The automatic crash notification system (ACNS) is a well-known technology with promising potential to reduce the crash response time (CRT) of emergency medical services. Reducing CRT will contribute to saving the lives of and alleviating the severity of injuries for crash victims. To fully operate the ACNS, it is important to quantify the safety benefits, which is fundamental for justifying public investment. This study proposed a methodology for quantifying the effectiveness of the ACNS and applied the methodology to the Korean freeway system. The proposed methodology consists of three steps. Fist, a statistical model was developed to predict injury severity using ordered logistic regression. Second, the amount of reduced CRT that would result from the ACNS was estimated. The effectiveness of the ACNS, which are defined as the number of reduced fatalities and severe injuries, were derived after considering the market penetration rate (MPR). When the proposed methodology is applied to 2010 freeway crash data, the result that fatalities are reduced by 11.8-18.1% when there is a 100% MPR. The outcomes of this study support decision making for public investments and for establishing relevant traffic safety policies.