Engineering judgment and road safety

Decisions that highway and traffic engineers make significantly affect the safety of road users. The documents that guide highway and traffic engineering practice suggest that many of these decisions be made by 'engineering judgment'. One would like this judgment to be informed by evidence-based anticipation of their likely safety consequences and by a professional ability to balance safety against mobility and other dimensions of 'utility'. I show that these desiderata are largely unfulfilled. The many implications of this finding are discussed.