A hybrid electric bus is a bus that combines a conventional

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...

propulsion Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body (or an articulated rigid body) but may also concern a fluid. The term is derived from ...

system with an

electric Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

propulsion system. These types of buses normally use a diesel–electric powertrain and are also known as hybrid diesel–electric buses. The introduction of

hybrid electric vehicle A hybrid electric vehicle (HEV) is a type of hybrid vehicle that couples a conventional internal combustion engine (ICE) with one or more electric engines into a hybrid vehicle drivetrain, combined propulsion system. The presence of the electri ...

s and other green vehicles for purposes of

public transport Public transport (also known as public transit, mass transit, or simply transit) are forms of transport available to the general public. It typically uses a fixed schedule, route and charges a fixed fare. There is no rigid definition of whic ...

forms a part of

sustainable transport Sustainable transport is transportation sustainability, sustainable in terms of their social and Environmental issue, environmental impacts. Components for evaluating sustainability include the particular vehicles used; the source of energy; and ...

schemes.

Powertrain

Types of hybrid vehicle drivetrain

A hybrid electric bus may have either a parallel powertrain (e.g., Volvo B5LH) or a series powertrain (e.g., some versions of the

Alexander Dennis Enviro400 MMC The Alexander Dennis Enviro400 MMC (sold as the Alexander Dennis Enviro400) is a low-floor bus, low-floor double-decker bus produced by the British bus manufacturer Alexander Dennis since 2014, replacing the Alexander Dennis Enviro400. The Envir ...

). Since 2003,

Allison Transmission Allison Transmission Holdings Inc. is an American manufacturer of commercial duty automatic transmissions and hybrid propulsion systems. Allison products are specified by over 250 vehicle manufacturers and are used in many market sectors, includi ...

has produced dual-mode hybrid drive units which take the place of a conventional transmission, mostly for transit buses in North America; as the name implies, it is able to switch between series and parallel modes.

Plug-in hybrid

A plug-in hybrid school bus effort began in 2003 in Raleigh, NC, when Advanced Energy began working between districts across the country and manufacturers to understand the needs of both. The effort demonstrated both a technical and business feasibility and as a result was able to secure funding in 2005 fro
NASEO
to purchase up to 20 buses. The resulting RFP from Advanced Energy was won by IC Bus using a product jointly produced with Enova for a 22-mile plug-in hybrid product with a $140k premium over existing buses. The buses performed well in testing with 70% reductions in fuel usage although only in specific conditions. The

United States Department of Energy The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and energy production, the research and development of nuclear power, the military's nuclear w ...

(USDOE) announced the selection of Navistar Corporation for a cost-shared award of up to $10 million to develop, test, and deploy plug-in hybrid electric (PHEV) school buses. The project aims to deploy 60 vehicles for a three-year period in school bus fleets across the nation. The vehicles will be capable of running in either electric-only or hybrid modes and will be recharged from a standard electrical outlet. Because electricity will be their primary fuel, they will consume less petroleum than standard vehicles. To develop the PHEV school bus, Navistar will examine a range of hybrid architectures and evaluate advanced energy storage devices, with the goal of developing a vehicle with a electric range. Travel beyond the range will be facilitated by a clean Diesel engine capable of running on renewable fuels. The DOE funding will cover up to half of the project's cost and will be provided over three years, subject to annual appropriations.

Tribrid Bus

* Tribrid buses have been developed by the

University of Glamorgan The University of Glamorgan () was a public university based in South Wales, that merged with University of Wales, Newport to form the University of South Wales in April 2013. The university was based in Pontypridd, in Rhondda Cynon Taf, with ...

in Wales. They are powered by hydrogen fuel or

solar cell A solar cell, also known as a photovoltaic cell (PV cell), is an electronic device that converts the energy of light directly into electricity by means of the photovoltaic effect.

s, batteries and ultracapacitors.

Air pollution and greenhouse gas emissions

A report prepared by

Purdue University Purdue University is a Public university#United States, public Land-grant university, land-grant research university in West Lafayette, Indiana, United States, and the flagship campus of the Purdue University system. The university was founded ...

suggests introducing more hybrid Diesel–electric buses and a fuel containing 20%

biodiesel Biodiesel is a renewable biofuel, a form of diesel fuel, derived from biological sources like vegetable oils, animal fats, or recycled greases, and consisting of long-chain fatty acid esters. It is typically made from fats. The roots of bi ...

(BD20) would further reduce greenhouse emissions and petroleum consumption.

Manufacturers

Current manufacturers of Diesel–electric hybrid buses include Alexander Dennis, Azure Dynamics Corporation
EbusEletra
(Brazil), New Flyer Industries, Tata (India),

Gillig Gillig (formerly Gillig Brothers) is an American designer and Bus manufacturing, manufacturer of buses. The company headquarters, along with its manufacturing operations, is located in Livermore, California (in the East Bay (San Francisco Bay A ...

, Motor Coach Industries,

Novabus Nova Bus is a Canadians, Canadian transit bus manufacturer headquartered in Saint-Eustache, Quebec. Nova is owned by the Volvo Group. The company has roots in the General Motors Diesel Division, which opened in 1979. Nova Bus was established i ...

, Orion Bus Industries,

Daimler AG Mercedes-Benz Group AG (formerly Daimler-Benz, DaimlerChrysler, and Daimler) is a German multinational automotive company headquartered in Stuttgart, Baden-Württemberg, Germany. It is one of the world's leading car manufacturers. Daimler-B ...

's Mitsubishi Fuso,

MAN A man is an adult male human. Before adulthood, a male child or adolescent is referred to as a boy. Like most other male mammals, a man's genome usually inherits an X chromosome from the mother and a Y chromosome from the f ...

, Designline,

BAE Systems BAE Systems plc is a British Multinational corporation, multinational Aerospace industry, aerospace, military technology, military and information security company, based in London. It is the largest manufacturer in Britain as of 2017. It is ...

Volvo Buses The Volvo Group (; legally Aktiebolaget Volvo, shortened to AB Volvo, stylized as VOLVO) is a Swedish multinational manufacturing corporation headquartered in Gothenburg. While its core activity is the production, distribution and sale of truck ...

