Seattle Transit Blog often uses condensed acronyms and terms that may be hard to follow for some readers not well-versed in transitspeak.  The glossary below provides definitions for common acronyms/terms you may read in the posts and comments.  Please contact us if you would like a transit/land use relevant term or acronym added to the glossary.



ADA: Americans with Disabilities Act, a national law that requires that transit facilities and vehicles be accessible and usable by people with disabilities.

Ad-hominem: to attack one’s character or motives instead of the subject matter, using emotion and not logic.  This approach of verbal abuse is not tolerated, as stated in our Comments Policy.

APC: Automatic Passenger Counting system, uses pressure mats or infrared sensors at doors of trains and buses to help compile passenger ridership estimates.

APTA: American Public Transportation Association, a national non-profit organization which advocates for public transportation throughout the United States.

APU: Auxiliary Power Unit, allows a trolley bus to detach its polls from the trolley-wires and travel away from the right-of-way designated by the wires.

ARRA: American Recovery and Reinvestment Act, an economic recovery act passed in 2009 which provided stimulus funding and grants to numerous organizations and agencies, including bodies that govern transit operations.

Articulated Vehicle (or “artic”): A bus or train with a hinge the allows it to bend.  60-foot articulated buses are commonly deployed on Metro and Sound Transit’s busiest routes.

ATP: Automatic Train Protection, a system that prevents trains from colliding with each other.

ATU: Amalgamated Transit Union, the largest labor union representing transit workers in North America.  Local 587 represents King County Metro Transit workers.

AVL: Automatic Vehicle Location, helps determine the location of a transit vehicle by either using odometer readings, satellite positioning (GPS), or other methods.

AWV: Alaskan Way Viaduct, a double-decked elevated viaduct that runs along the Seattle waterfront.  Heavily damaged by the Nisqually Earthquake in 2001, the viaduct is slated to be replaced by a controversial deep-bore tunnel.


BAT lane: Business Access and Transit lane, a type of bus lane located on the curbside that permits traffic to use it to access driveways or cross streets but not for through travel.

BMP: Seattle Bicycle Master Plan adopted in 2007.

BNSF: Burlington Northern Sante Fe, operates one of the largest privately-owned railroad networks in the United States.  BNSF owns the mainline tracks through which Amtrak, Sounder, and freight trains run and extracts rents from passenger rail operators.

BRT: Bus Rapid Transit, a mode of bus transit that is non-universally characterized by some or all of the following: higher-capacity vehicles, dedicated lanes, signal priority, off-board fare payment, all-door boarding, or wider stops.

BTC: Bellevue Transit Center (see Transit Center).

BTG: Bridging the Gap, a 9-year levy (2006) to fund improvements and maintenance of transportation infrastructure in the City of Seattle.


C40LF: New Flyer Natural Gas 40′ Low-Floor Bus (see New Flyer).

CAD: Computer-Aided Design or Computer-Aided Dispatch (transit operations).

CBD: Central Business District, typically considered the hub of commercial and financial activity within a city.  Sometimes referred to as “downtown” or “greater downtown.”

CD: Central District, a neighborhood in Seattle that is east of downtown, bordered roughly by 12th Ave, Madison St, 23rd Ave, and I-90.

Central Link: The initial segment of Sound Transit’s regional light rail network, connecting Westlake Station in Downtown Seattle to SeaTac/Airport Station (see Link).

The Counterbalance: refers to a system of hooks and weights used to assist electric streetcars up the portion of Queen Anne Ave N that’s very steep, similar to a cable car. Locals still call that area after that.

CPB/CPT: Cost Per Boarding/Cost Per Trip, the cost incurred from each passenger that rides a transit vehicle.  Calculated by dividing the operating cost of a transit mode over the number of boardings in the same period.

CPS: Convention Place Station, the northernmost station in the DSTT (see Downtown Seattle Transit Tunnel) and the only one not served by Link Light Rail.

CT: Community Transit, the transit agency for Snohomish County, Washington, with the exception of the City of Everett and rural areas that are not taxed and do not receive service.


