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Publications: Glossary of Transportation Terms

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

A

Arterial

A major thoroughfare.

Automated Vehicle Identification (AVI) System

or Automatic Vehicle Monitoring System or Automatic Vehicle Location System. A system in which electronic equipment on a vehicle sends signals back to a central control facility, locating the vehicle and providing other information about its operations or about its mechanical condition. AVI is also referred to as Automatic Vehicle Monitoring System and Automatic Vehicle Location System.

Average Annual Daily Traffic (AADT)

The total traffic for a year divided by 365.

Average Daily Traffic

The total traffic volume during a given period (from 1 to 364 days) divided by the number of days in that period. Current ADT volumes can be determined by continuous traffic counts or periodic counts. Where only periodic traffic counts are taken, ADT volume can be established by applying correction factors such as for season or day of week. For roadways having traffic in two directions, the ADT includes traffic in both directions unless specified otherwise.

Average Weekday Daily Traffic (AWDT)

The total traffic for an average weekday. An average weekday is a representative weekday computed as the mathematical average of several typical weekdays selected at random throughout the year. A typical weekday has no anomaly such as heavy traffic due to a special public event or light traffic due to inclement weather. Average Saturday and Sunday data, including holiday service, are determined the same way.

B

Benefit/Cost (B/C) ratio

B/C is used to compare the benefit versus the cost of proposed alternatives. For highway projects, benefits may include reduced fuel consumption, travel time, and air pollution; costs may include construction, right of way, and maintenance.

Bottleneck

Highway sections that experience operational problems such as congestion. Bottlenecks may result from factors other than reduced roadway width. For example, the close spacing of exit and entrance ramps can cause weaving patterns that result in congestion. A less obvious example is a steep freeway grade that can slow trucks and cause a localized "bottleneck."

C

Capital Area Metropolitan Planning Organization (CAMPO) (formerly ATS)

CAMPO is the Metropolitan Planning Organization (MPO) for the Austin area.

Capacity

Capacity refers to a rate of vehicular or person flow that can be expected to traverse a point or uniform section of a lane or roadway during a specific period, which is most often a peak 15-minute period, and which is not the maximum volume that can be accommodated during an hour, under prevailing roadway, traffic, and control conditions. Capacity and Level of Service (LOS) are analyzed separately and are not simply related to each other; both must be fully considered to evaluate the overall operation of a facility. Capacity analysis may be used in the computation of Volume-to-Capacity (V/C) ratios. In some cases, the V/C ratio is used to define LOS.

Categorical Exclusion

Examples of categorical exclusions are actions which, based on past experience with similar actions, do not involve significant environmental impacts. They are actions which do not do any of the following: induce significant impacts to planned growth or land use for the area; require the relocation of significant numbers of people; have a significant impact on any natural, cultural, recreational, historic or other resource; involve significant air, noise, or water quality impacts; have significant impacts on travel patterns; or otherwise, either individually or cumulatively, have any significant environmental impacts.

Central Business District (CBD)

The downtown retail trade and commercial area of a city or an area having high land values, traffic flow, and concentration of retail business offices, entertainment, lodging, and services.

Changeable Message Sign (CMS)

A CMS is used to advise drivers of traffic or roadway conditions ahead and, in some cases, recommend alternate routes. The CMS also reduces driver frustration by providing advance warning. A CMS is also referred to as a Variable Message Sign (VMS).

Collector Distributor (CD)