, VDL Bus & Coach, Wrightbus
Castrosua
Tata Hispano and many more. Toyota claims to have started with the Coaster Hybrid Bus in 1997 on the Japanese market. Since 1999, Hybrid electric buses with gas turbine generators have been developed by several manufacturers in the US and

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

, with the most successful design being the buses made by Designline of New Zealand. The first model went into commercial service in

Christchurch Christchurch (; ) is the largest city in the South Island and the List of cities in New Zealand, second-largest city by urban area population in New Zealand. Christchurch has an urban population of , and a metropolitan population of over hal ...

since 1999, and later models were sold for daily service in

Auckland Auckland ( ; ) is a large metropolitan city in the North Island of New Zealand. It has an urban population of about It is located in the greater Auckland Region, the area governed by Auckland Council, which includes outlying rural areas and ...

Hong Kong Hong Kong)., Legally Hong Kong, China in international treaties and organizations. is a special administrative region of China. With 7.5 million residents in a territory, Hong Kong is the fourth most densely populated region in the wor ...

Newcastle upon Tyne Newcastle upon Tyne, or simply Newcastle ( , Received Pronunciation, RP: ), is a City status in the United Kingdom, cathedral city and metropolitan borough in Tyne and Wear, England. It is England's northernmost metropolitan borough, located o ...

, and

Tokyo Tokyo, officially the Tokyo Metropolis, is the capital of Japan, capital and List of cities in Japan, most populous city in Japan. With a population of over 14 million in the city proper in 2023, it is List of largest cities, one of the most ...

. The Whispering Wheel bus is another HEV using in-wheel motors. It was tested in winter 2003–04 in

Apeldoorn Apeldoorn (; Dutch Low Saxon: ) is a municipality and city in the province of Gelderland in the centre of the Netherlands. The municipality of Apeldoorn, including the villages of Beekbergen, Loenen (Apeldoorn), Loenen, Ugchelen and Hoenderloo ...

in the Netherlands. In Japan, Mitsubishi Fuso have developed a diesel engine hybrid bus using lithium batteries in 2002, and this model has since seen limited service in several Japanese cities. The Blue Ribbon City Hybrid bus was presented by Hino, a Toyota affiliate, in January 2005. For the North American transit bus market, New Flyer Industries,

, and Nova Bus produce hybrid electric buses using components from either

(series hybrid, initially branded HybriDrive and now branded Series-E), or

(parallel/series hybrid, branded Hybrid EP or H 40/50 EP). In May 2003 General Motors started to tour with hybrid electric buses developed together with Allison.

General Electric General Electric Company (GE) was an American Multinational corporation, multinational Conglomerate (company), conglomerate founded in 1892, incorporated in the New York (state), state of New York and headquartered in Boston. Over the year ...

introduced its hybrid electric gear shifters on the market in 2005. Several hundreds of those buses have entered into daily operation in the U.S. In 2006, Nova Bus, which had previously marketed the RTS hybrid before that model was discontinued, added a Diesel–electric hybrid option for its LFS series. In the United Kingdom, Wrightbus has introduced a development of the London " Double-Decker", a new interpretation of the traditional red buses that are a feature of the extreme traffic density in London. The Wright Pulsar Gemini HEV bus uses a small Diesel engine with electric storage through a lithium ion battery pack. The use of a 1.9-litre Diesel instead of the typical 7.0-litre engine in a traditional bus demonstrates the possible advantages of serial hybrids in extremely traffic-dense environments. Based on a London test cycle, a reduction in CO₂ emissions of 31% and fuel savings in the range of 40% have been demonstrated, compared with a "Euro-4" compliant bus.

Former hybrid bus manufacturers

* ISE Corporation ThunderVolt (filed for bankruptcy in 2010) * Azure Dynamics (filed for bankruptcy in 2012)

Conversions

Hybrid Electric Vehicle Technologies (HEVT) makes conversions of new and used vehicles ( aftermarket and retrofit conversions), from combustion buses and conventional hybrid electric buses into plug-in buses.

List of transit authorities using hybrid electric buses

Transit authorities that use hybrid electric buses:

North America

United States

Pioneer Valley Transit Authority University of Massachusetts Transit New Flyer Xcelsior articulated bus

Federal funding generally comes from the federal Diesel Emissions Reduction Act. CyRide 419

* ABQ RIDE (

Albuquerque, New Mexico Albuquerque ( ; ), also known as ABQ, Burque, the Duke City, and in the past 'the Q', is the List of municipalities in New Mexico, most populous city in the U.S. state of New Mexico, and the county seat of Bernalillo County, New Mexico, Bernal ...

) * Ann Arbor Area Transportation Authority (AAATA) (

Ann Arbor, Michigan Ann Arbor is a city in Washtenaw County, Michigan, United States, and its county seat. The 2020 United States census, 2020 census recorded its population to be 123,851, making it the List of municipalities in Michigan, fifth-most populous cit ...

) * Autoridad Metropolitana de Autobuses (

San Juan, Puerto Rico San Juan ( , ; Spanish for "Saint John the Baptist, John") is the capital city and most populous Municipalities of Puerto Rico, municipality in the Commonwealth (U.S. insular area), Commonwealth of Puerto Rico, an unincorporated territory of the ...

) * Baltimore, Maryland *

Bee-Line Bus System The Westchester County Bee-Line System, branded on the buses in lowercase as ''the bee-line system'', is a bus system serving Westchester County, New York. The system is owned by the county's Department of Public Works and Transportation. Histor ...

(

Westchester County, New York Westchester County is a County (United States), county located in the southeastern portion of the U.S. state of New York (state), New York, bordering the Long Island Sound and the Byram River to its east and the Hudson River on its west. The c ...

) * Berks Area Reading Transportation Authority (

Berks County, Pennsylvania Berks County (Pennsylvania Dutch language, Pennsylvania Dutch: ''Barricks Kaundi'') is a County (United States), county in the Commonwealth (U.S. state), Commonwealth of Pennsylvania. As of the 2020 United States census, 2020 census, the coun ...

