The rising cost of construction may fell plans to extend Gold Line service into San Bernardino County.

Yesterday, the Foothill Gold Line Construction Authority announced that the estimated cost of the 12.3-mile, six-station extension has swollen to $2.1 billion - a $570-million increase from two years ago. The revised cost estimate was gleaned from analysis of the bids submitted by four design-build teams competing for the project's Glendora to Montclair Alignment Contract, and exceeds the $1.4 billion in funding that has been identified for the extension.

To make up for this shortfall, the Construction Authority has proposed a pared-down project which would deliver nearly 70 percent of the extension by 2024 - two years ahead of the original schedule. The scope of the revised plan includes eight miles of new track and three stations, with a temporary terminus in the City of La Verne. The Construction Authority would also continue to relocate existing freight rail systems and work on grade crossings along the majority of the project right-of-way.

The proposed plan would include an option to complete the full project to Montclair - including stations in Pomona and Claremont - should funding be secured within two years of the start of construction. In that case, the extension to Montclair would be completed by 2028.

The revised project will be subject to environmental review.

Funds currently identified for the Foothill Extension include $1.1 billion from the countywide sales tax approved under Measure M and $300 million from the State's Transit and Intercity Rail Capital Program. A groundbreaking ceremony for the project was held in December 2017 - just a year after the opening of the Gold Line's most recent extension to Azusa.