A CD freeway system separates local and through traffic by use of CD roadways and through roadways ("main lanes" or "core roadway"). The CD roadway is located between the main lanes and a frontage road or local street system. On the main lanes, traffic flow is improved since weaving is eliminated and access points are reduced; the CD roadway provides needed freeway access points. A CD roadway is different from a frontage road because access to adjacent properties is not permitted. A CD roadway can complement an existing frontage road system by inclusion of ramps connecting the CD roadway to the frontage road; the frontage road is then better able to handle traffic accessing adjacent properties. For traffic traveling between a freeway system and more distant points, "direct connect" ramps can be used to "directly connect" the CD roadway to major thoroughfares (leading to major traffic generation areas) and, thereby, bypass frontage roads or local streets adjacent to the freeway. This CD roadway and direct connect ramp arrangement eliminates merging and weaving movements that would otherwise occur between the freeway, frontage road, and local roads. During peak traffic, this arrangement can provide the added benefit of keeping open those sections of freeway lanes approaching exit ramps since greater storage length for exiting traffic queues (lines of vehicles waiting their turn) is made; increased queue storage is made by the greater length of the direct connect ramps, the reduction of turbulence in the queue (no access to adjacent property), and the relocation of the queue away from, instead of parallel with the freeway. A CD system with direct connect ramps can promote intermodalism since it provides for easier movement of transit vehicles like buses. Buses can easily travel directly between the CD roadway and local streets without having to merge and weave on and off of frontage roads. The CD roadway's operating speed is generally lower than the main lanes since the CD roadway has more entrance and exit areas. It is worth noting that a freeway's optimal traffic carrying capacity occurs at around 45 mph. Because of this lower operating speed, the CD roadway may be designed with a lower design speed which allows for more flexible design. In general, a freeway system with high traffic volumes, in a city-type area, can have its overall traffic carrying capacity and flow operations improved by use of a CD system. CD systems are currently in operation in several cities across the nation.

Commuter Rail (CR)

Commuter Rail is urban passenger train service for short distance (local) travel between a central city and adjacent suburbs and long haul (regional) passenger service between cities. It does not include heavy rail service or light rail service (serving longer distances). Commuter rail service may be either locomotive-hauled or self-propelled, and is characterized by reduced fare multi-trip tickets, specific station-to-station fares, railroad employment practices, and usually only one or two stations in the central business district. Also known as "suburban rail." It may cross the geographical boundaries of a state.

Congestion/Demand Management (CDM)

See Transportation Demand Management and Congestion Management System.

Congestion Management System (CMS)

A systematic process which provides information on transportation system performance and alternative strategies to alleviate congestion and enhance the mobility of persons and goods. A CMS includes methods to monitor and evaluate performance, identify alternative actions, access and implement cost-effective actions, and evaluate the effectiveness of implemented actions.

Congestion Mitigation and Air Quality (CMAQ) improvement program

A special provision of the ISTEA that directs funds towards projects in Clean Air Act Non-Attainment areas for ozone and carbon monoxide.

Congestion Pricing

The policy of charging drivers a fee that varies with the level of traffic on a congested roadway. Congestion pricing is designed to allocate roadway space in a more efficient manner. Congestion pricing is also known as relief tolling, variable pricing, and road pricing.

Control of Access (COA)

This is also referred to as access control. COA is the regulated limitation of access and is achieved by regulation of public access rights into (ingress) and out of (egress) properties abutting a roadway. There are two types: full control of access and partial control of access. Also, there are driveway and approach control regulations. On a roadway with full COA, preference is given to the movement of through traffic by providing access connections only with selected public roads, by prohibiting crossings at the same grade, and by prohibiting direct private driveway connections. On a roadway with partial COA, preference is given to through traffic; however there may be access connections with selected public roads, crossings at the same grade, and private driveway connections. Full or partial access control is usually accomplished by legally obtaining right-of-access from the abutting property owners or by the use of frontage roads.

Critical Movement Analysis (CMA)

For signalized intersections, CMA focuses on lane groups or movements which control signal requirements. CMA focuses on the identification and provision of capacity for such flows called critical movements. CMA is also used in capacity analysis.

D

Design Hour Volume (DHV)

Typically, the DHV is the thirtieth highest hourly traffic volume for the design year, commonly twenty years from the time of construction. The DHV is given in units of vehicles per hour.

Directional Design Hour Volume (DDHV)

Typically, the DDHV is the thirtieth highest hourly traffic volume in one direction for the design year, commonly twenty years from the time of construction. DDHV is given in units of vehicles per hour.