) * Bloomington Transit (

Bloomington, Indiana Bloomington is a city in Monroe County, Indiana, United States, and its county seat. The population was 79,168 at the 2020 United States census, 2020 census. It is the List of municipalities in Indiana, seventh-most populous city in Indiana and ...

) * Broome County Transit (

Broome County, New York Broome County is a county in the U.S. state of New York. As of the 2020 United States census, the county had a population of 198,683. Its county seat is Binghamton. The county was named for John Broome, the state's lieutenant governor whe ...

) * Broward County Transit ( Broward County, Florida) * Capital Area Transportation Authority (

Lansing, Michigan Lansing () is the List of capitals in the United States, capital city of the U.S. state of Michigan. The most populous city in Ingham County, Michigan, Ingham County, parts of the city extend into Eaton County, Michigan, Eaton County and nort ...

) * Capital District Transportation Authority (

Albany, New York Albany ( ) is the List of capitals in the United States, capital city of the U.S. state of New York (state), New York. It is located on the west bank of the Hudson River, about south of its confluence with the Mohawk River. Albany is the oldes ...

) *

Central New York Regional Transportation Authority The Central New York Regional Transportation Authority, commonly referred to as Centro, is a New York State public benefit corporation and the operator of public transport, mass transit in Onondaga County, New York, Onondaga, Oswego County, New ...

(

Syracuse, New York Syracuse ( ) is a City (New York), city in and the county seat of Onondaga County, New York, United States. With a population of 148,620 and a Syracuse metropolitan area, metropolitan area of 662,057, it is the fifth-most populated city and 13 ...

) * Charlotte Area Transit System (

Charlotte, North Carolina Charlotte ( ) is the List of municipalities in North Carolina, most populous city in the U.S. state of North Carolina and the county seat of Mecklenburg County, North Carolina, Mecklenburg County. The population was 874,579 at the 2020 United ...

) * Chatham Area Transit (

Savannah, Georgia Savannah ( ) is the oldest city in the U.S. state of Georgia (U.S. state), Georgia and the county seat of Chatham County, Georgia, Chatham County. Established in 1733 on the Savannah River, the city of Savannah became the Kingdom of Great Brita ...

) *

Chicago Transit Authority The Chicago Transit Authority (CTA) is the operator of public transport, mass transit in Chicago, Illinois, United States, and some of its suburbs, including the trains of the Chicago "L" and List of Chicago Transit Authority bus routes, CTA bu ...

* Citibus (Lubbock, Texas) * Central Ohio Transit Authority (

Columbus, Ohio Columbus (, ) is the List of capitals in the United States, capital and List of cities in Ohio, most populous city of the U.S. state of Ohio. With a 2020 United States census, 2020 census population of 905,748, it is the List of United States ...

) * Clarksville Transit System (CTS) ( Clarksville, Tennessee) * Community Transit ( Snohomish County, Washington) * C-Tran (

Vancouver, Washington Vancouver ( ) is a city on the north bank of the Columbia River in the U.S. state of Washington (state), Washington, located in Clark County, Washington, Clark County. Founded in 1825 and incorporated in 1857, Vancouver had a population of 190, ...

) * CyRide (

Ames, Iowa Ames () is a city in Story County, Iowa, United States, located approximately north of Des Moines, Iowa, Des Moines in central Iowa. It is the home of Iowa State University (ISU). According to the 2020 United States census, 2020 census, Ames ha ...

) * Citilink (

Fort Wayne, Indiana Fort Wayne is a city in Allen County, Indiana, United States, and its county seat. Located in northeastern Indiana, the city is west of the Ohio border and south of the Michigan border. The city's population was 263,886 at the 2020 census ...

) * Cache Valley Transit District (

Logan, Utah Logan is a city in Cache County, Utah, United States. The 2020 United States Census, 2020 census recorded the population at 52,778. Logan is the county seat of Cache County and the principal city of the Logan metropolitan area, which includes Ca ...

) * DART First State (

Delaware Delaware ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic and South Atlantic states, South Atlantic regions of the United States. It borders Maryland to its south and west, Pennsylvania to its north, New Jersey ...

) * Des Moines Area Regional Transit (

Des Moines, Iowa Des Moines is the List of capitals in the United States, capital and List of cities in Iowa, most populous city in the U.S. state of Iowa. It is the county seat of Polk County, Iowa, Polk County with parts extending into Warren County, Iowa, Wa ...

) * Durham Area Transit Authority (

Durham, North Carolina Durham ( ) is a city in the U.S. state of North Carolina and the county seat of Durham County, North Carolina, Durham County. Small portions of the city limits extend into Orange County, North Carolina, Orange County and Wake County, North Carol ...

) * Eureka Transit Service (

Eureka, California Eureka ( ; Wiyot: ; Hupa: ; ) is a city and the county seat of Humboldt County, located on the North Coast of California. The city is located on U.S. Route 101 on the shores of Humboldt Bay, north of San Francisco and south of the Oreg ...

) * GoRaleigh (formerly Capital Area Transit) (

Raleigh, North Carolina Raleigh ( ) is the List of capitals in the United States, capital city of the U.S. state of North Carolina. It is the List of municipalities in North Carolina, second-most populous city in the state (after Charlotte, North Carolina, Charlotte) ...

) * Greater Lafayette Public Transportation Corporation ( Lafayette, IN and

West Lafayette, IN West Lafayette ( ) is a city in Wabash Township, Tippecanoe County, Indiana, Wabash and Tippecanoe Township, Tippecanoe County, Indiana, Tippecanoe Townships, Tippecanoe County, Indiana, United States, approximately northwest of the state capit ...

) * Greater Lynchburg Transit Company ( Lynchburg, VA) * Greenville Area Transit (

Greenville, North Carolina Greenville ( ; ) is the county seat of and the most populous city in Pitt County, North Carolina, United States. It is the principal city of the Greenville, NC Metropolitan Statistical Area, and the List of municipalities in North Carolina, 12t ...

) * Hillsborough Area Regional Transit (

Hillsborough County, Florida Hillsborough County is located in the west-central portion of the U.S. state of Florida. In the 2020 census, the population was 1,459,762, making it the fourth-most populous county in Florida and the most populous county outside the Miami metro ...

