27 July 2012 ~ 1 Comment

Construction Update: Tunnel contract work starts next week in Union Square area

Construction of a major excavation known as a launch box is underway on 4th Street between Bryant and Harrison streets. At nearly 500 feet long, 50 feet wide and up to 40 feet deep, the launch box will take up most of the block.

In the next three weeks, work to prepare for tunneling will continue to ramp up, with tunneling contractor Barnard Impregilo Healy Joint Venture beginning to construct below-ground walls, called headwalls, and perform ground-stabilization work, called jet grouting, around Union Square. In addition, utility relocation on a half-block section of Columbus Avenue may begin in North Beach.

To facilitate construction in the Union Square area, new traffic modifications are going into effect on Stockton Street, Ellis Street and Grant Avenue.

Here’s what to expect as tunnel preparation continues and Union Square utility relocation proceeds:

  • Tunnel Launch Box (4th Street between Bryant and Harrison streets): The contractor will continue constructing below-ground walls around the perimeter of this major excavation site. Current work hours here are 7 a.m. to 4 a.m., Monday through Friday, and 6 a.m. to 2 p.m. on Saturday. At least two lanes of traffic on 4th Street will remain open at all times.
  • Yerba Buena/Moscone Station Headwalls (4th Street between Folsom and Howard streets):  The tunneling contractor is installing below-ground walls, called headwalls, at the site of the future Yerba Buena/Moscone Station. The walls will cross 4th Street at two points on this block. Current work hours at this site are 7 a.m. to 4 p.m., Monday through Friday. At least two lanes of traffic will remain open at all times.
  • Union Square Utility Relocation (on and around Stockton Street between Market and Post streets): Utility relocation at the site of the future Union Square/Market Street Station is nearing completion. Work is scheduled seven days a week from 7 a.m. to 7 p.m., although night work may be necessary.
  • Union Square Tunneling Preparation (Stockton Street between Ellis and Geary streets and Ellis Street between Stockton and Powell streets): Work begins July 30 on Stockton Street and in early August on Ellis Street. The contractor will begin by performing utility demolition and potholing. Ground stabilization work, called jet grouting, and installation of below-ground walls, called headwalls, will follow. For more information about the traffic modifications going into effect in the Union Square area, check out this recent blog post.

Complete, current three-week construction schedules are available online for Union Square utility relocation work and for the tunnel contract. We also post construction, auto detour and Muni impact information on our project Google Map.

Muni Service Impacts

Current Muni service impacts are described below. As construction begins at additional locations, additional Muni routes may be impacted.

  • The 30 Stockton and 45 Union/Stockton began re-routing in January around major construction sites in Union Square and SoMa. These re-routes will continue throughout the duration of Central Subway construction.
  • The 8X/8AX/8BX Bayshore Express and 91 Owl Muni bus lines began re-routing this month. These re-routes will continue throughout the duration of Central Subway construction.
  • The 38/38L Geary may experience delays around Union Square.

Traffic and Pedestrian Impacts


  • At both active construction sites, at least two lanes on 4th Street will be open to traffic at all times.
  • All I-80 on- and off-ramps will remain open during the day, but brief nighttime ramp closures may be required.
  • Traffic delays are anticipated. Motorists are encouraged to use the onramp at Harrison and 7th streets as an alternative to access westbound I-80 while launch box construction is in progress. Those traveling to the peninsula may prefer to access the I-280 via 6th Street or Highway 101 via 10th Street.
  • Access to Clementina Street between 4th and 5th streets may be restricted at times, but the contractor will facilitate access for deliveries.
  • Sidewalks may be impacted.
  • Electronic messaging boards will be in place and parking control officers and flaggers will monitor and facilitate the flow of traffic as appropriate.

Union Square:

  • Starting July 30, Stockton Street between Ellis and Geary streets will be closed to all traffic except emergency vehicles.
  • Starting July 28, Grant Avenue between Geary and Sutter streets will be converted into a two-way street.
  • Ellis Street between Stockton Street and the Ellis Garage will be closed to westbound traffic. One lane will remain open to eastbound traffic. Vehicles exiting the garage will be able to turn left or right onto Ellis Street.
  • Stockton Street will remain open to cross traffic at O’Farrell and Geary streets, but temporary lane closures near the intersections may be required.
  • Variable message signs and detour signs will be in place, and traffic control officers and flaggers will be on site to direct traffic as appropriate.
  • Sidewalks on Stockton Street between Ellis and Geary streets will remain open, but they may be narrowed to facilitate construction.
  • Temporary closures of the crosswalk that crosses Stockton Street on the south side of Geary Street may be required.

The suggested detour route around construction in SoMa and Union Square is shown on the map below. The map also shows a traffic reroute for local access to Union Square.

We appreciate your continued patience while construction is in progress.

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One Response to “Construction Update: Tunnel contract work starts next week in Union Square area”

  1. Dora 9 March 2017 at 7:13 pm Permalink

    th8uns&#a230;.yokr … thanks….your video is 10x longer than all the other go tutorial videos on YT but yours explains it way better! and the others are boring as.

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