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55Â Â AADT Average annual daily traffic AASHTO American Association of State Highway and Transportation Officials ADT Average daily traffic C50 The 5-mph increment that is closest to the 50th percentile speed C85 The 5-mph increment that is closest to the 85th percentile speed CMF Crash modification factor Expanded FCS Expanded Functional Classification System FHWA Federal Highway Administration HSIS Highway Safety Information System HSM Highway Safety Manual ISW Inside shoulder width K Constant associated with the confidence level (1.645 for 95Â percent confidence) KABC Fatal and injury crash severity levels KABCO All crash severity levels LW Lane width M Exposure (100 million vehicle miles) mph Miles per hour MUTCD Manual on Uniform Traffic Control Devices MVM Million vehicle miles N Number of lanes NCHRP National Cooperative Highway Research Program NTSB National Transportation Safety Board Ra Average crash rate for a given road type, provided by the user or obtained from HSIS tables Rc Critical crash rate for a given road type RD50 The 5-mph increment obtained by rounding down the 50th percentile to the nearest 5-mph increment RD85 The 5-mph increment obtained by rounding down the 85th percentile to the nearest 5-mph increment SLS-Procedure Speed Limit Setting Procedure SLS-Tool Speed Limit Setting Tool SLSG Speed Limit Setting Group SW Shoulder width TCD Traffic control device TWLTL Two-way left-turn lane Acronyms and Abbreviations