) * Howard Transit, (

Howard County, Maryland Howard County is a County (United States), county located in the U.S. state of Maryland. As of the 2020 United States census, 2020 census, the population is 334,529. Since there are no incorporated municipalities, there is no incorporated coun ...

) * IndyGo (

Indianapolis, Indiana Indianapolis ( ), colloquially known as Indy, is the List of capitals in the United States, capital and List of municipalities in Indiana, most populous city of the U.S. state of Indiana and the county seat of Marion County, Indiana, Marion ...

) * Jacksonville Transportation Authority * Kanawha Valley Regional Transportation Authority * Kansas City Area Transportation Authority * King County Metro Transit Authority (

Seattle, Washington Seattle ( ) is the List of municipalities in Washington, most populous city in the U.S. state of Washington (state), Washington and in the Pacific Northwest region of North America. With a population of 780,995 in 2024, it is the List of Unit ...

) * Lane Transit District ( Lane County, Oregon) * Long Beach Transit (

Long Beach, California Long Beach is a coastal city in southeastern Los Angeles County, California, United States. It is the list of United States cities by population, 44th-most populous city in the United States, with a population of 451,307 as of 2022. A charter ci ...

) * LACMTA (

Los Angeles, California Los Angeles, often referred to by its initials L.A., is the List of municipalities in California, most populous city in the U.S. state of California, and the commercial, Financial District, Los Angeles, financial, and Culture of Los Angeles, ...

) * LANta ( Lehigh Valley, Pennsylvania) * Madison Metro Transit (

Wisconsin Wisconsin ( ) is a U.S. state, state in the Great Lakes region, Great Lakes region of the Upper Midwest of the United States. It borders Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michig ...

) * Manatee County Area Transit (

Manatee County, Florida Manatee County is a county in the U.S. state of Florida. As of the 2020 United States census, 2020 U.S. Census, the population was 399,710. Manatee County is part of the Bradenton-Sarasota-Venice, Florida Metropolitan Statistical Area, North Por ...

) *

Massachusetts Bay Transportation Authority The Massachusetts Bay Transportation Authority (abbreviated MBTA and known colloquially as "the T") is the public agency responsible for operating most public transportation services in Greater Boston, Massachusetts. The MBTA transit network in ...

(

Boston, MA Boston is the capital and most populous city in the Commonwealth (U.S. state), Commonwealth of Massachusetts in the United States. The city serves as the cultural and Financial centre, financial center of New England, a region of the Northeas ...

) * MATA (

Memphis, Tennessee Memphis is a city in Shelby County, Tennessee, United States, and its county seat. Situated along the Mississippi River, it had a population of 633,104 at the 2020 United States census, 2020 census, making it the List of municipalities in Tenne ...

) * MATBUS – Metro Area Transit ( Fargo, ND – Moorhead, MN) * Metropolitan Transit Authority of Harris County, Texas (

Houston, Texas Houston ( ) is the List of cities in Texas by population, most populous city in the U.S. state of Texas and in the Southern United States. Located in Southeast Texas near Galveston Bay and the Gulf of Mexico, it is the county seat, seat of ...

) * Minneapolis-Saint Paul Metro Transit * MTA Maryland (

Baltimore, Maryland Baltimore is the List of municipalities in Maryland, most populous city in the U.S. state of Maryland. With a population of 585,708 at the 2020 United States census, 2020 census and estimated at 568,271 in 2024, it is the List of United States ...

) * Nashville Metropolitan Transit Authority, doing business as

WeGo Public Transit WeGo Public Transit is a public transportation agency based in Nashville, Tennessee, Nashville, Tennessee. Consisting of city buses and paratransit, the system serves Nashville and Davidson County, Tennessee, Davidson County. In , the system h ...

New Jersey Transit New Jersey Transit Corporation, branded as NJ Transit or NJTransit and often shortened to NJT, is a state-owned public transportation system that serves the U.S. state of New Jersey and portions of the states of New York and Pennsylvania. It ...

* New York City Transit Authority * New Orleans Regional Transit Authority * Niagara Frontier Transportation Authority (

Buffalo, New York Buffalo is a Administrative divisions of New York (state), city in the U.S. state of New York (state), New York and county seat of Erie County, New York, Erie County. It lies in Western New York at the eastern end of Lake Erie, at the head of ...

) * North County Transit District ( North San Diego County, California) * Orange County Transportation Authority (

Orange County, California Orange County (officially the County of Orange; often initialized O.C.) is a county (United States), county located in the Los Angeles metropolitan area in Southern California, United States. As of the 2020 United States census, the population ...

) * Pioneer Valley Transit Authority (

Springfield, Massachusetts Springfield is the most populous city in Hampden County, Massachusetts, United States, and its county seat. Springfield sits on the eastern bank of the Connecticut River near its confluence with three rivers: the western Westfield River, the ea ...

) * Port Authority of Allegheny County (

Pittsburgh, Pennsylvania Pittsburgh ( ) is a city in Allegheny County, Pennsylvania, United States, and its county seat. It is the List of municipalities in Pennsylvania#Municipalities, second-most populous city in Pennsylvania (after Philadelphia) and the List of Un ...

) * Regional Transportation Commission of Southern Nevada/ Citizens Area Transit (

Las Vegas, Nevada Las Vegas, colloquially referred to as Vegas, is the most populous city in the U.S. state of Nevada and the county seat of Clark County. The Las Vegas Valley metropolitan area is the largest within the greater Mojave Desert, and second-l ...

) * Rhode Island Public Transit Authority (

Providence, Rhode Island Providence () is the List of capitals in the United States, capital and List of municipalities in Rhode Island, most populous city of the U.S. state of Rhode Island. The county seat of Providence County, Rhode Island, Providence County, it is o ...

). 1 gas and 1 diesel for testing use only; diesel was converted gas was hybrid from factory. * Roaring Fork Transportation Authority (

Aspen, Colorado Aspen is the List of municipalities in Colorado#Home rule municipality, home rule city that is the county seat and the List of municipalities in Colorado, most populous municipality of Pitkin County, Colorado, United States. The city population ...

