This is what bicycle helmet laws achieve:

»The New Zealand helmet law (all ages) came into effect on 1 January 1994. It followed Australian helmet laws, introduced in 1990–1992. Pre-law (in 1990) cyclist deaths were nearly a quarter of pedestrians in number, but in 2006–09, the equivalent figure was near to 50% when adjusted for changes to hours cycled and walked. From 1988–91 to 2003–07, cyclists’ overall injury rate per hour increased by 20%. Dr Hillman, from the UK’s Policy Studies Institute, calculated that life years gained by cycling outweighed life years lost in accidents by 20 times. For the period 1989–1990 to 2006–2009, New Zealand survey data showed that average hours cycled per person reduced by 51%. This evaluation finds the helmet law has failed in aspects of promoting cycling, safety, health, accident compensation, environmental issues and civil liberties.«

(Colin F. Clarke:
Evaluation of New Zealand’s bicycle helmet law)