assist speeds.
To summarise, bureaucracy free pedelec law is not daft or irrational, and those who feel it is simply haven't considered all the relevant factors.
For those who want higher speeds there is another bicycle based class with some added bureaucracy for safety reasons, the S class, but to date our DfT will not permit it. That is where any lobbying should be directed, not at changing pedelec law, probably getting extra restrictions added and inconveniencing all.
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