Blame bad driving, not bad roads
This is really an opinion, not a statistic. One could equally say it is the failure of motorists to take into account road conditions, visibility, other traffic, etc, that causes crashes; the road can do nothing by itself.
What research has actually shown is that any improvements in safety, be it seat belts or better roads, are offset by motorists travelling at higher speeds and taking less care. This is known as risk compensation.