Draft Environmental Impact Statement (DEIS)

An environmental document that is prepared when it is initially determined that the action/project may cause significant impacts to the environment, when environmental studies and early coordination indicate significant impacts, or when review of the environmental assessment indicates that the impacts anticipated to result from the project may be significant. The DEIS compares all reasonable alternatives to the proposed project and summarizes the studies, reviews, consultations, and coordination required by legislation and Executive Orders to the extent appropriate at the draft stage in the environmental process. This document lists all entities from which comments are being requested.

E

Environmental Assessment (EA)

A document that assesses an action that is not a categorical exclusion and does not clearly require the preparation of an environmental impact statement (EIS), or where the Federal Highway Administration believes an environmental assessment would assist in determining the need for an EIS.

Environmental Impact Statement (EIS)

An environmental document that is required when an action that will significantly affect the environment.

Environmental Protection Agency (EPA)

A Federal agency charged with protecting the natural resources on the nation.

Expressway

An expressway is a divided highway facility usually having two or more lanes for the exclusive use of traffic in each direction and partial control of access (as opposed to a freeway which has full control of access).

F

Feasibility Study

A study about a project's feasibility which is summarized in a document. The study addresses issues including the project's benefits, costs, effectiveness, alternatives considered, analysis of alternative selection, environmental effects, public opinions, and other factors. The feasibility study for major projects involving Federal funds was replaced under the Intermodal Surface Transportation Efficiency Act by the Major Investment Study.

Federal Highway Administration (FHWA)

The federal agency responsible for the administration of federal highway funds. FHWA does not have a direct role or responsibilities in the development of urban transportation plans or their development. However, their role is administration of federal funds and in the issuance of policy and procedure timetables for implementation of federal legislative directives is immense.

Federal Transit Administration (FTA)

The FTA was formerly as the Urban Mass Transportation Administration. It operates under the authority of the Federal Transit Act. The FTA was established as a component of the US Department of Transportation.

Final Environmental Impact Statement (FEIS)

An environmental document that is prepared following the Draft Environmental Impact Statement (DEIS), which includes the results of the public involvement process and agency input on the DEIS. This document summarizes the substantive comments on social, economic, environmental, and engineering issues made as a result of the public involvement process, and documents compliance with requirements of all applicable environmental laws, Executive Orders, and other related requirements.

Flexible Operational Capability

Allows the direction of lanes to change to accommodate uneven traffic flow. For example, during an evacuation, 7 northbound lanes can be created for evacuees and 1 southbound lane for emergency vehicles.

Freeway

A divided highway facility having two or more lanes for the exclusive use of traffic in each direction and full control of access. The freeway is the only type of highway intended to provide complete "uninterrupted" flow.

Frontage road

An arterial type roadway that parallels a major transportation facility such as a freeway. It serves to collect and distribute traffic along the major facility without impeding flow along the freeway. Frontage roads are also referred to by the public as "access," "feeder," and "service" roads.

G

Grade

The slope (ratio of change in elevation to change in distance) of a roadway typically given in percent. For example, a 2% grade represents 2-feet of elevation change over a 100-foot distance.

Grade Separation

A vertical separation between intersecting roads or railroad tracks. One facility travels over the other via an overpass or other structure.

H

High Occupancy Vehicle (HOV)

Vehicles having more than one occupant. Examples include carpools, vanpools, buses, and mini-buses. Transportation systems may encourage HOV use by having designated HOV lanes.

High Occupancy Vehicle (HOV) Lane

High Occupancy Vehicle Lane. Exclusive road or traffic lane limited to buses, vanpools, carpools, emergency vehicles, and in some cases, single occupant motorcycles. HOV lanes typically have higher operating speeds and lower traffic volumes than adjacent general purpose lanes. HOV lanes have proven to be successful in major metropolitan areas across the US; however, their full effectiveness is usually not realized until about one to two years after implementation.

