Bridge width and road safety.  

Two great studies have been produced regarding the effects of bridge width on road safety. One by Mak and one by Corben Et. Al.
In summary, increasing the bridge width results in a significant reduction of crashes – 35%.  

In another study Zegeer and Council found that the difference between bridge and road width is related to crashes. Crashes increase as bridge width decreases.  

(in the photo you see Heathcote Road bridge, which is being upgraded for safety. Do the two different bridge width markers annoy us? Yes. Is it the major cause of crashes? No.)