Two years ago, Ms. Roem unseated the area’s 13-term, deeply conservative state assemblyman, becoming the first openly transgender state legislator in the country. Yes, she talks about equality, but it is not the top priority in a way that many people outside her district expect. “At the same time, trans people get stuck in traffic,” she said, looking out at taillights as far as the eye could see. “I am right now literally stuck on Route 28, and I am a transgender woman.”

Traffic has a way of subsuming all other issues here. It distorts daily life and separates families. It’s destroying what people who moved out here believed was the good life awaiting them, and what to do about that is a political question, too.

Suburbia is now the nation’s political battleground, as college-educated white voters have shifted toward the Democratic Party and as more racially and economically diverse residents have moved in. But this is a second kind of suburban politics: not the politics of abortion or gun control or bathroom bills, but the politics of development and traffic and growth.

The two currents are not unrelated. The same population boom in Northern Virginia that has turned more suburbs blue has also worsened the gridlock.

Life out here for many families is premised on a precarious trade-off: The housing is more affordable, the neighborhoods smell like campfires, and many homes have views of the woods now in full fall colors. But in exchange for those prizes, a vast majority of workers must leave the area, often heading toward Washington 30 miles east of here. The closest metro stop connected to the city is 15 miles away.