D-2 Roadway: A two-way exclusive roadway for HOVs and transit running in the median of I-90 from Rainier Ave S to Airport Way S. Connected to the I-90 Express Lanes and the DSTT.

D40LF(R)/D60LF: New Flyer Diesel 40’/60′ Low-Floor (Restyled) Bus (see New Flyer).

DART: Dial-A-Ride-Transit, a transit service operated by King County Metro that can deviate from its fixed route to serve customers by request.

DBT: Deep Bore Tunnel, the current plan to replace the Alaskan Way Viaduct with a deep highway tunnel under downtown.

DDU: Driver Display Unit, the computer console used to control the radio, voice announcements (PA) and fare equipment (ORCA reader and in some cases the fare box).

DE60LF(A): New Flyer Diesel-Electric 60′ Low-Floor Bus (‘A’ indicates BRT-styled design: see New Flyer).

Deadhead: “Deadheading” refers to an out-of-service bus that is: driving from the bus garage to the route terminal, vice versa, or driving between route terminals.  This term is also used in other industries, like rail and air transportation to describe both equipment and crews.

DEIS: Draft Environmental Impact Statement (see Environmental Impact Statement).

DEMU: Diesel Electric Multiple Unit (see Multiple Unit).

DMU: Diesel Multiple Unit (see Multiple Unit).

DOT: Department of Transportation, an agency that is a department or division of a larger municipal government.  Typically responsible for transportation planning and operations within its governed area.

DSTT: Downtown Seattle Transit Tunnel, a 1.3-mile tunnel under Downtown Seattle that was originally built in 1987 to alleviate downtown bus traffic.  Four of the five stations (excluding Convention Place Station) are now served by Link Light Rail.  The tunnel is expected to be exclusive to rail by the opening of North Link, when capacity will be fully dedicated to trains.

DT: Downtown, usually the central business district of a city (see Central Business District).


E-3 Busway: An exclusive roadway for buses that follows the alignment of 5th Ave S. It extends the south end of the Downtown Seattle Transit Tunnel to S Spokane St for access to I-5.

E60LFR: New Flyer Electric 60′ Low-Floor Restyled Trolleybus (see New Flyer).

East Link: The light rail extension from Downtown Seattle to Redmond via Downtown Bellevue.  Scheduled for completion in 2021.

EIS: Environmental Impact Statement, a document required under the State Environmental Policy Act (see SEPA) that assesses potential impacts to the environment and addresses techniques and alternatives to mitigate the impacts.

EMU: Electric Multiple Unit (see Multiple Unit).

ESR/ECR: Eastside (Commuter) Rail, the rail corridor that runs through the heart of the Eastside from Renton to Snohomish (BNSF Woodinville Subdivision). Also a group that advocates commuter rail service in that corridor.

ET: Everett Transit, the transit provider for the City of Everett.

ETB: Electric Trolleybus, a type of electric bus that is powered by connecting trolley poles to two overhead wires.  Seattle is one of six remaining cities in America to use ETBs and has the third largest fleet.  King County Metro is expected to replace its fleet by 2014.

EZRA: A planned BRT line in Puyallup.  Funding is uncertain.


FEIS: Final Environmental Impact Statement (see Environmental Impact Statement).

FHWA: Federal Highway Administration, a division within the United States Department of Transportation that is responsible for the regulation of national highways within the U.S.

FRA: Federal Railroad Administration, a division within the United States Department of Transportation that is responsible for supporting and regulating the U.S. railroad network and corresponding rail transportation activities.

FTA: Federal Transit Administration, a division within the United States Department of Transportation that is responsible for programs that support public transit agencies nationwide.

FTP: Fare Transaction Processor, automatically processes a fare transaction when the payment is made.  More commonly referred to as an ORCA card reader.

FUD: Fear, Uncertainty and Doubt; excessive focus on the uncertainties inherent in any project as a tactic to oppose it.


GHG: Greenhouse Gases, atmospheric gases which emit heat and are often attributed to climate change.  Often used as a metric for reducing carbon and pollutant levels.

