An increasing number of jurisdictions across the United States are exploring level of service (LOS) for multiple travel modes, in part due to the release of the 2010 Highway Capacity Manual (HCM 2010) as well as an increased focus on complete streets. One of the most important questions these jurisdictions are asking is whether new multimodal LOS (MMLOS) methods are sensitive enough to inform transportation investments, impact mitigation, or the prioritization of future projects. For this paper, transportation professionals (pubic, private, and academic) were surveyed about inputs they believed would have the greatest effect on pedestrian, bicycle, transit, and auto LOS or inputs they thought would have the greatest likelihood of being changed (i.e., to mitigate an impact or to improve existing conditions). Sensitivity testing was then performed at locations in four cities to measure how 2010 HCM MMLOS scores responded as these inputs were incrementally increased or decreased. While many inputs performed as expected, the testing also found cases where outputs were of a questionable direction or magnitude. The results of this study are informative for agencies considering adopting HCM 2010 MMLOS for purposes of mitigation, resource allocation, or strategic decision making. They also provide a starting point for additional research needed to enhance MMLOS methods.