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Appendix B: The Language of Traffic Engineering
<br />Research Brief — Volume No. 15
<br />Results
<br />85th Percentile Speed — Speed at which 85 percent of
<br />drivers are traveling at or below. Speed limits are typically
<br />set at the 85th percentile speed.
<br />95th Percentile Queue —The distance, generally measured
<br />in feet or number of vehicles, which will be exceeded in
<br />a lane, typically at an intersection, only five percent of the
<br />time. Usually used to help determine intersection turn lane
<br />lengths.
<br />Control Delay — The total amount of time a motorist takes
<br />to get through a road segment or intersection minus the
<br />time it would take without stopping due to traffic controls
<br />(like stop signs or traffic signals). Control delay includes
<br />decelerating and accelerating back to full driving speed.
<br />Functional Classification — the grouping of streets and
<br />highways into categories according to their characteristics
<br />and emphasis on mobility or access. Generally, categories
<br />include arterials (emphasizing mobility and fast travel), local
<br />roads (emphasizing access to adjoining properties), and
<br />collector roads (emphasizing a balance between the two
<br />and usually connecting arterials to local roads).
<br />Intersection Delay — The average amount of time, usually
<br />expressed in seconds, experienced by any vehicle traveling
<br />through an intersection.
<br />Level of Service (LOS) — Qualitative measure of traffic
<br />operations related to the amount of average delay
<br />experienced. Expressed in letter grades with LOS A
<br />representing the best operations with little to no delay and
<br />LOS F representing the worst operations with excessive
<br />delays and congestion.
<br />Measures of Effectiveness — Performance measures that
<br />define how well traffic is moving along a corridor or thru an
<br />intersection. The common MOEs are travel time, corridor
<br />speed, delay, and queues.
<br />Mitigation — Measures intended to reduce the impact of a
<br />development or improve an identified traffic issue by either
<br />improving capacity (like adding lanes) or reducing demand
<br />(like encouraging carpooling).
<br />Queue — Length of line of cars waiting at an intersection or
<br />at a bottleneck in a corridor, typically measured for each
<br />individual lane of traffic in feet or number of vehicles.
<br />Volume to Capacity (v/c) ratio — the number of vehicles
<br />through an intersection or roadway segment in a specific
<br />amount of time divided by the expected capacity of the
<br />road. Less than 1.0 indicates available capacity and above
<br />1.0 indicates more vehicles than can be accommodated.
<br />Typically, a v/c ratio above 0.85 suggests operational issues.
<br />Trip Generation — The amount of vehicle traffic generated
<br />by a land use. One trip is equal to one vehicle traveling from
<br />an origin to a destination (traveling to and from work equals
<br />two trips).
<br />Warrants — Criteria based on volumes and other Measures
<br />of Effectiveness for determining when all way stop signs,
<br />roundabouts, traffic signals, or other type of control should
<br />be installed.
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<br />About This Brief
<br />Spack Consulting prepared this brief as part of our company's vision to significantly improve the practice of traffic engineering
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<br />CONSULTING
<br />Traffic Impact Study Capstone Homes Residential Development B2
<br />Mike n S PAC K
<br />traffic ACADEMY
<br />r
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<br />YI
<br />TRAFFIC DATA INC.
<br />Spack Consulting
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