Sound Transit is facing a major challenge.

The agency has a $6 billion to $8 billion funding shortfall to build nine rail extensions and two bus-rapid transit routes promised in the voter-approved Sound Transit 3 measure.

Consultants this spring found that the deficit resulted from inaccuracies in early cost estimates along with rapid land and construction price increases.

Traffic Lab is a Seattle Times project that digs into the region’s thorny transportation issues, spotlights promising approaches to easing gridlock, and helps readers find the best ways to get around. It is funded with the help of community sponsors Alaska Airlines, Kemper Development Co., Madrona Venture Group, NHL Seattle, PEMCO Mutual Insurance Company and Seattle Children’s hospital. Seattle Times editors and reporters operate independently of our funders and maintain editorial control over Traffic Lab content.

Federal aid could reduce the funding gap. However, the figures don’t include extra costs for options such as a West Seattle tunnel, a south-end train base over the toxic Midway Landfill or a 200-foot-deep International District/Chinatown station.

To address the shortfall, Sound Transit’s board is considering new construction schedules, known as a “realignment,” that postpone most opening dates two to 10 years in an attempt to manage tax revenue.

A realignment vote could come Aug. 5.

We’d like to hear from you. What questions do you have about possible Sound Transit project delays or additional funding sources? Tell us below or email mbaruchman@seattletimes.com.