https://doi.org/10.1177/0361198118755703 Transportation Research Record 2018, Vol. 2672(14) 20–28 © National Academy of Sciences: Transportation Research Board 2018 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0361198118755703 journals.sagepub.com/home/trr TRR JOURNAL OF THE TRANSPORTATION RESEARCH BOARD Article Managed lanes (MLs) are “designated (also defined as pref- erential) lanes and roadway facilities located on or adjacent to controlled-access urban/suburban metropolitan highways that are actively operated and managed to preserve opera- tional performance over comparable general traffic lanes” (1). Such preferential service often implies faster travel speeds and better reliability than on adjacent general-purpose (GP) lanes. Buffer separation and other geometric strategies can help to preserve these benefits. Recent research has found that higher speeds are associated with wider buffers (2). The wider ML buffer separation, travel lane, or shoulder width may also positively influence safety. Research Objectives To investigate the potential safety benefits, the Federal Highway Administration (FHWA) sponsored research (3) to determine the relationship between ML cross-section elements and crashes to evaluate the safety implications. This research examines different widths of the three key ML geometric elements: lane, buffer, and inner and outer shoulder. Access to and from a ML is assumed to affect safety so this research focused on the effects of the cross- section elements within a segment. Future research should attempt to quantify the relationship between crashes and ML access characteristics. Literature Review This section presents a summary of recent research for safety on freeways and on freeways with MLs. Safety on Freeways The Highway Safety Manual (HSM) includes crash predic- tion methods for freeways (4), and the research conducted as part of National Cooperative Highway Research Program (NCHRP) 17-45 formed the basis of the material in those chapters (5). The researchers found that reductions in lane widths and inside (left) shoulder widths are associated with increased crashes. The range of shoulder widths included in the NCHRP 17-45 study was 2–12 ft. An inside shoulder width of 6 ft was assumed as the base condition (6). A recent Texas Department of Transportation (TxDOT) project examined the trade-offs of reducing lane and shoul- der widths to permit an additional freeway lane and identi- fied increased crashes when the widths of lanes or shoulders 755703TRR XX X 10.1177/0361198118755703Transportation Research RecordAvelar and Fitzpatrick research-article 2018 1 Texas A&M Transportation Institute, College Station, TX Corresponding Author: Address correspondence to Raul E. Avelar: r-avelar@tamu.edu Safety Evaluation of Cross-Sectional Elements of Freeway Managed Lanes Raul E. Avelar 1 and Kay Fitzpatrick 1 Abstract This paper investigated the safety implications of managed-lane cross-sectional elements. The objective of the Federal Highway Administration project was to investigate the relationship between crashes and buffer-separated managed lane dimensions. The results from several previous research studies have demonstrated that reductions in freeway lane width or shoulder width are associated with more crashes. This research found that a narrower managed-lane envelope width (i.e., left shoulder, managed- lane, and buffer width combined) is also associated with more freeway crashes for crashes of all severity levels including fatal and injury. Wider envelopes are associated a reduction in total freeway crashes, of all severities, of 2.8% in Texas, and 2.0% in California, for each additional foot of envelope width. In California, wider envelopes are associated with a reduction of 4.4% in managed-lane-related crashes resulting in fatalities and injuries at all severity levels, for each additional foot of envelope width. The analysis was conducted on nonweaving managed-lane segments that included a single managed-lane separated from the general- purpose lanes with a flush buffer area. The dataset included crashes on 128.0 miles of freeway in California (all 128.0 miles with flush buffers) and 60.4 miles of freeway in Texas (41.7 miles with pylon buffers and 18.7 miles with flush buffers). The California sites included freeways with three or four general-purpose lanes, and the Texas freeways had three to five general-purpose lanes.