The streets of downtown Palo Alto will transform into a hive of construction activity this spring, when the city launches an ambitious, yearslong plan to replace utility pipes, upgrade traffic equipment, widen sidewalks and expand its fiber-optics network.

The construction frenzy is set to launch in April and May and crawl block-by-block along University Avenue and surrounding streets, where roads will be torn up to accommodate new pipes, cables and equipment relating to traffic signals and utilities. Known as "Upgrade Downtown," it will involve the installation of -- among other things -- 17 traffic poles, 84 directional signs, more than 16,000 linear feet of gas pipes, 47 utility boxes, 30 streetlight pull boxes, and 2,470 linear feet of street-light conduit, according to a report from the Utilities Department.

Sidewalks will be widened on the south side of University Avenue and at University's intersections with Tasso and Kipling, creating shorter pedestrian crossings and making room for 12 new bike racks.

And about 2,750 linear feet of fiber cables will be installed within the same trenches as the gas and water pipe lines, with the goal of allowing more residents and businesses to tap into the city's underground fiber-optic network.

Years in planning, the project will be among Palo Alto's most complex, visible and potentially disruptive projects of the year -- also, among the most expensive.

While city engineers had estimated the project to cost about $12.4 million, the Bay Area's sizzling construction climate has inflated the price tag by close to $4 million, according to staff. On Monday, the city is scheduled to approve a $16.3 million contract with the firm Ranger Pipelines, Inc., for the pipe upgrades.

To accommodate the swelling price tag, the city plans to withdraw funds from various reserves in its gas, water and fiber utilities (which are generally thought of as rainy-day funds) and to take about $1 million from programs intended for street maintenance and sidewalk repairs.

The lion's share of the utility work will take place along University, between University Circle and Webster Street, and other Downtown North neighborhood streets. According to staff, that's the area where gas and water mains were identified as most in need of replacement, based on pipe material and age. While the gas mains are the highest priority, utilities staff also identified the replacement of water mains as an upcoming project. To avoid digging twice, staff agreed to combine the two.

Dean Batchelor, chief operating officer at City of Palo Alto Utilities, said both the gas and water lines were near the end of their respective life cycles. He pointed to recent water leaks on University Avenue as a sign that it's time to act.

Then, following the same logic, Utilities Department officials agreed to add fiber to the mix. Citing the City Council's recent advocacy for a "dig once" strategy for installing telecommunication infrastructure and its general support for expanding the city's dark-fiber-optic network, officials plan to install 2,750 linear feet of conduit in the same trenches that will contain the new gas and water pipes.

"One of the thoughts was, since we really don't have any fiber conduit going down University Avenue and since we're going to tear up 26 blocks, it made sense to go ahead and put in 2-inch fiber conduits," Batchelor said.

The installation of fiber cables is expected to improve the reliability of the city's fiber-optic network, which is currently congested because of heavy demand, said David Yuan, strategic business manager at Utilities. It will not, however, provide the type of "fiber-to-the-node" or "fiber-to-the-premise" service that council members have been pursuing, on and off, for nearly two decades.

Under the fiber-to-the-premise model, the municipal dark fiber network would be expanded throughout the city, allowing most residences and businesses to opt in and get ultra-high-speed broadband. The more cautious and incremental "fiber-to-the-node" model would establish nodes at various points in the city and then allow neighborhoods to tap into the network as funding for "last-mile" connections becomes available..

Yuan said that the while the newly installed fiber may enable such services in the future, the city will first have to complete a comprehensive design for a citywide network.

The biggest and most expensive component of the downtown project is the replacement of water and gas distribution pipes with high-density and medium-density polyethylene, respectively. The replacement, according to staff, will "eliminate leaks in the project area through the fusion of joints, increase the reliability and protection of the water and gas distribution systems, increase required flow and pressure for fire protection, make the system more resilient against corrosion and earth movement, and reduce energy costs."

Batchelor said the work along and around University Avenue alone is expected to take about 12 months. One by one, each block of University will be closed off to traffic, though city officials say pedestrians will be able to get to downtown businesses unimpeded.

The city will then move on to other parts of downtown, with the goal of completing all the work by 2021. Once the pipes are in place, work will begin on street improvements, including installation of federal Americans with Disabilities Act-compliant ramps and sidewalk expansions.

According to the Utilities Department's schedule, street-improvement work will begin in 2019 on Hawthorne Avenue (between Emerson Street and Middlefield Road), on Everett Avenue (between Middlefield and Alma Street) and on Emerson Street (between Channing and Forest avenues). In 2020, the city plans to move on to Emerson (between Forest and Palo Alto avenues) and Webster Street (between Lytton and Hawthorne avenues).

More information about Upgrade Downtown is available here.