GIS: Geographic Information System, a system that stores data in correspondence with geographic location.  Used for spatial analysis and creating maps.

GMA: Growth Management Act, a state law enacted in 1991 to govern population growth, planning, development, and infrastructure.


HCT: High-Capacity Transit, a non-universal term that describes a transit mode that has higher passenger capacity than other transit modes.  Often characterized contextually between modes and within modes.  For example, light rail is considered high-capacity in relation to buses, but not in relation to a grade-separated metro.

Headway: The time between scheduled transit vehicle departures. Routes typically operate on 30, 20, 15 or 10 minute headways.

Heavy Rail: Typically refers to rail using a locomotive or a third-rail, completely grade-separated system.  Usually carries more people for higher capital expense.

HOT: High Occupancy/Toll Lanes, HOV lanes (see High Occupancy Vehicle) which are open to single-occupant vehicles upon paying a toll.

HOV: High Occupancy Vehicle, usually defined as a vehicle with two or more occupants, including transit.

HSR: High-Speed Rail, a term that characterizes passenger rail that operates at a significantly higher speed than normal rail traffic.  Specific speeds vary from region to region, but are typically in excess of 150mph.  In 2009, the Obama Administration announced a program that would set aside ARRA (see American Recovery and Reinvestment Act) funds to upgrade certain U.S. rail corridors to HSR.


ID: International District, a Seattle neighborhood south of Downtown and east of Pioneer Square that contains the Chinatown, Nihonmachi (Japantown), and Little Saigon enclaves.  The neighborhood is served by the IDS Station (see International District Station).

IDS: International District Station, a Link Light Rail and DSTT (see Downtown Seattle Transit Tunnel) station within the International District-Chinatown neighborhood of Seattle, considered to be part of the King Street Station hub.  The station is a major inter-modal transfer point for light rail, commuter rail, and buses.

ITE: Institute of Transportation Engineers, a research, education, and professional organization which connects professionals within the transportation engineering industry.  ITE has published several traffic engineering reference books.

ITS: Intelligent Transportation System, a system that utilizes new technologies in application with transportation systems to increase efficiency and reduce issues that normally arise with conventional transportation systems.


KCDOT: King County Department of Transportation (see DOT).

KCM: King County Metro (see Metro).

Kinkisharyo: Manufacturer of Central Link light rail vehicles; also used to refer to the vehicles themselves.


Lid: a term used to describe a roof that is constructed over a freeway with the purpose of mitigating road noise, reconnecting neighborhoods, and reclaiming space above the freeway of which green space can be built or development rights can be sold off to property developers.  Also referred to as a cap.

LID: Local Improvement District, refers to a collection of property owners within a local district that agree to pay into investments which may yield long-term returns that will outweigh short-term costs.  These investments are typically limited to infrastructure systems, including sidewalks, transit lines, utilities, etc.

Link: short for Link Light Rail, official name for the Puget Sound’s light rail project.  Contains one segment from Seattle to Seatac, another in Tacoma, and more to come.

LOS: Level-of-Service, a concept used to describe the operating condition and performance of a transportation facility. Usually on a letter scale, where A is best and F is worst.

LRT: Light Rail Transit, an urban rail transit mode with rapid-transit style features that is non-universally characterized with any combination of the following: at-grade/mixed-traffic running, lower capacity and slower speeds than heavy rail metros, or electric power.  LRT differs from streetcar/trams by typically utilizing higher capacity trains and sometimes running in grade-separated guideways.

LRV: Light Rail Vehicle, a rail vehicle used in light rail transit systems.  LRVs can run as single-car trains, couplets (two-car trainsets), or multiple-car trainsets (generally up to four).  LRVs are generally built to capably run in streets and have more rapid braking capabilities than heavy rail trains (see Light Rail Transit).


MEHVA: Metro Employees Historical Vehicle Association, a historical organization dedicated to preserving Seattle’s vintage and heritage transit vehicles.  MEHVA often offers public rides on these vehicles.

