Opponents of the Purple Line, the light-rail project that would connect Prince George’s and Montgomery counties, often suggest that it be slowed to allow an evaluation of other transportation options.

And now a federal judge ordered that the construction be delayed until ridership numbers are recalculated because of declining ridership on Metro.

This is absurd.

This project has been studied for more than 25 years. Highway congestion here is regularly ranked among the worst nationally. Clearly, alternatives to commuting by car are the only viable solutions to the mobility problem in this region.

Other options — such as alternative routes, improved bus service, bus rapid transit systems and doing nothing — were all rejected after extensive research and public input. Some suggested alternatives — self-driving cars and Uber taxis, which would be stuck on the same roads that are already too crowded — couldn’t pass a laugh test. And a study of bus rapid transit in existing traffic lanes delayed the project for four years.

More than $300 million in local, state and federal funds have been invested in the project to date.

Common sense shows that the Purple Line is the first leg of an inevitable circumferential complement to the Metro system.

Thousands of low-wage workers need an efficient way to travel to job centers in College Park, Silver Spring and Bethesda. Students at the University of Maryland at College Park need ways to get to school without cars because the university continues to reduce parking and raise its price. The Purple Line makes sense, too, if only because we need a faster route between Bethesda and Silver Spring or Takoma Park and College Park.

Commuters need ways to travel between the ends of the Red Line and the northern ends of the Green and Orange lines and three MARC lines. The Purple Line would shorten their trips and provide alternatives for situations such as the ongoing Metro SafeTrack program.

The Capital Crescent Trail would benefit from paving and other improvements. The intent to build rail transit along the Capital Crescent Trail was explicit in Montgomery County’s well-known and farsighted decision to purchase the right of way 28 years ago. Litigious property owners have now been paid to relocate any improvements such as fences and sheds that they built on the publicly owned land.

Hundreds of public hearings were held in the course of the 10-year process of writing the Environmental Impact Statement. Many changes were made to accommodate local concerns. During the year-long cost-reduction exercise, the project’s economic and human importance were strongly affirmed.

Transit-dependent real estate investments are planned all along the route, and some are already underway. That shows deep investor confidence in the project.

The demographics of this region are irrefutable: Growth is going to continue. We are planning for it with projects such as the Purple Line.

Any further delay, contrived by a small number of long-term opponents to the project, would be a denial of enormous public benefit by narrow, selfish interests.

On Aug. 23, the Justice Department filed a request for the federal judge to amend or reconsider his decision based on “fundamental and clear errors of law,” which risk a “manifest injustice” if the project is delayed. Purple Line Now concurs.

Much too much time has already been lost for this essential project.

The writer is president of Purple Line Now.