The District’s council chairman wants to spend $40 million from a potential future tax on Internet sales to help fund some major projects in Metro’s multibillion-dollar strategic plan.

(John McDonnell/The Washington Post)

Although the tax is not yet authorized under federal law, Chairman Phil Mendelson (D) pledged to use the revenue from the tax – potentially $30 million to $40 million annually – to help pay for the District’s share of Metro’s proposed long-term projects to upgrade its rail and bus system.

In January, Metro came up with a long-term plan, called Momentum, which includes a variety of large-scale projects — among them building a second tunnel under the Potomac River and increasing the number of eight-car trains on the rail system.

But pulling off those big proposals carries a hefty price tag.

Metro officials have said they will need billions of dollars to execute the long-range plan and have been lobbying local leaders and trade groups throughout the region for backing. Alexandria and Arlington County have expressed support for Metro’s mega projects.

The District’s pledge comes after lawmakers in Maryland and Virginia recently approved taxes to help pay for transportation projects.

Metro has meet with officials at Maryland’s transportation department and leaders in Montgomery and Prince George’s counties to seek support for their plan. The agency has also asked the Northern Virginia Transportation Authority for $12 million in fiscal 2014 to help pay for adding new buses and upgrading power substations so it can run more eight-car trains.