INTRO: Construction work is getting under way on the long-planned BART extension to San Francisco International Airport, currently costed at US$1·2bn

BYLINE: Thomas E Margro

General ManagerBay Area Rapid Transit District

AFTER ALMOST a decade of planning, San Francisco’s Bay Area Rapid Transit District has started construction of its long-awaited extension to San Francisco International Airport (SFO), Northern California’s top priority rail project. Excavation work began in November for the 14 km, four-station extension, which will bring rail services to the ’front door’ of the world’s seventh busiest airport, greatly expand BART ridership on the San Francisco Peninsula, and enhance regional rail travel within the entire Bay Area. The $1·2bn project, funded with a mix of federal and state grants and local revenues, is scheduled to enter revenue service in December 2001.

BART is the backbone of regional public transport in the northern California conurbation, which has a population of more than 6 million. Automatically driven metro trains, powered by a 1 kV DC third rail supply, currently operate over 150 route-km, serving 39 stations in the core cities of San Francisco and Oakland, plus 20 outlying communities. Since the first route opened in 1972 more than 1 billion passengers have ridden almost 25 billion passenger-km. In 1997, ridership averaged 270000 passenger journeys per day, with a record total of 76 million trips for the year.

The BART-SFO Extension comprises 12 km of new main line extending south from the existing terminus at Colma to a multi-modal interchange at Millbrae, plus 1·9 km of route running east-west in an elevated ’wye’ to serve the airport. Most of the line will be underground, with sub-surface stations to serve South San Francisco and San Bruno. The Airport station will be elevated, and linked to the departure level of a new International Terminal which is now under construction. The terminus at Millbrae will be built at-grade to enable easy cross-platform transfer to and from the CalTrain commuter rail service between San Francisco and San José in the heart of California’s Silicon Valley.

Ridership on the extension is projected to reach nearly 70000 passenger journeys per day by 2010, including some 20000 trips to the airport.

Economic booster

Bringing rail access to the airport is seen as critically important to the Bay Area’s continued economic vitality. Tourism is a major source of revenue to the region, and the airport is an important gateway for travel to and from the Pacific Rim, Mexico and Latin America. SFO currently handles more than 100000 passengers per day, with annual patronage forecast to climb from 40 million in 1997 to 51 million by 2006. This has prompted the airport authority SFIA to embark on an ambitious expansion plan.

The $2·5bn Airport Master Plan encompasses more than 60 projects, which will significantly increase airline capacity, with a new 26-gate International Terminal. New freeway access ramps and better parking facilities will improve vehicle access, whilst traffic congestion on the airport roads will be reduced by the development of an Airport Rail Transit peoplemover linking the passenger terminals, car rental zone and remote car parks.

More than half of the airport’s perimeter is bounded by San Francisco Bay, the rest by US Highway 101. Opportunities to increase road capacity are constrained by right-of-way and environmental obstacles, making BART virtually the only option for generating a material increase in surface access capacity.

From the north, BART trains will run directly to the airport every 15 to 20 min, with a journey time from central San Francisco of 30 min or less. Leaving the Airport station, at least half of all air travellers will be within a 5 min walk of their airline ticket counter. Air travellers and airport workers will also be able to transfer easily between BART and the ART which will have a stop immediately above the Airport station.

There should be no problem accommodating air travellers on the network, because peak demand at the airport occurs at different times to the normal commuter peaks. BART trains are most heavily used during the morning and evening commuter travel peaks, but most flight arrivals and departures at SFO are bunched around mid-day when BART has plenty of spare capacity.

At BART stations airport-bound passengers with carry-on baggage should be able to pass through the ticket turnstiles without any problem. Those with larger luggage can use the service gates next to the station agents’ booths. Elevators will take them to and from the platform. On the trains, travellers should find space for their bags on an empty seat or on the floor.

In addition to the airport service, the extension will also provide convenient links with other local transport systems; BART already connects with the MUNI light-rail network at several points in San Francisco. Further south San Mateo County Transit District, as a partner in the extension, is also planning to develop frequent bus feeder services to all of the extension stations.

Millbrae Intermodal Station, the extension’s signature station, has been designed around a central platform shared by BART and CalTrain. A free transfer or shared ticket will allow passengers to interchange conveniently between the two systems, which will boast a combined 290 km network with 76 stations covering five Bay Area counties. The station will have five tracks (three BART and two CalTrain) and four platforms accessible by escalator, elevator and stairs from an overhead concourse containing ticketing and fare collection facilities. Also to be built on the 6·4ha station site are a four-level, 2100-space car park, adjacent surface parking for 900 vehicles, and internal bus and car access roads.

As the southern terminus for BART’s Peninsula service, Millbrae is expected to generate the greatest patronage. Ridership is projected to reach 33000 trips per day by 2010, which will make it among the most heavily used stations in the entire network. During the commuter peaks BART trains will run to and from Millbrae every 7 min. A dedicated BART shuttle service from Millbrae to the airport will run every 15 to 20 min, connecting with CalTrain arrivals from the south.