) *

San Diego Metropolitan Transit System The San Diego Metropolitan Transit System (MTS) is a public transit service provider for San Diego County, California. The agency operates a transit system that includes the San Diego MTS bus system, San Diego Trolley, and Rapid (San Diego), Rap ...

/ San Diego Transit (

San Diego, California San Diego ( , ) is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. With a population of over 1.4 million, it is the List of United States cities by population, eighth-most populous city in t ...

) * San Francisco MUNI (

San Francisco, California San Francisco, officially the City and County of San Francisco, is a commercial, Financial District, San Francisco, financial, and Culture of San Francisco, cultural center of Northern California. With a population of 827,526 residents as of ...

) * San Joaquin Regional Transit District (

Stockton, California Stockton is a city in and the county seat of San Joaquin County, California, San Joaquin County in the Central Valley (California), Central Valley of the U.S. state of California. It is the most populous city in the county, the List of municipal ...

) * Santa Clara Valley Transportation Authority - VTA (

Santa Clara County, California Santa Clara County, officially the County of Santa Clara, is the sixth-most populous county in the U.S. state of California, with a population of 1,936,259 as of the 2020 United States census, 2020 census. Santa Clara County and neighboring Sa ...

) * Santa Rosa CityBus (

Santa Rosa, California Santa Rosa (Spanish language, Spanish for "Rose of Lima, Saint Rose") is a city in and the county seat of Sonoma County, California, Sonoma County, in the North Bay (San Francisco Bay Area), North Bay region of the San Francisco Bay Area, Bay A ...

) * Sarasota County Area Transit (

Sarasota County, Florida Sarasota County is a county located in Southwest Florida. At the 2020 United States census, 2020 US census, the population was 434,006. Its county seat is Sarasota, Florida, Sarasota and its largest city is North Port, Florida, North Port. Sara ...

) * Sound Transit ( Puget Sound region, Washington) *

SEPTA SEPTA, the Southeastern Pennsylvania Transportation Authority, is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly four million people througho ...

(

Philadelphia Philadelphia ( ), colloquially referred to as Philly, is the List of municipalities in Pennsylvania, most populous city in the U.S. state of Pennsylvania and the List of United States cities by population, sixth-most populous city in the Unit ...

, Pennsylvania) * Southwest Ohio Regional Transit Authority (

Cincinnati, Ohio Cincinnati ( ; colloquially nicknamed Cincy) is a city in Hamilton County, Ohio, United States, and its county seat. Settled in 1788, the city is located on the northern side of the confluence of the Licking River (Kentucky), Licking and Ohio Ri ...

) * Spokane Transit Authority (

Spokane, Washington Spokane ( ) is the most populous city in eastern Washington and the county seat of Spokane County, Washington, United States. It lies along the Spokane River, adjacent to the Selkirk Mountains, and west of the Rocky Mountain foothills, south o ...

) * TCAT ( Ithaca, NY) * TheBus (

Honolulu, Hawaii Honolulu ( ; ) is the List of capitals in the United States, capital and most populous city of the U.S. state of Hawaii, located in the Pacific Ocean. It is the county seat of the Consolidated city-county, consolidated City and County of Honol ...

) * The Rapid The Interurban Transit Partnership

Grand Rapids, Michigan Grand Rapids is the largest city and county seat of Kent County, Michigan, United States. With a population of 198,917 at the 2020 United States census, 2020 census and estimated at 200,117 in 2024, Grand Rapids is the List of municipalities ...

*Has 5 vehicles used in fixed route service. *

TriMet The Tri-County Metropolitan Transportation District of Oregon (TriMet) is a Transit district, transit agency that serves most of the Oregon part of the Portland metropolitan area. Created in 1969 by the Oregon Legislative Assembly, Oregon legi ...

(

Portland, Oregon Portland ( ) is the List of cities in Oregon, most populous city in the U.S. state of Oregon, located in the Pacific Northwest region. Situated close to northwest Oregon at the confluence of the Willamette River, Willamette and Columbia River, ...

): two vehicles *

University of Michigan The University of Michigan (U-M, U of M, or Michigan) is a public university, public research university in Ann Arbor, Michigan, United States. Founded in 1817, it is the oldest institution of higher education in the state. The University of Mi ...

parking and transportation services (

) *

Utah Transit Authority The Utah Transit Authority (UTA) is a special service district responsible for providing public transportation throughout the Wasatch Front of Utah, in the United States, which includes the metropolitan areas of Ogden, Utah, Ogden, Park City, U ...

(

Salt Lake City Salt Lake City, often shortened to Salt Lake or SLC, is the capital and most populous city of the U.S. state of Utah. It is the county seat of Salt Lake County, the most populous county in the state. The city is the core of the Salt Lake Ci ...

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

) *

Washington Metropolitan Area Transit Authority The Washington Metropolitan Area Transit Authority (WMATA ), commonly referred to as Metro, is a tri-jurisdictional public transit agency that operates transit services in the Washington metropolitan area. WMATA provides rapid transit servic ...

Canada

* Transit Windsor (

Windsor, Ontario Windsor ( ) is a city in southwestern Ontario, Canada. It is situated on the south bank of the Detroit River directly across from the U.S city of Detroit, Detroit, Michigan. Geographically located within but administratively independent of Esse ...

) * Edmonton Transit System (

Edmonton, Alberta Edmonton is the capital city of the Provinces and territories of Canada, Canadian province of Alberta. It is situated on the North Saskatchewan River and is the centre of the Edmonton Metropolitan Region, which is surrounded by Central Alberta ...

) *

Hamilton Street Railway The Hamilton Street Railway (HSR) is the public transport agency for Hamilton, Ontario. The name is a legacy of the company's early period, when public transit in Hamilton was primarily served by streetcars. Although streetcars are no longer us ...

(

Hamilton, Ontario Hamilton is a port city in the Canadian Provinces and territories of Canada, province of Ontario. Hamilton has a 2021 Canadian census, population of 569,353 (2021), and its Census Metropolitan Area, census metropolitan area, which encompasses ...

) *

OC Transpo OC Transpo is the primary Transit district, public transport agency for the city of Ottawa, Ontario, Canada, operating bus rapid transit, light rail, conventional transit bus, bus routes, and door-to-door paratransit in the nation's capital regi ...

