The AASHTO Highway Safety Manual (HSM) is rapidly becoming a key safety management and evaluation tool for state and local highway agencies; MPOs; and the safety, design and traffic engineering professional community. The HSM was developed largely through NCHRP research and the First Edition was published in 2010. As the First Edition was being developed, it was clear that high-priority research could not be completed without delaying publication. An example is the safety prediction models for freeways and interchanges developed under NCHRP Project 17-45--while this research is important, the decision was made to publish the First Edition without this material. Several other research efforts to develop models for additional facility types for inclusion in the HSM are underway and, like the freeways and interchanges chapters, each are considered critical to increasing safety knowledge and practice. The HSM has fostered significant advances in analytical methods in highway safety and this evolution continues; with increased knowledge, Safety Performance Functions (SPFs) and Crash Modification Factors (CMFs) being developed on an ongoing basis. Users and researchers now have gained experience with the HSM and have outlined priorities for enhancements to HSM chapters, procedures, and models. An example of current research that could be included in the next edition is an FHWA decision tree used to determine whether to develop a state-specific safety performance function or to calibrate the functions provided in the HSM. Beyond applying the HSM in specific situations such as network screening, crash diagnosis and design exceptions, state departments of transportation and other users are developing their own safety performance functions, policies, agency-wide training programs and pursuing other implementation activities that more completely integrate the information in the HSM. With the implementation of the existing HSM, errors and misunderstanding of appropriate applications have been noted. With increasing knowledge and the growing experience of the HSM user, additional needs are continuing to be identified. These needs have led to a significant amount of combined research through NCHRP, FHWA, and pooled fund initiatives. This research is further developing and promoting the quantitative, data-driven approach to safety. These research efforts are not specifically developing new chapters for the HSM or enhancing models already in the manual, but are expected to result in advances that are suitable for inclusion in the next edition HSM or other AASHTO documents such as the AASHTO “Green Book.” Incorporating this material throughout the HSM will take specialized knowledge and research skills in order to appropriately identify, evaluate, refine and include this research in a manner suited to practitioners. The HSM Second Edition will represent an important advance in safety management and support the expanding evaluation capabilities of highway agencies.