High Speed Rail

A rail service having the characteristics of intercity rail service which operates primarily on a dedicated guideway or track not used, for the most part, by freight, including, but not limited to, trains on welded rail, magnetically levitated (MAGLEV) vehicles on a special guideway, or other advanced technology vehicles, designed to travel at speeds in excess of those possible on other types of railroads. High Speed Rail has exclusive right of way and serves densely traveled corridors at speeds of 124 miles per hour and greater.

Highway Advisory Radio (HAR)

A radio station which broadcasts highway conditions and traffic information.

Hourly Volume (HV)

The volume of traffic (given in units of vehicle per hour) that traverses across a segment of a roadway in one hour. The HV may be determined from traffic counts or may be a projected calculation. Refer to Design Hour Volume.

I

Incident

An incident may be any of the following: traffic accident, stalled vehicle, load spillage, or other action that effects one or more lanes of traffic. An "accident" typically involves a collision of a moving vehicle with another vehicle, person, or object.

Intelligent Transportation System (ITS)

ITS replaces the term Intelligent Vehicle Highway System. ITS is a surveillance system designed to monitor traffic flows on major freeways and to inform motorists or problem areas. Some ITS technology includes changeable message signs, cameras, and video detectors. ITS applications include: the integration of traffic control and transportation management systems; traffic signals which adapt to traffic and change control each cycle; highway advisory radio systems; changeable message signs (CMS); vehicle detectors; closed-circuit television; Global Positioning Systems and route guidance (currently used in some trucks, buses, and rental cars). An ITS may enable drivers to operate their vehicles more safely and with greater knowledge about existing traffic conditions.

Intelligent Vehicle Highway Systems (IVHS)

See Intelligent Transportation System.

Intermodal Surface Transportation Efficiency Act (ISTEA)

A Transportation Bill passed by Congress in 1991 that provides six year authorizations for development of a National Intermodal Transportation System which consists of all forms of transportation in a unified, interconnected manner. It increased the percentage of federal match funding available for the majority of Texas transportation projects. ISTEA was designed to move goods and people more efficiently by developing an integrated transportation infrastructure system for the United States. ISTEA is this country's first serious effort to promote intermodalism, the idea that all systems and structures for moving people and goods must function as an integrated and cohesive transportation network which includes rail and mass transit as well as highways. Under ISTEA, the statewide planning process must incorporate some new goals: to reduce congestion and improve air quality; to consider national and international commerce; to consider energy conservation; to create an integrated system of several modes; and to concentrate on the most efficient way to move goods and people, not just people. The three major components of ISTEA are the National Highway System, the Surface Transportation Program, and the Congestion Mitigation and Air Quality Improvement Program.

Intermodal Transportation

Transportation of persons and goods that involves the interchange between transportation modes such as surface routes, airways, and waterways. Intermodal transportation for surface transportation of people and goods includes the interchange between modes such as automobiles, mass transit such as buses, railway including commuter rail and can include Park And Ride lots or other mode interchange facilities. Intermodal transportation enables people and goods to be consolidated into larger groups that can be transported at lower costs. In addition to reducing costs, it enables greater logistic flexibility than can also reduce congestion and travel time.

Intermodalism

A holistic view of transportation in which individual modes work together or within their own niches to provide the user with the best choices of service, and in which the consequences on all modes of policies for a single mode are considered. This view has been called balanced, integrated, or comprehensive transportation. Intermodalism includes the provision of connections between different modes, such as highways to bus feeder services to rail transit.

K

K-Factor

A factor which represents the proportion of Average Annual Daily Traffic (AADT) expected to occur in the design hour. The K-factor is also known as the design hour factor and is normally expressed in design problems as DHV=AADT x K, where the DHV is the total two-way Design Hour Volume, and K is estimated from the ratio of the 30th Hourly Volume to the AADT from a similar site.

L

Level Of Service (LOS)

A qualitative measure describing operational conditions within a traffic stream and motorists' perceptions of those conditions. For example, LOS A represents free flow, almost complete freedom to maneuver within the traffic stream. LOS F represents forced flow, more vehicles are attempting to use the freeway than can be served resulting in stop and go traffic.