Metro: King County Metro Transit,  also refers to its predecessor, the Municipality of Metropolitan Seattle, a countywide agency created in 1958 to handle regional wastewater treatment and given authority to operate transit service in 1972.  It was absorbed into King County government in 1994.  Metro can also refer to a high-capacity grade-separated rapid transit system, also often referred to as a ‘subway.’

MLT: Mountlake Terrace, a city within the Seattle Metropolitan Area in Snohomish County.

MPO: Metropolitan Planning Organization (see Puget Sound Regional Council), a body that is typically responsible for governing, planning, and promoting growth policies and plans within a certain area.

MT: Metro Transit (see Metro).

MU: Multiple Unit, a term that describes train vehicles that are capable of running as single units or coupled together as multiple unit trainsets.  Each unit might have a driver’s cab at either end.  Light rail vehicles typically use multiple unit configurations.

MUTCD: Manual on Uniform Traffic Control Devices, the standard governing the use of signs, pavement markings, traffic signals and other such devices found in transportation systems nationwide.

MVET: Motor Vehicle Excise Tax (also known as the car tab tax), an excise tax levied on the purchase of motor vehicles.  MVET funds are a component of the revenue stream for local transit agencies.


New Flyer: a manufacturer of bus vehicles based in Winnipeg, Canada.  Various transit agencies in the Puget Sound region use New Flyer models.  The bus model codes are designated as follows: letter prefix indicates propulsion system. C for compressed natural gas, D for diesel, DE for diesel-electric hybrid, E for electric.  Number indicates vehicle length in feet. Common lengths are 35, 40 (standard) and 60 feet (articulated). Letter suffixes: LF for low-floor, HF or no suffix for high floor.  Additional suffixes may include: R for restyled models and A for BRT style.

NIMBY: Not In My Backyard, a term that characterizes local opposition to a major project that may bring substantial impacts to an area.  NIMBY opposition is prevalent in the planning process of such projects.  Typically, NIMBYs accept the need for a project but seek reasons it should be placed somewhere else.


OBA: One Bus Away, a handy application developed by Brian Ferris that utilizes Metro Transit data and configures it in a user-friendly way to allow riders to obtain real-time arrival information for buses.

OCS: Overhead Contact/Catenary System, a component of an electrification system characterized by suspended wires used to supply electricity to a transit vehicle.

OMF: Operations and Maintenance Facility, often used to describe Central Link light rail’s maintenance base between SODO and Beacon Hill stations.

ORCA: One Regional Card for All, a fare payment system introduced in 2009 to streamline operations and costs associated with the numerous transportation agencies in the Puget Sound area.  The ORCA system uses RFID (see Radio-Frequency Identification) technology and can carry cash value in the way of an E-purse, or regional passes.


PB: Parsons Brinckerhoff, a large planning and engineering consulting firm based in New York.

POS: Port of Seattle, the port district that owns and manages the seaport in Seattle and Sea-Tac Airport.  Its operations are partially funded by the property tax in King County.

PP: PugetPass, a regional pass that allows travel on most area transit agencies. PugetPasses were originally swipe cards before the ORCA (see One Regional Card for All) system was implemented. They are now sold as virtual passes that can be loaded onto an ORCA card.

P&R: Park and Ride, a transit facility with automobile parking that allows transit riders to drive and park, and then take transit.  P&Rs are more common in suburban areas where automobile usage is high and connecting transit is limited.

Prop. 1: Proposition 1, refers to two ballot propositions in 2007 or 2008 which asked voters to approve taxes to implement the ST2 transit plan.  The 2007 initiative, which was defeated, also included a roads expansion plan (see Regional Transportation Improvement District).

PRT: Personal Rapid Transit, a transit mode that is characterized by small pod-like vehicles that run along a fixed guideway under an automated system.  Unlike light rail, capacity is limited to a few individuals, hence the name ‘personal.’  PRT technology has not fully matured and is often controversial in the context of large-scale urban implementation.