(

Ottawa Ottawa is the capital city of Canada. It is located in the southern Ontario, southern portion of the province of Ontario, at the confluence of the Ottawa River and the Rideau River. Ottawa borders Gatineau, Gatineau, Quebec, and forms the cor ...

Ontario Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...

) * RTC ( Quebec City, Quebec) * RTL ( Longueuil, Quebec) * Saskatoon Transit,

Saskatchewan Saskatchewan is a Provinces and territories of Canada, province in Western Canada. It is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and to the south by the ...

* STL (

Laval, Quebec Laval is a city in Quebec, Canada. It is in the southwest of the province, north of Montreal. It is the largest suburb of Montreal, the third-largest city in the province after Montreal and Quebec City, and the thirteenth largest city in Can ...

) * STL ( Lévis, Quebec) * STM (

Montreal, Quebec Montreal is the List of towns in Quebec, largest city in the Provinces and territories of Canada, province of Quebec, the List of the largest municipalities in Canada by population, second-largest in Canada, and the List of North American cit ...

) * STO ( Gatineau, Quebec) *

STS STS, or sts, may refer to: Medicine * Secondary traumatic stress, a condition which leads to a diminished ability to empathize * Sequence-tagged site, a gene-reference in genomics * Soft-tissue sarcoma * Staurosporine, an antibiotic * STS (gene ...

( Sherbrooke, Quebec) * St. Catharines Transit Commission (

St. Catharines, Ontario St. Catharines is the most populous city in Canada's Niagara Region, the eighth largest urban area in the province of Ontario. As of 2021, St. Catharines has an area of and 136,803 residents. It lies in Southern Ontario, south of Toronto ac ...

) * Toronto Transit Commission buses 73 out of 2137 regular buses are hybrid as of 2020ref name="TTC-Srv-Sum"> * Coast Mountain Bus Company (

Vancouver Vancouver is a major city in Western Canada, located in the Lower Mainland region of British Columbia. As the List of cities in British Columbia, most populous city in the province, the 2021 Canadian census recorded 662,248 people in the cit ...

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

) *

BC Transit BC Transit is a provincial Crown corporations of Canada, Crown corporation responsible for coordinating the delivery of public transportation within British Columbia, Canada, outside Greater Vancouver. BC Transit is headquartered in Victoria, Bri ...

(

Kelowna Kelowna ( ) is a city on Okanagan Lake in the Okanagan, Okanagan Valley in the British Columbia Interior, southern interior of British Columbia, Canada. It serves as the head office of the Regional District of Central Okanagan. The name Kelowna ...

and Victoria). * GRT ( Waterloo,

) urrently 6 out of 218 buses in service are hybrid* London Transit Commission (

London, Ontario London is a city in southwestern Ontario, Canada, along the Quebec City–Windsor Corridor. The city had a population of 422,324 according to the 2021 Canadian census. London is at the confluence of the Thames River (Ontario), Thames River and N ...

) * Strathcona County Transit (

Strathcona County Strathcona County is a Specialized municipalities of Alberta, specialized municipality in the Edmonton Metropolitan Region within Alberta, Canada between Edmonton and Elk Island National Park. It forms part of Division No. 11, Alberta, Census Di ...

, Alberta) s of 2014, 10 Nova Bus LFS HEV Diesel–electric hybrid buses remain in service* Halifax Transit,

Halifax, Nova Scotia Halifax is the capital and most populous municipality of the Provinces and territories of Canada, Canadian province of Nova Scotia, and the most populous municipality in Atlantic Canada. As of 2024, it is estimated that the population of the H ...

. Currently owns two hybrid-electric buses. * Lethbridge Transit,

Lethbridge, Alberta Lethbridge ( ) is a city in the province of Alberta, Canada. With a population of 106,550 in the 2023 Alberta municipal censuses, 2023 municipal census, Lethbridge became the fourth Alberta city to surpass 100,000 people. The nearby Canadian ...

. 11 out of 42 buses are hybrid. *

Miway MiWay (; stylized MiWay), also known as Mississauga Transit and originally as Mississauga Transit Systems, is the municipal public transport agency serving Mississauga, Ontario, Canada, and is responsible to the city's Transportation and Wor ...

(

Mississauga Mississauga is a Canadian city in the province of Ontario. Situated on the north-western shore of Lake Ontario in the Regional Municipality of Peel, it borders Toronto (Etobicoke) to the east, Brampton to the north, Milton to the northwest, ...

) * Durham Region Transit * Brampton Transit/ ZUM
Niagara Region Transit
* SSM
1 ex TTC Orion VII NG HEV
* Belleville Transit ( Belleville,

) 1 out of 18 buses is hybrid-electric. Three new hybrid buses are on order.

Asia

China

* Beijing Public Transport * Kunming Bus * Shenzhen Bus Group * Shenzhen Eastern Bus * Shenzhen Western Bus * Jinan Bus * Zhengzhou Bus Group

Hong Kong

* Citybus * New World First Bus *

Kowloon Motor Bus The Kowloon Motor Bus Company (1933) Limited (KMB) is a bus company operating Bus services in Hong Kong, franchised services in Hong Kong. It is the largest bus company in Hong Kong by fleet size and number of bus routes, with over 4,000 buses ...

India

* Delhi Multi-Module Transit * Mumbai BEST CNG-Hybrid

Iran

* Vehicle, Fuel and Environment Research Institute (VFERI)

Pakistan

* TransPeshawar * Greenline, Karachi

Thailand

* BMTA

Europe

Belarus

Minsk Minsk (, ; , ) is the capital and largest city of Belarus, located on the Svislach (Berezina), Svislach and the now subterranean Nyamiha, Niamiha rivers. As the capital, Minsk has a special administrative status in Belarus and is the administra ...

Slutsk Slutsk is a town in Minsk Region, in central Belarus. It serves as the administrative center of Slutsk District, and is located on the Sluch (Belarus), Sluch River south of the capital Minsk. As of 2025, it has a population of 59,450. Geography ...