Light Rail Transit (LRT) or Light Rail

A railway with a "light volume" traffic capacity compared to "heavy rail." Light rail may use shared or exclusive rights of way, high or low platform loading, and multi-car trains or single cars traveling on fixed rails. LRT uses lightweight, streetcar type passenger vehicles operated on city streets that is not separated from other traffic for much of the way. LRT also known as light rail, streetcar, trolley car, and tramway.

M

Major Investment Study (MIS)

A study and resulting document which replaced Feasibility Studies under the Intermodal Surface Transportation Efficiency Act (ISTEA) for major improvement projects involving significant Federal funds. A MIS includes the study of factors that may justify a proposed project such as it's cost effectiveness and overall effectiveness and incorporation of intermodal transportation. Measures Of Effectiveness are defined and calculated as part of the MIS. The MIS also requires consideration of other transportation modes as well as broader public and agency input.

Measures Of Effectiveness (MOE)

MOE include: average vehicle speed, vehicle stops, delays, vehicle-hours of travel, vehicle-miles of travel, fuel consumption and pollutant emissions. MOE provide insight into the effects on the traffic stream of the applied improvement strategy.

Metropolitan Planning Organization (MPO)

An association of local agencies established for mutual benefit and to help coordinate planning and development activities within a metropolitan region. Establishment of the MPO is required by law in urban areas of over 50,000 population if federal funds are to be used. The MPO consists of two groups.

1. The Policy board is comprised of officials representing the counties, cities, and state agency.

2. The technical advisory group consists of professional planners and engineers who are usually employees of the same agencies.

The MPO is not a level of government. However, the MPO has "effective control" over transportation improvements within the area since a project must be a part of the MPO's adopted plan in order to receive federal funding.

N

National Highway System (NHS)

The NHS is one of the three major components of the 1991 Intermodal Surface Transportation Efficiency Act. A major new Federal-aid system was established in the NHS. It includes the Interstate System, other routes identified as having strategic defense characteristics, routes providing access to major ports, airports, public transportation and intermodal transportation facilities and, of particular significance to local governments, and many principal urban and rural arterials which provide regional service.

National Transportation System (NTS)

An intermodal system consisting of all forms of transportation in a unified, interconnected manner to reduce energy consumptions and air pollution while promoting economic development and supporting the Nation's preeminent position in international commerce. The NTS includes the National Highway System, public transportation and access to ports and airports.

Non-attainment areas

These are geographical areas, defined by the Environmental Protection Agency, whose air quality does not meet Federal air quality standards designed to protect public health.

North American Free Trade Agreement (NAFTA)

A formal agreement, or treaty, between Canada, Mexico, and the United States of America to promote means for improved and increased free trade between the three countries. The affect of NAFTA on transportation was to increase the need to upgrade existing, and build new, transportation facilities between and within the countries.

Notice Of Intent (NOI)

A notice that is prepared to inform the public that an Environmental Impact Statement will be prepared for a project.

P

Park and Pool (PP)

Similar to Park and Ride, except motorists leave their individual vehicles and complete their trip in a car pool or HOV other than a mass transit vehicle.

Park and Ride (PR)

PR lots are designed to intercept automobiles at outlying locations along transitway corridors (e.g., bus routes). These facilities have been very successful in Texas.

Peak Hour Factor (PHF)

The PHF is a ratio of the total hourly traffic volume to the maximum 15-minute traffic rate within the hour. PHF represents the flow variation within an hour. Observations consistently show the flow rate found in the peak 15-minute period within an hour is not sustained throughout the entire hour. PHFs for multilane highways range from 0.76 to 0.99.

Peak Hour Traffic (PHT)

Higher traffic volumes occur in the evening and in the morning because of work-related trips. The evening peak is typically the highest since non-work related trips are also made in this period. The percentage of Average Daily Traffic (ADT) which occurs in the evening peak hour commonly ranges between 7% and 12%.