PSRC: Puget Sound Regional Council, the MPO (see Municipal Planning Organization) for the Puget Sound region.  PSRC develops and promotes policies that govern regional growth and planning.

PSS: Pioneer Square Station, a transit station serving the DSTT (see Downtown Seattle Transit Tunnel) in the Pioneer Square neighborhood.

PT: Pierce Transit, the transit agency for Pierce County, Washington.  Does not tax or provide service to various outlying areas in the County.


R8A: The WSDOT project that is adding an HOV lane in each direction in the outer roadway on the I-90 bridge.  Meant to replace the center-roadway express lanes when they are used for light rail, the term comes from its designation in an early alternatives analysis.

RCW: Revised Code of Washington, the compilation of all current laws within the State of Washington.

RFA/RFZ: Ride Free Area/Zone in Downtown Seattle which allows passengers to ride without payment within a bounded area.  Local downtown businesses help cover the lost costs associated with free rides.  Those traveling outside of downtown pay upon disembarking.

RFID: Radio-Frequency Identification, a technology system that allows data incorporated into an object (via a chip or tag) to be processed by a reader in a wireless process that uses radio waves.  The ORCA card (see One Regional Card for All) uses such technology.

ROW: Right-of-Way, land that is reserved for a transportation corridor.

RPZ: Restricted Parking Zone, a zone which limits parking to residents or patrons holding a city-issued permit.  Often used to discourage hide-and-rides, where transit riders are using parking spaces typically reserved for other issues.  The City of Seattle implemented RPZ policies around Rainier Valley stations in 2009.

RR: RapidRide, a new type of stream-lined bus service operated by King County Metro expected to open in 2010.  Funded by Transit Now initiative, RapidRide will have a number of BRT-style (see Bus Rapid Transit) features to provide frequent all-day service.  RapidRide lines will be lettered ‘A’ through ‘F’.

RRFP: Regional Reduced Fare Permit, allows senior citizens age 65+ and disabled persons to pay a reduced fare to ride transit (no more than 50% of adult fare).  Good on most transit systems in Western Washington.

RTA: Regional Transit Authority (see Sound Transit).

RTID: Regional Transportation Improvement District, a tri-county agency created by the state to develop a plan to improve the regional road network and submit it to voters for approval. Inactive since its plan was rejected by voters in 2007 (see Proposition 1).


SDOT: Seattle Department of Transportation (see DOT).

SEPA: State Environmental Policy Act, a statute within the State of Washington RCW (see Revised Code of Washington) that creates policies and regulations over activities and projects that may incur environmental impacts.

SLU: South Lake Union, a neighborhood in Seattle south of Lake Union that is currently undergoing urban renewal.  Served by the SLU streetcar, the neighborhood is being planned as a future hub for companies and organizations based in the life sciences.

SLUT/SLUS: South Lake Union Trolley/Streetcar, a 1.3-mile streetcar line that runs from Westlake Center in Downtown Seattle to the South Lake Union neighborhood.  The official name is “South Lake Union Streetcar”, but the other acronym has stuck for obvious reasons.

SMP: Seattle Monorail Project, a now-defunct project that proposed building a single-line monorail from Ballard to West Seattle, which would have been known as the Green Line.

SOV: Single Occupant Vehicle, defined as a vehicle with a single occupant (see High Occupancy Vehicle).

SPMA: Seattle Popular Monorail Authority, a city transit agency (now defunct) charged with implementing the Seattle Monorail Project.

SR: State Route, a road or highway owned by WSDOT.

SRO: Standing-Room Only, a term that typically describes a transit vehicle with no open seats available.

ST: Sound Transit, the short name for the Central Puget Sound Regional Transit Authority, the regional agency that was formed in 1996 and commissioned to plan and implement express bus service, light rail, and commuter rail.  The Sound Transit District spans across King, Snohomish, and Pierce counties.

ST2: Sound Transit 2, the Regional Transit System Plan for Central Puget Sound, the second phase of implementing the regional transit system. The plan was approved by voters in 2008 (see Proposition 1).

