Note that the first speed bump at the top of One Tree Hill is particularly vicious, and I suspect above the 10cm height guideline.

The subsequent bumps towards HOP are lesser in height, and probably within guidelines.

If the bumps alone are not working to deter speeding motorists, another approach should be taken as raising the bumps would be illegal.

More bumps should not be encouraged due to the increase in noise, and emissions pollution that they create.

Thanks to gravity, things always roll down hills faster than on the flat, so maybe we can put in a proposal to level One Tree Hill.... It's a swine to cycle over.