Person Trip

A trip by one or more persons in any mode of transportation. Each person is considered as making one person trip. For example, four persons traveling together in one auto make four person trips.

Program

A list of specific actions to be implemented within an identified time period.

R

Record Of Decision (ROD)

The final approval of an Environmental Impact Statement issued by the Federal Highway Administration.

Right Of Way (ROW)

The land (usually a strip) acquired for or devoted to transportation purposes. For example, highway ROW and railroad ROW.

S

Single-Occupant Vehicle (SOV)

A vehicle having only one occupant (usually the vehicle operator!).

Social, Economic and Environmental (SEE)

The SEE affects of a project are assessed in environmental documents such as a Draft Environmental Impact Statement or Environmental Assessment.

Software for Traffic Simulation and Analysis

TRAF is a family of computer software traffic simulation models. It is an integrated software system which consists of five major component models and a variety of supporting programs. TRAF can be used to predict the effect of traffic engineering and Transportation System Management (TSM) strategies on a transportation system's operational performance. TRAF consists of an integrated set of simulation models which, in aggregate, represent the traffic environment. TRAF allows the user to "tailor" the selection of simulation models to specific needs and partition the analysis network into subnetworks, each of which is analyzed at a different level of detail. The TRAF software interfaces the various subnetworks. Components of TRAF are designed to represent traffic in different environments: urban streets (network or arterial), rural roads, and freeways at specific levels of detail (i.e., microscopic or macroscopic). Microscopic simulation models may be used to represent movements of individual vehicles, including influences of driver behavior. Macroscopic simulation models may be used to study changes in circulation patterns and gauge impacts or detailed strategies outside the area in which they are implemented. The simulation models of TRAF are: ROADSIM (microscopic simulation of 2 lane, 2 way rural roads), NETSIM, FREFLO (macroscopic freeway simulation), NETFLO1 and 2 (macroscopic simulations of urban traffic), and FRESIM.

Software name prefixes are:

Software name suffixes are:

CORFLO is for the macroscopic simulation of a corridor and is made of FREFLO and NETFLO1 and NETFLO2. CORFLO is used for analyzing urban transportation networks. The model runs in less time and provides less detailed output than NETSIM.

CORSIM is for simulation and traffic and traffic control conditions of a combined urban and freeway network over a period of time on a microscopic level. CORSIM predicts the effect of traffic engineering and TSM strategies on a prescribed system's operational performance, as expressed in terms of Measures of Effectiveness (MOE). The MOE provide insight into the effects of an applied strategy on the traffic streams, and they also provide the basis for optimizing that strategy.

FRESIM provides a microscopic freeway simulation model for analyzing operational improvements in freeway networks.

FREQ is used for macroscopic modeling of only freeways. It yields results similar to CORSIM.

HCS is Highway Capacity Software designed to replicate procedures, manual worksheets, and examples in the Highway Capacity Manual (HCM) which is issued by the Transportation Research Board. The HCM covers topics including: freeways, freeway weaves and ramps; multilane and two-lane highways; and, urban roadways including signalized and unsignalized intersections, arterials, transit, pedestrians, and bicycles. Changes made in the HCM are also made in the HCS.

NETSIM is used for microscopic simulation and analysis of urban traffic and arterial corridors. Simulation abilities include: different vehicle types (e.g.,buses, trucks, carpool), pedestrian interaction, traffic signs (e.g., yield signs and right turn on red), different signal types (e.g., actuated or fixed time), on-street parking, HOV, and graphic animation. NETSIM simulation results include: delay per vehicle, average speed, number of stops, queue lengths, vehicle origin-destination information, bus routes, and animation.

TSIS. Traffic Software Integrated System. A computer software utility program that provides for use of traffic engineering design and analysis tools. TSIS assists in the installation of traffic engineering applications software and provides menu-driven access to traffic engineering applications software. TSIS provides access to NETSIM, CORFLO, and FRESIM.

