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Appendix B: The Language of Traffic Engineering - Volume No. 15 Results 85th Percentile Speed — Speed at which 85 percent of Queue— Length of line of cars waiting at an intersection or drivers are traveling at or below. Speed limits are typically at a bottleneck in a corridor, typically measured for each set at the 85th percentile speed. individual lane of traffic in feet or number of vehicles. 95th Percentile Queue—The distance, generally measured Volume to Capacity (v/c) ratio — the number of vehicles in feet or number of vehicles, which will be exceeded in through an intersection or roadway segment in a specific a lane, typically at an intersection, only five percent of the amount of time divided by the expected capacity of the time. Usually used to help determine intersection turn lane road. Less than 1.0 indicates available capacity and above lengths. 1.0 indicates more vehicles than can be accommodated. Control Delay—The total amount of time a motorist takes Typically,a v/c ratio above 0.85 suggests operational issues. to get through a road segment or intersection minus the Trip Generation —The amount of vehicle traffic generated time it would take without stopping due to traffic controls by a land use. One trip is equal to one vehicle traveling from (like stop signs or traffic signals). Control delay includes an origin to a destination (traveling to and from work equals decelerating and accelerating back to full driving speed. two trips). Functional Classification — the grouping of streets and Warrants—Criteria based on volumes and other Measures highways into categories according to their characteristics of Effectiveness for determining when all way stop signs, and emphasis on mobility or access. Generally, categories roundabouts, traffic signals, or other type of control should include arterials(emphasizing mobility and fast travel), local be installed. roads (emphasizing access to adjoining properties), and collector roads (emphasizing a balance between the two and usually connecting arterials to local roads). Intersection Delay—The average amount of time, usually Important Manuals/Guides expressed in seconds, experienced by any vehicle traveling through an intersection. HCM—Highway Capacity Manual(released by the Transportation Research Board,or TRB).The guide for Level of Service (LOS) — Qualitative measure of traffic engineers and planners to assess traffic and environmental operations related to the amount of average delay effects of highway projects.This manual presents the experienced. Expressed in letter grades with LOS A foundation of traffic analysis procedures in the US. representing the best operations with little to no delay and LOS F representing the worst operations with excessive MUTCD—Manual of Uniform Traffic Control Devices. delays and congestion. A document that sets minimum standards and provides Measures of Effectiveness — Performance measures that guidance to ensure uniformity of traffic control devices(such define how well traffic is moving along a corridor or thru an as messages,location,size,shapes,and colors)across the intersection. The common MOEs are travel time, corridor nation.All roads are subject to its jurisdiction. speed, delay, and queues. Mitigation — Measures intended to reduce the impact of a HSM—Highway Safety Manual (released by AASHTO). development or improve an identified traffic issue by either A guide that presents a variety of methods for quantitatively improving capacity (like adding lanes) or reducing demand estimating crash frequency or severity. (like encouraging carpooling). Resources Highway Capacity Manual, HCM2010 MUTCD, 2009 Edition, published by FH WA Highway Safety Manual, HSM About This Brief Spack Consulting prepared this brief as part of our company's vision to significantly improve the practice of traffic engineering and transportation planning. Transportation professionals from around the world have assisted us in developing this document. We are providing this brief under the Creative Commons Attribution License. Feel free to use-modify-share this guide, but please give us some credit in your document. To request our whole series of Design Briefs and to be included on our distribution list for new materials, please email mspack@spackconsulting.com. And please reach out if you have any comments or questions related to this Design Brief. em Mike n S PACK COUN-irING traff � Ccirs.corn V� CONSULTING ACADEMY TRAFFIC DATA INC. Traffic Impact Study Pearson Farm Residential Development 132 Spack Consulting