NHTSA reported that in 2006, 9.8% of fatal crashes and 4.1% of injury crashes were head-on crashes (Traffic Safety Facts 2006). Honda has developed a pre-production Head-on Collision Avoidance Assistance System (H-CAAS) intended to detect, warn and mitigate specific crash types, including a severe, primary crash type in which the subject vehicle drifts laterally into the path of an on-coming vehicle, typically as a result of driver inattention (due to, e.g., distraction, drowsiness or alcohol impairment). The goal of this research is to estimate H-CAAS safety benefits, at a national level, focusing on both primary and secondary technology relevant crash types (TRCT’s). This paper provides a progress report on the evaluation of US-level safety benefits of H-CAAS, based on the Safety Impact Methodology (SIM) tool developed by Honda and DRI and extended under Cooperative Agreements with NHTSA, as well as a description of recent extensions of the SIM itself. The SIM developed by Honda and DRI applies computer simulations of the drivervehicle- environment, involving time-space relationships between the subject vehicle and a collision partner, and predicts crash, injury and fatality outcomes, with and without the Advanced Collision Avoidance Technology (ACAT) countermeasure, for a sample of NASS/CDS cases;​ and a systems model to extend the sample results to the national level, in order to estimate effectiveness and safety benefits of the countermeasure in terms of crash, injury, and fatality reductions. Data sources include NHTSA FARS, NASS/CDS, GES, and PCDS accident data;​ vehicle parameter and exposure data (e.g., from Polk vehicle registration data);​ and countermeasure-specific data from objective tests. For the H-CAAS evaluation, results from previous driving simulator objective tests involving n=9 distracted drivers and n=10 drowsy drivers were used to parameterize, calibrate and validate the SIM tool. The SIM was then used to estimate US-level safety benefits of H-CAAS. Results of extending the SIM include the addition of a simplified head-on accident reconstruction module which takes into account the generally large closing speeds, approximately 180 degree relative heading angles and the relatively small lateral offsets and drift rates of sampled headon crashes;​ and substantial upgrades of the Guided Soft Target collision partner test system, in terms of a more realistic 2nd generation soft body and greater operating speed and range. The extensions to the SIM have resulted in a more robust, accurate and widely applicable suite of tools for estimating safety benefits of advanced safety technologies at a national level. A limitation of the SIM tool is that the uncertainty bounds associated with the estimates include some but not all sources of uncertainty.