Speed

Design speed is the maximum safe speed that can be maintained over a specified section of highway when conditions are so favorable that the design features of the highway govern. The design speed of a roadway dictates which geometric design standards are used such as stopping sight distance, radius of curves, and banking (superelevation) of road surfaces.

Operating speed is the speed at which drivers are observed operating their vehicles.

Posted speed is the maximum speed limit posted on a section of roadway using a regulatory sign. TxDOT's Procedure for Establishing Speed Zones states that the posted speed "should be based primarily upon the 85th percentile speed when adequate speed samples can be secured." This method has also been the standard practice nationwide. Speed limits can not be posted in excess of legislatively mandated speed limits. "85th percentile speed" is the speed at or below which 85 percent of drivers are operating their vehicles.

Statewide Transportation Improvement Program (STIP)

A staged, multi-year, statewide, intermodal program of transportation projects which is consistent with the Statewide Transportation Plan (STP) and planning processes and metropolitan plans, TIPs and processes. The STP is to be implemented within each 3-year period after adoption of the program, and it includes a financial plan that demonstrates how the program can be implemented. Requirement for the STP was established by the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991. The STP is developed in cooperation with the Metropolitan Planning Organization (MPO) programs.

Statewide Transportation Plan (STP)

The official statewide, intermodal transportation plan that is developed through the statewide planning process.

Surface Transportation Program (STP)

A new block grant type program established as one of the three major components of the Intermodal Surface Transportation Efficiency Act to supplement the National Highway System (NHS). The STP may be used by states and localities for any roads, including NHS, that are not functionally classified as local or rural minor collectors. These roads are now collectively referred to as Federal-aid roads.

Surface Transportation Program Category 4C for "Urban Mobility/Rehabilitation" (STP4C)

This funding category is to address transportation needs within the urbanized areas with populations of 200,000 or greater. Restrictions for funding include that the projects are to be selected by the Metropolitan Planning Organization (MPO) in consultation with the Department (TxDOT). These funds can be used on any roadway with a functional classification greater than a local road or a minor collector. Each urbanized area receives an annual allocation based upon population. Federal funds are allocated through the District (TxDOT) to the qualifying MPO (Austin Transportation Study).

T

Transportation Analysis

Corridor analysis is a detailed analysis of a roadway performed for the purpose of obtaining the most accurate projected traffic volumes. The analysis takes into account existing traffic volumes, projected growth, and major traffic generating locations. A corridor analysis will yield projected traffic volumes for every movement allowed on a facility including main lane, ramp, frontage road, and turning volumes.

Design analysis is an analysis is used to determine the number of lanes required to deliver a specific LOS based on a forecast demand volume and given geometric design standards.

Operational analysis is an analytic evaluation of operations on an existing highway segment. The same type of analysis may be applied to evaluate probable operating conditions on a future facility. All traffic and roadway conditions must be specified, as well as traffic volumes. The typical situations which can be resolved through this type of analysis include the comparison of flow conditions for different volume levels and number of lanes. This type of analysis might also be used to establish the impacts of a change in the number of access points along a given section of multilane highway. Another typical application of an operational analysis might be to develop several alternative packages which would be used to improve the level of service or travel speed along a multilane highway.

Planning analysis is similar to Design analysis in that the number of lanes needed for a LOS is determined. However, the Planning Analysis requires much less input of detail, and it uses a very rough estimate for directional design hourly volume and using the design procedures.

Texas Department of Transportation (TxDOT)

A State agency responsible for planning, constructing, maintaining, inspecting, regulating, and distributing funding for state transportation facilities including roads, bridges, waterways, and airports (to a degree). TxDOT also provides technical assistance to counties. Formerly known as the State Department of Highways and Public Transportation (SDHPT). Unofficially known as the Highway Department.

Texas Natural Resources Conservation Commission (TNRCC)

A State agency charged with protecting water and air resources of the state. TNRCC also regulates hazardous material sites.

Transportation Demand Management (TDM)

TDM includes actions or programs which encourage people to travel at alternative times, or with fewer vehicles to reduce congestion. TDM reduces traffic volumes through methods including: ridesharing, park-and-ride operations, staggered work hours, and transit improvements.