Engineering challenge

The BART-SFO Extension poses numerous design and engineering challenges. In less than 15 km, the alignment traverses five towns, passing by, through, over or under cemeteries, hospitals, schools, a regional shopping centre, a central business district, several residential neighbourhoods, a federally-protected endangered species habitat and an operating railroad. In addition, the location of the Airport station was predetermined by SFIA as part of its airport expansion strategy. The resulting geometry led to the wye configuration, elevated structures and complex trackwork with implications for the train control systems.

The project includes 9·6 km of tunnel, 2·4 km of surface running and 2 km of viaduct. With the San Andreas Fault, the most active earthquake zone in California, less than 2 km away, the seismic criteria incorporated into the design of the extension far exceed anything BART has needed before. Subway and aerial structures are designed to withstand an earthquake rated at up to 8·0 on the Richter scale. Fire safety standards have also been upgraded significantly.

Funding for the SFO extension includes a $750m grant from the Federal Transit Administration, $200m from the airport authority, $108m from the California Transportation Commission, and $99m from the San Mateo County Transit District.

Contracts awarded so far include construction of the main line from Colma to Millbrae for $530m, construction of the Millbrae station for $70·5m, and site preparation and utility relocation works totalling $10m. Combined, these three contracts account for approximately 90% of all BART-contracted construction work on the project. The remaining two construction contracts, for San Bruno and South San Francisco stations, are due to be awarded in the next few months.

The main line contract provides for supply of an operating railway apart from the stations. It includes all civil structures for the main line and the aerial wye west of Highway 101, plus the traction power, communications and train control systems for the entire project. Also included are the airport station and viaducts over and east of the freeway. The contractor, a joint venture of Tutor-Saliba and Slattery, received Notice to Proceed on May 4 1998. Initial works were concentrated at the northern end of the alignment, where a major stormwater drainage culvert had to be relocated out of the path of the line. With that work completed, subway construction began in early November.

The contractor for Millbrae station, a joint venture of Sverdrup Construction Co. and Conco Inc., received its NTP on June 8. The contractor is completing design work and expects to commence major construction shortly. To allow for advance soil testing and to provide access for main line construction, part of the station site has been cleared, requiring the demolition of four buildings. Other works are under way at many locations along the alignment as part of the site preparation contract, for which the NTP was issued in August 1997.

In tandem with this work, construction of the BART airport station and on-airport viaducts is advancing steadily. Concourse H, which will house both the BART station and the ART interchange, is being built under contracts awarded separately by San Francisco International Airport. The foundation of Concourse H, consisting of concrete and steel piles sunk deep into the underlying sediments, and steel-reinforced pile caps and pillars, is nearly complete. Piles, caps and pillars are also being erected for the BART viaducts crossing over Highway 101 and for the combined BART/ART aerial guideways east of the freeway. In addition the link building connecting Concourse H to the new International Terminal is nearly complete.

BART’s South San Francisco station will be situated on 6ha between two major thoroughfares in a light industrial area. Two new streets will provide direct access to bus facilities, a kiss-and-ride interchange, and parking for over 1300 cars. The design provides for an underground central island platform linked to a surface-level concourse containing fare collection and other facilities.

The 4·8ha San Bruno station will be situated immediately adjacent to the Tanforan Park Shopping Centre, a large regional mall. It will also include an off-street bus interchange and a multi-storey car park accommodating 1000 cars. It will also be an island platform underground station with ticket machines on the surface concourse for fare collection, but with other facilities such as machine rooms on an upper level.

CAPTION: Work is already under way for the BART station at San Francisco International Airport. Looking from the top of the link to the International Terminal, the sets of three pillars will carry Concourse H, which will house the station and the interchange with the ART airport peoplemover

CAPTION: A computer-rendered image of San Francisco International Airport after the expansion program shows the elevated wye that will carry BART trains to and from the airport

CAPTION: Alignment and cross-section of the SFO extension, showing the location of the cut-and-cover stations and the elevated section leading into the airport

CAPTION: Preliminary works included relocation of a 300 m storm water drainage culvert at the northern end of the line, completed last October (right), and the demolition of vacant buildings on the site of Millbrae interchange in August (far right) to allow soil testing

CAPTION: Concourse H at SFO will accommodate the BART station and an ART peoplemover stop above. The station will have a three-track layout for operating flexibility, and will offer convenient access to the airport ’s new International Terminal

CAPTION: The main street entrance to Millbrae Intermodal Station will be adjacent to US Highway 101. A shared central platform will allow easy transfers between BART and CalTrain services

La liaison rail-aéroport prend forme

La construction commence sur l’extension du BART en direction l’aéroport international de San Francisco, prévue de longue date. Le projet ferroviaire numéro un de la Californie du nord est une ligne de 14 km et quatre stations, comportant un Y surélevé dans l’aéroport et, à Millbrae, une correspondance quai à quai vers les services banlieue de CalTrain. Financé à la fois par des subventions fédérales et de l’état ainsi que par des imp