Germany

Dresden Dresden (; ; Upper Saxon German, Upper Saxon: ''Dräsdn''; , ) is the capital city of the States of Germany, German state of Saxony and its second most populous city after Leipzig. It is the List of cities in Germany by population, 12th most p ...

Hagen Hagen () is a city in the States of Germany, state of North Rhine-Westphalia, in western Germany, on the southeastern edge of the Ruhr area, 15 km south of Dortmund, where the rivers Lenne and Volme meet the Ruhr (river), Ruhr. In 2023, the ...

Lübeck Lübeck (; or ; Latin: ), officially the Hanseatic League, Hanseatic City of Lübeck (), is a city in Northern Germany. With around 220,000 inhabitants, it is the second-largest city on the German Baltic Sea, Baltic coast and the second-larg ...

Munich Munich is the capital and most populous city of Bavaria, Germany. As of 30 November 2024, its population was 1,604,384, making it the third-largest city in Germany after Berlin and Hamburg. Munich is the largest city in Germany that is no ...

Nuremberg Nuremberg (, ; ; in the local East Franconian dialect: ''Nämberch'' ) is the Franconia#Towns and cities, largest city in Franconia, the List of cities in Bavaria by population, second-largest city in the States of Germany, German state of Bav ...

Hungary

Budapest Budapest is the Capital city, capital and List of cities and towns of Hungary, most populous city of Hungary. It is the List of cities in the European Union by population within city limits, tenth-largest city in the European Union by popul ...

– The fleet consists of 28 Volvo 7900A Hybrid (articulated). *

Kecskemét Kecskemét ( ) is a city with county rights in central Hungary. It is the List of cities and towns of Hungary, eighth-largest city in the country, and the county seat of Bács-Kiskun County, Bács-Kiskun. Kecskemét lies halfway between the ca ...

– The fleet consists of 20 Mercedes-Benz Citaro G BlueTec®-Hybrid (articulated).

Norway

* Nettbuss,

Hamar Hamar is a List of cities in Norway, town in Hamar Municipality in Innlandet Counties of Norway, county, Norway. Hamar is the administrative centre of Hamar Municipality. It is located in the Districts of Norway, traditional region of Hedmarken. ...

* Ruter,

Oslo Oslo ( or ; ) is the capital and most populous city of Norway. It constitutes both a county and a municipality. The municipality of Oslo had a population of in 2022, while the city's greater urban area had a population of 1,064,235 in 2022 ...

* Nettbuss,

Trondheim Trondheim ( , , ; ), historically Kaupangen, Nidaros, and Trondhjem (), is a city and municipality in Trøndelag county, Norway. As of 2022, it had a population of 212,660. Trondheim is the third most populous municipality in Norway, and is ...

* Nettbuss, Arendal * Nobina,

Tromsø Tromsø is a List of towns and cities in Norway, city in Tromsø Municipality in Troms county, Norway. The city is the administrative centre of the municipality as well as the administrative centre of Troms county. The city is located on the is ...

* Vestviken Kollektivtrafikk,

Vestfold Vestfold () is a county and a current electoral district in Norway. Located on the western shore of the Oslofjord, it borders Buskerud and Telemark counties. The county administration is located in Tønsberg, Norway's oldest city, and the larg ...

. Scania Citywide.

Romania

* STB,

Bucharest Bucharest ( , ; ) is the capital and largest city of Romania. The metropolis stands on the River Dâmbovița (river), Dâmbovița in south-eastern Romania. Its population is officially estimated at 1.76 million residents within a greater Buc ...

– The fleet consists of 130 Mercedes-Benz Citaro Hybrid. * Transurb, Galati - using 20 hybrid buses model Solaris Urbino 12 Hybrid. * Transurban, Satu Mare - using 17 hybrid buses, 15 Solaris Urbino 12 Hybrid and 2 Solaris Urbino 18 Hybrid. * S.P.M.T.,

Târgoviște Târgoviște (, alternatively spelled ''Tîrgoviște'') is a Municipiu, city and county seat in Dâmbovița County, Romania. It is situated north-west of Bucharest, on the right bank of the Ialomița (river), Ialomița River. Târgoviște was ...

- using 28 Mercedes Citaro Hybrid. * Publitrans 2000,

Pitești Pitești () is a city in Romania, located on the river Argeș (river), Argeș. The capital and largest city of Argeș County, it is an important commercial and industrial center, as well as the home of two universities. Pitești is situated in th ...

- using 20 Mercedes Conecto Hybrid.

UK

The Green Bus Fund is a fund which is supporting bus companies and local authorities in the UK to help them buy new electric buses. *

London Buses London Buses is the subsidiary of Transport for London (TfL) that manages most bus services in London, England. It was formed following the Greater London Authority Act 1999 that transferred control of London Regional Transport (LRT) bus s ...

London London is the Capital city, capital and List of urban areas in the United Kingdom, largest city of both England and the United Kingdom, with a population of in . London metropolitan area, Its wider metropolitan area is the largest in Wester ...

. This is the largest fleet in the UK, with around 2,300 vehicles in use. *

National Express West Midlands National Express West Midlands (NXWM) is bus operator in the West Midlands (county), West Midlands of England. It is a subsidiary of Mobico Group (formerly National Express Group) and is the largest bus operator in the region, as well as one of ...

Birmingham Birmingham ( ) is a City status in the United Kingdom, city and metropolitan borough in the metropolitan county of West Midlands (county), West Midlands, within the wider West Midlands (region), West Midlands region, in England. It is the Lis ...

– 18 currently, 21 more planned *

Stagecoach A stagecoach (also: stage coach, stage, road coach, ) is a four-wheeled public transport coach used to carry paying passengers and light packages on journeys long enough to need a change of horses. It is strongly sprung and generally drawn by ...

Manchester Manchester () is a city and the metropolitan borough of Greater Manchester, England. It had an estimated population of in . Greater Manchester is the third-most populous metropolitan area in the United Kingdom, with a population of 2.92&nbs ...

Oxford Oxford () is a City status in the United Kingdom, cathedral city and non-metropolitan district in Oxfordshire, England, of which it is the county town. The city is home to the University of Oxford, the List of oldest universities in continuou ...