ST3: Sound Transit 3, the third expansion of the regional transit system, passed in 2016.

STB: Seattle Transit Blog, a blog about everything transit in Greater Seattle, created by transit wonks for transit wonks.

Swift: The region’s first BRT line, planned and executed by Community Transit between Everett and Aurora Village.


Tacoma Link: The light rail serving Downtown Tacoma, perhaps more accurately described as a streetcar.  There is serious discussion about extending this to serve Tacoma’s neighborhoods.

Talgo: a Spanish manufacturer of railway cars used worldwide including the Amtrak Cascades fleet.

TBD: Transportation Benefit District, a taxing district that funds transportation improvements and projects within that district using voter-approved local revenue sources.

TBM: Tunnel Boring Machine, a large machine with a drill-like component that has the capability of boring large tunnels.  TBMs are often used in construction of rail tunnels.

TC: Transit Center, a facility used as a hub for local transit connections.  Many suburban cities outside of Seattle have transit centers in their downtown areas.

TCC: Transportation Choices Coalition, an advocacy group that often lobbies for pro-transit legislation and ideas in Olympia and around the region.

TDM: Travel (or traffic) demand management, a term used to describe any combination of efforts or strategies aimed at reducing congestion-inducing travel demand.

TDR: Transfer of Development Rights, a growth management program in King County that gives developers rights to build more densely within urbanized areas in exchange for the preservation of rural and environmentally sensitive areas.

Through-routing: Typically refers to the linkage of two transit routes together at a common terminal so that trips passing through the terminal switch routes while continuing to operate revenue service throughout. Through-routing is usually implemented at terminals in dense high-traffic areas where layover space is scarce.

TIB: Tukwila/International Blvd Station, a station on the Link line.  Not to be confused with Tukwila Station, served by Sounder.

TOD: Transit-Oriented Development, any form of real estate development that is located within walking distance of a high-capacity transit station node.  TOD is often characterized by limited parking, pedestrian amenities, and mixed-use development.

Transit Wonk: Any individual that has an unusual yet enthusiastic passion of public transit activities and issues.

Trunk or Trunk route: A transit corridor characterized by frequent service that is medium or high-capacity. Trunks are typically the highest-performing and most productive routes in a transit system.

TSM: Traffic System Management, a term used to describe policies or strategies that actively monitor and manage traffic activities.

TSP: Transit Signal Priority, priority that is given to transit vehicles at an signaled intersection with mixed traffic.

TVM: Ticket Vending Machine, an automated machine that sells tickets or passes.  Sound Transit TVMs also issue ORCA cards.


UGA/UGB: Urban Growth Area, mandated by the GMA (see Growth Management Act), used to preserve rural areas from urban development by limiting the area that can be developed at urban intensities (see maps of Washington State UGAs).  Also called an Urban Growth Boundary (UGB).

University Link: The next segment of light rail to open, adding two stations at Capitol Hill and Husky Stadium.  Scheduled to open in 2016.

UP/UPRR: Union Pacific Railroad, one of the two major railway companies in the State of Washington.

USDOT: United States Department of Transportation, the governing body that regulates transportation activities within the United States (see DOT).

UW: University of Washington, a major research university and the largest in the Pacific Northwest.  Its main campus is in Seattle’s University District with branch campuses in Tacoma and Bothell.


VMT: Vehicle Miles Traveled, a number that measures the number of miles any combination of motorists have traveled.  Often used as a reduction metric among planning agencies.


WS: Westlake Station, a transit station in the DSTT (see Downtown Seattle Transit Tunnel) and the northern terminus of Link Light Rail. The station is considered by the City of Seattle as a transportation hub, with connections to the Seattle Center Monorail and South Lake Union Streetcar above ground.

WSDOT: Washington State Department of Transportation (see DOT ), an agency responsible for the planning and construction of major road projects, as well as ferries in Washington State.

WSF: Washington State Ferries, a division of the Washington State Department of Transportation that oversees the ferry system.  WSF has the largest fleet of ferries in the United States.