The construction of highway bypasses raises economic and safety concerns among citizens of bypassed communities. This thesis describes the use of a full Bayesian analysis to evaluate the impact of bypasses on traffic safety. Traffic safety has been assessed for the periods before and after the construction of the bypass both on the old road network consisting of the main road through town and on the new road network consisting of the main road and the bypass. Furthermore traffic safety has been assessed for all travelers through or around the communities and then for local citizens of the communities only.;The results suggest that overall crash frequencies and rates decrease, however, the rate of crashes involving citizens of the bypassed communities increases on the main road. The reduction in traffic volume may be affecting the rates of crashes involving local citizens.