Dunno. The ones introduced on Silverdale two or three years ago - the money could have been better used otherwise considering how ineffective they are for slowing traffic, but IIRC road-budget can't be transferred to say lousy pavements so maybe the council is just trying to use up their fiscal year's road budget? Bumps have to be a regulation height given how many times people have claimed for damage to undercarriage if bumps are too high - maybe they were too high...