Construction of the 12.3-mile Glendora-to-Montclair extension of the Gold Line will be expensive, costing about $1.5 billion in public funds, while also causing dust, detours and delays in six foothill cities for the next nine years.

But construction alone — likely to be a vivid intrusion into everyday life in these quiet suburbs — will come gift-wrapped in cash. The work will create $2.6 billion in economic output and generate 17,000 jobs, mostly in the hard-hit construction industry, according to a report from Los Angeles-based Beacon Economics, an economic forecasting firm.

“It is just one of the validaters of this project, when you look at the economic benefit these communities will receive,” said Habib Balian, CEO of the Gold Line Construction Authority. “Originally, we think of how it will move people and get people out of their cars. Then there is this additional benefit.”

From the official start of the project on Dec. 2, through early 2027 when passenger service begins, the task of building the train line will require an immense amount of work.

Underground utilities will need to be moved and rebuilt to make room for the new light-rail tracks, overhead electrical wires and power substations. Work will also need to be done on the tracks carrying freight and Metrolink commuter trains along the Gold Line’s path.

Six cities — Glendora, San Dimas, La Verne, Pomona, Claremont and Montclair — will get train stations and parking garages, plus 25 new railway bridges and 26 new street-level crossings, all with multiple gates and signals.

The complex construction project alone will have a direct effect on the area’s economy, as workers eat at local restaurants and buy groceries at local stores, for example.

Directly, about 10,000 construction jobs will be created. Indirectly, the massive train project will bring in related jobs, including 228 workers in architecture, engineering and other businesses, according to the report.

Here are a few other figures included in the report:

• The $1.5 billion in construction costs will generate $480 million in spending by businesses buying equipment and supplies.

• An induced impact, defined as workers spending directly or indirectly related to the project, is estimated at $583 million.

• Specifically, the real estate sector will gain $70 million in revenues from leasing commercial space to businesses near the six stations. Other countywide business sectors expected to grow are hospitals ($29.4 million), commercial and industrial machinery rentals ($21.5 million) and employment services ($20.5 million).

Once operational, the project will add $52 million to the local economy, said Robert Kleinhentz, an author and an economist with Beacon.

The most notable side affect comes from an expected 1,800 additional housing units estimated to sprout up around the light-rail line extension.

“We also have an opportunity to chip away at a very important challenge here in Southern California, our housing deficit,” he said.

Balian said he remembered when his agency was building the original Gold Line from Los Angeles to Pasadena most developers laughed at locating townhomes, condominiums and apartments next to light-rail stations.

They were proved wrong those who took risks, creating a plethora of multi-family housing projects adjacent to Gold Line stations in Chinatown, Highland Park and in Pasadena at Del Mar, Allen and Sierra Madre Villa stations.

“It is a proven success now,” Balian said. “And I think cities are embracing that,”