San Bruno grade separation project nears half-way mark
The San Bruno Grade Separation Project, which will dramatically enhance safety at three rail crossings in downtown San Bruno, is nearing the half-way mark. The supports and bridges for the $147 million public safety project are clearly visible, giving the public a clear idea of the size and scope of the grade separation.
The project will raise the train tracks by 18 feet and lower the road by about four feet at three crossings—San Bruno, San Mateo and Angus avenues. The current station at Sylvan Avenue also will be replaced by a new station on the grade separation between San Bruno and San Mateo avenues.
There will be three pedestrian underpasses – one in the vicinity of Sylvan Avenue, one at the new station and another between Euclid Avenue and Walnut Street. Elevators will provide easy access for riders with disabilities. A total of 201 parking spaces and a “kiss and ride” for dropping off and picking up passengers will serve the station at the site of the former San Bruno Lumber.
The project will include extensive landscaping on the east and west sides of the grade separation, as well as a fountain and an expanded and enhanced Posy Park on the west side.
Grade separations reduce accidents by separating vehicle and pedestrian traffic from train tracks at railroad crossings. Since the Ralston/Harbor/Holly Grade Separation Project in Belmont and San Carlos was completed in 2001, there have been only two fatalities in the area. Before the grade separation five fatalities occurred in the area over an eight-year period.
For contractors, the location of the San Bruno project is one of its most challenging aspects: Interstate 380 is at the northern boundary of the project; San Bruno Avenue is a busy east-west arterial connecting to Highway 101; San Mateo Avenue, the main entryway to downtown San Bruno, crosses the intersection; and the BART tracks to San Francisco International Airport run underneath the project area. In addition, Caltrain operates 86 trains every weekday beginning before dawn until midnight through the construction area.
Construction kicked off at the end of 2010 and, until recently, much of the work has been underground. A shoofly, temporary train tracks to be used during construction, was built. Utilities, including sewer, water, power and telecommunications lines, were relocated. Work on a box culvert, which will increase the capacity of San Bruno’s main storm drain, is underway.
Because the site is directly over the BART extension to SFO, the weight of the entire project cannot exceed the weight of the soil before the construction of the grade separation. A total of 65,000 cubic yards of soil will be removed from the site.
The soil is being replaced with lightweight fill that weighs just 35 pounds per square foot compared to the weight of the soil, which is 120 pounds per square foot. The fill, which will be mixed on site, is a combination of sand, cement and a chemical propellant and is being blown into place.
The 30-foot support structures for the project are made of reinforced concrete. They sit on steel piles that were driven into the ground at varying depths, some of which are more than 70 feet deep. The number of piles varies from 30 to 66, depending on their location. At total of 349 piles were used in the support structures.
The steel train bridges over San Bruno, San Mateo and Angus avenues were installed over three weekends in July. The work provided dramatic footage for a youtube video shot by an interested neighbor.
The next step in the project will be to install the steel boarding platforms for the train station. Because the platforms do not support the weight of the train, they are much lighter; only one crane will be needed to put them in place and the work is expected to take less time than the bridge installations. At 800 feet, the station will be one of the longest in the Caltrain system.
The installation of the Mechanically Stabilized Earth or MSE walls will start this month. These prefabricated walls rely on the friction between the fill and the panel to hold the panels in place. Compared to reinforced concrete walls, MSE walls are easier and faster to install. MSE walls also were used in the grade separation project in Belmont and San Carlos.
The box culvert will be completed before the rainy season. The culvert will increase the capacity of the city’s existing storm drain system, which will help reduce the chance of flooding during heavy rains.
Also to be completed by fall, the shoring, piles and steel plates used for the excavation will be removed. The shoring is so close to the train tracks that the removal work must be done at night, when trains are not operating. The piles, which were installed by vibrating them into place, will be removed the same way.
Plans call for the trains to “cutover” to the new, elevated tracks next spring. After that, the shoofly will be removed and construction of the southbound platform will begin.
The entire project is scheduled to be completed by fall 2013. According to Caltrain’s most recent ridership count, more than 400 people use the San Bruno station on an average weekday. Ridership at the station has increased 7 percent since 2009.
The project is funded by $85.6 million in sales tax revenues from Measure A, a voter-approved half-cent sales tax for transit and transportation projects in San Mateo County. Those Measure A dollars were leveraged to attract $54.8 million in state funds and $6.6 million in federal funds. Fifteen percent of all the funds collected under the reauthorized measure (approved by voters in 2004) are allocated to Caltrain grade separation projects.