Sheffield Sheffield is a city in South Yorkshire, England, situated south of Leeds and east of Manchester. The city is the administrative centre of the City of Sheffield. It is historically part of the West Riding of Yorkshire and some of its so ...

, Newcastle * Oxford Bus Company, Oxfordshire – 52 currently *

FirstGroup FirstGroup plc is a British multi-national transport group, based in Aberdeen, Scotland.Bath, Somerset Bath (Received Pronunciation, RP: , ) is a city in Somerset, England, known for and named after its Roman Baths (Bath), Roman-built baths. At the 2021 census, the population was 94,092. Bath is in the valley of the River Avon, Bristol, River A ...

Bristol Bristol () is a City status in the United Kingdom, cathedral city, unitary authority area and ceremonial county in South West England, the most populous city in the region. Built around the River Avon, Bristol, River Avon, it is bordered by t ...

Manchester Metroshuttle Free bus is a Free public transport, zero-fare bus system that operates in Greater Manchester. The system was first introduced in Manchester city centre in 2002, with three routes linking the city's major thoroughfares and stations with its ma ...

Leeds Leeds is a city in West Yorkshire, England. It is the largest settlement in Yorkshire and the administrative centre of the City of Leeds Metropolitan Borough, which is the second most populous district in the United Kingdom. It is built aro ...

Essex Essex ( ) is a Ceremonial counties of England, ceremonial county in the East of England, and one of the home counties. It is bordered by Cambridgeshire and Suffolk to the north, the North Sea to the east, Kent across the Thames Estuary to the ...

Reading Buses Reading Transport Limited, trading as Reading Buses, is an English Municipal bus company, municipal bus operator owned by Reading Borough Council, serving the towns of Reading, Berkshire, Reading, Bracknell, Newbury, Berkshire, Newbury, Slough, ...

* Lothian Buses * Cumfybus, Merseyside *

Brighton & Hove Brighton and Hove ( ) is a City status in the United Kingdom, city and unitary authority area, ceremonially in East Sussex, England. There are multiple villages alongside the seaside resorts of Brighton and Hove in the district. It is administe ...

* Stagecoach East Scotland,

Aberdeen Aberdeen ( ; ; ) is a port city in North East Scotland, and is the List of towns and cities in Scotland by population, third most populous Cities of Scotland, Scottish city. Historically, Aberdeen was within the historic county of Aberdeensh ...

* Arriva Yorkshire, from April 2013

Spain

Barcelona Barcelona ( ; ; ) is a city on the northeastern coast of Spain. It is the capital and largest city of the autonomous community of Catalonia, as well as the second-most populous municipality of Spain. With a population of 1.6 million within c ...

( MAN Lion's City Hybrid) * Empresa Municipal de Transportes,

Madrid Madrid ( ; ) is the capital and List of largest cities in Spain, most populous municipality of Spain. It has almost 3.5 million inhabitants and a Madrid metropolitan area, metropolitan area population of approximately 7 million. It i ...

* Figueres, within the electric bus Project, IDAE

Sweden

* Jönköpings Länstrafik,

Jönköping Jönköping (, ) is a Urban areas in Sweden, city in southern Sweden with 112,766 inhabitants (2022). Jönköping is situated on the southern shore of Sweden's second largest lake, Vättern, in the province of Småland. The city is the seat o ...

. MAN Lion's City Hybrid. * Göteborgs Spårvägar,

Gothenburg Gothenburg ( ; ) is the List of urban areas in Sweden by population, second-largest city in Sweden, after the capital Stockholm, and the fifth-largest in the Nordic countries. Situated by the Kattegat on the west coast of Sweden, it is the gub ...

. Volvo 7700 Hybrid. * Storstockholms Lokaltrafik,

Stockholm Stockholm (; ) is the Capital city, capital and List of urban areas in Sweden by population, most populous city of Sweden, as well as the List of urban areas in the Nordic countries, largest urban area in the Nordic countries. Approximately ...

. MAN Lion's City Hybrid.

Other European countries

* Ljubljanski potniški promet (5 Kutsenits Hydra City II/III Hybrid's),

Ljubljana {{Infobox settlement , name = Ljubljana , official_name = , settlement_type = Capital city , image_skyline = {{multiple image , border = infobox , perrow = 1/2/2/1 , total_widt ...

Slovenia Slovenia, officially the Republic of Slovenia, is a country in Central Europe. It borders Italy to the west, Austria to the north, Hungary to the northeast, Croatia to the south and southeast, and a short (46.6 km) coastline within the Adriati ...

* Paris: RATP is using a hybrid electric bus outfitted with ultracapacitors; the model used is the MAN Lion's City Hybrid. * Milan, Italy * Team Trafikk, Trondheim, Norway, with 10 Volvo B5L *

Vienna, Austria Vienna ( ; ; ) is the capital city, capital, List of largest cities in Austria, most populous city, and one of Federal states of Austria, nine federal states of Austria. It is Austria's primate city, with just over two million inhabitants. ...

* PostAuto,

Switzerland Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...

: one vehicle is being tested since April 2010; the test will continue for three years. *

Warsaw, Poland Warsaw, officially the Capital City of Warsaw, is the capital and largest city of Poland. The metropolis stands on the River Vistula in east-central Poland. Its population is officially estimated at 1.86 million residents within a grea ...

, 4 Solaris hybrid (combustion-electric) buses * Luxemburg (Sales-Lentz, Emile Weber and AVL) * Belgium / Flanders (De Lijn) * Belgium / Wallonia (TEC): 90 Volvo 7900H (plug-in hybrid) + 208 solaris (combustion-electric) ordered in 2016Q4

Other countries

Egypt IMUT: http://www.i-mut.net/en/about-us. Curitiba BRT 02 2013 Hybrid bus 6094

* Buenos Aires, Argentina * Public transport in Christchurch, Christchurch,

* Rede Integrada de Transporte, Curitiba, Brazil * Mexico City, Mexico (Metrobus (Mexico City), Metrobús Line 4) * Bogotá, Colombia * Montevideo, Uruguay

References

External links

The Plug-in Hybrid Electric School Bus Project
{{Buses Hybrid electric buses, Plug-in hybrid vehicles