AADT (Annual Average Daily Traffic) – the total volume of traffic passing a point or segment of a highway in both directions for one year divided by the number of days in the year

AM peak – the morning time period when traffic volumes are highest; also referred to as “morning rush hour”; it can often be more than 60 minutes in length; typically falls between 7:00 and 9:00AM in the Pittsburgh region

average speed – the length of a highway segment divided by the time it takes to traverse that segment, including all delays

before and after study – a study undertaken to determine the effects of an implemented project, program, or policy change; performance measures are assessed before and after implementation to measure impacts; costs can also be taken into account and compared to benefits in order to gauge cost-effectiveness of the solution

CMP (Congestion Management Process) – a federally mandated program within metropolitan planning areas to address and manage congestion; formerly known as a Congestion Management System (CMS)

CMS (Congestion Management System) – prior to SAFETEA-LU, CMP was referred to as CMS

congestion – the level at which transportation system performance is no longer acceptable due to traffic interference. The level of system performance deemed acceptable by State and local officials may vary by type of transportation facility, geographic location (metropolitan area or subarea, rural area), and/or time of day (23 C.F.R. § 500.109)

crash rate – the frequency with which traffic accidents have occured along a defined roadway segment over a defined period of time

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delay – the amount of time it takes to traverse a given roadway segment minus the amount of time it would take to traverse that roadway segment at the posted speed limit if there were no interference

Delay per Vehicle – see “delay”

Delay per Vehicle per Mile – Delay per Vehicle divided by the length of the roadway segment; this performance measure is used to facilitate the comparison of unequal roadway segments

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HOV (high-occupancy vehicle) lanes – roadway lanes that are restricted for use by vehicles carrying a designated number of passengers (above 1) during peak times of the day

HOT (high-occupancy toll) lanes – roadway lanes that charge a fee during peak times of the day for vehicles not carrying a designated number of passengers (above 1)

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ideal travel time – the amount of time it would take to traverse a given roadway segment at the posted speed limit if there were no interference

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Level of Service (LOS) – a qualitative measure describing operational conditions within a traffic stream, based on service measures such as speed and travel time, freedom to maneuver, traffic interruptions, comfort, and convenience; can be calculated for roadway segments, intersections, merges, diverges, weaving areas, and other roadway features

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minor arterial – a functional category of a street allowing trips of moderate length within a relatively small geographic area

node – a defined point along a roadway corridor that marks the beginning and/or end of a segment

non-recurring congestion – congestion related to short-term or temporary occurrences; examples include special event traffic, construction, and traffic accidents

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PDO (Property Damage Only) crash – a reportable crash that did not result in any fatalities or notable injuries

peak hour volume – the volume of traffic passing a point or segment of a highway during the busiest hour of a typical day

performance measures – objective measurements and observations to determine the degree of success a project, program, or initiative has had in achieving its stated goals and objectives

PM peak – the afternoon/evening time period when traffic volumes are highest; also referred to as “evening rush hour”; it can often be more than 60 minutes in length; typically falls between 4:00 and 6:00PM in the Pittsburgh region

principal arterial – a major surface street with relatively long trips between major points and with through-trips entering, leaving, and passing through an urban area

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qualitative – involving distinctions based on qualities rather than something that can be measured with numbers

quantitative – involving distinctions based on measurements

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recurring congestion – the level of congestion that results from typical daily traffic volumes and travel patterns

reportable crash – a traffic accident where someone was injured or where one of the vehicles had to be towed from the scene

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SAFETEA-LU (Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users) – federal legislation authorizing highway, safety, transit and other surface transportation programs from 2005 through 2009; maintained many initiatives from ISTEA and TEA-21 with increased emphasis on certain areas such as highway safety

segment – the portion of a highway corridor between two defined points

severity index – a weighted measure of the relative economic cost to society of the injuries and fatalities related to traffic crashes along a defined roadway segment [ disclaimer ]

SOVCAP (Single Occupancy Vehicle Capacity Adding Project) – a transportation project which significantly increases the carrying capacity of a roadway. This includes new facilities (a new roadway or bypass, a new interchange, ramps that add missing moves at a previously incomplete interchange, an access road, new bridge, or new connector) or the addition of new, general-purpose lanes to an existing facility. Exempt from this definition, and consequently exempt from CMP review, is any project that adds less than one lane-mile of general-purpose roadway. Also exempt are realignments which replace rather than supplement previous roadways for through traffic, turning lanes, acceleration/deceleration lanes, climbing lanes, bridge replacements, widening without adding new travel lanes, and facilities that are primarily for use by modes other than SOVs (such as bus lanes, HOV lanes, truck lanes, and bicycle and pedestrian facilities). In areas that are considered to be in non-attainment for air quality, a SOVCAP may not receive federal funding beyond the preliminary engineering phase unless consistency with the regional CMP has been demonstrated 

spot speed – the speed of a vehicle at a particular moment in time; different from average speed because it is a snapshot of a particular moment rather than speed over a certain distance

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Total Delay – Delay per Vehicle multiplied by the peak hour volume in that roadway segment; expressed in vehicle-hours; this performance measure facilitates the comparison of corridors by considering the number of vehicles impacted by the congestion (e.g., Corridor A and Corridor B both have 5 minutes of delay per vehicle; however, Corridor A impacts 100 vehicles and Corridor B impacts 1,000 vehicles, suggesting Corridor B is a more significant problem)

Total Delay per Mile – Total Delay divided by the length of the roadway segment; this performance measure is used to facilitate the comparison of unequal roadway segments and corridors

TDM (travel demand management) – programs and initiatives that attempt to address congestion by reducing the number of vehicles on the road

travel time – the amount of time, measured in the field, that it takes to traverse a given roadway segment

“typical day” – a weekday that exhibits travel patterns which occur on a regular basis; standard practice is to collect data on Tuesdays, Wednesdays, and Thursdays of weeks without holidays or other occurrences that may influence travel patterns

typical park-n-ride utilization – the average usage level of park-n-ride lots serving a given corridor on a typical day; usage can vary considerably between lots based on a variety of factors such as transit availability

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v/c ratio – volume-to-capacity ratio is a measure of the amount of traffic on a given roadway in relation to the amount of traffic the roadway was designed to handle

vehicle-hour – equivalent to one vehicle delayed for one hour

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For more information about our Congestion Management Process, contact Doug Smith at (412) 391-5590 x327 or e-mail dsmith@spcregion.org.

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