Transportation Improvement Program (TIP)

The TIP is a staged, three- to five-year prioritized program of transportation projects covering a metropolitan planning area which is consistent with the metropolitan transportation plan. The projects are recommended from those in the transportation systems management element and the long-range element of the planning process. This program is required for a locality to receive federal transit and highway grants. The selected projects need to be consistent with the transportation plan. The TIP also contains an annual or biennial element which lists all transportation project activities that will receive federal funding for a given 1 or 2 year period. Regulations require the Metropolitan Planning Organization (MPO) and state and transit operators to cooperatively develop the TIP and make project selections within expected funding levels.

Transportation Management Area (TMA)

An urbanized area with a population over 200,000 (as determined by the latest decennial census) or other area when TMA designation is requested by the Governor and the Metropolitan Planning Organization (MPO), and officially designated by the Federal Highway Administration and the Federal Transit Administration. The TMA designation applies to the entire metropolitan planning area served by an MPO within which the TMA is located.

Transportation Strategy

A general approach to solving a transportation problem. Examples of transportation strategies for roadways include: "do nothing" or "no-build," add a travel lane, convert a travel lane to an HOV lane, reconstruct or widen a roadway, or implement Transportation Demand Management and Transportation Systems Management

Transportation System Management (TSM)

Actions or construction that control or improve the movement of cars and trucks on the highway system and buses on the transit system. TSM also includes the coordination of the available transportation systems for more efficient operation.

Transportation Systems Management (TSM)

Some TSM concepts represent over 80 years of experience and practice by transportation engineers and planners. A typical TSM activity is a low-cost, short-term, high-impact transportation-related improvement. A TSM action is not the construction of a new freeway, but it may be the use of a freeway shoulder as an added traffic lane during peak traffic flow conditions. TSM examples include using traffic signals at freeway on-ramps to meter traffic, improving existing signal timings, and using changeable message signs (ahead traffic condition information), lane control signs, and changeable speed signs. TSM involves making implementable improvements, or additions, to existing transportation facilities.

U

Unified Transportation Program (UTP)

A ten year planning document that guides and controls project development for TxDOT in a feasible and economical manner. The UTP is updated annually and requires approval by Texas Transportation Commission. Annual updating allows the UTP to be customized as the Intermodal Surface Transportation Efficiency Act (ISTEA) programs become better defined, and the annual updating also enables the UTP to serve as an integral part of the planning process required by ISTEA.

V

Vehicle Mile of Travel (VMT)

A unit to measure vehicle travel made by a private vehicle, such as an automobile, van, pickup truck, or motorcycle. Each mile traveled is counted as one vehicle mile regardless of the number of persons in the vehicle.

Vehicles Per Day (VPD)

This is a measure of traffic volume and is used as the unit for Average Annual Daily Traffic.

Vehicles Per Hour (VPH)

A ratio used in defining the hourly volume.

Volume-to-Capacity ratio (V/C)

The ratio of flow rate to capacity. The V/C may be the actual or projected rate of flow on a designated lane group during a peak 15-minute interval divided by the capacity of the lane group. The V/C ratio is a measure of capacity sufficiency, that is, whether or not the physical geometry provides sufficient capacity for the subject movement. Low V/C ratios depict relatively free flow conditions. High V/C ratios depict more congested conditions. Actual V/C ratios are calculated from vehicle count data (defining volume) and the geometrics of a roadway (determining capacity). V/C ratios are used to broadly define problem areas on a freeway and to make preliminary operational decisions concerning the freeway (e.g., ramp metering rates). In some cases, the V/C ratio is used to define Level of Service.

W

Weaving Area

A section of a highway where two or more vehicle flows must cross each other's path along a length of the freeway. Weaving areas are usually formed when merge areas are closely followed by diverging areas. They are also formed when a freeway on-ramp is followed by an off-ramp and the two are connected by a continuous auxiliary lane.

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