Transportation is about more than just moving people from point A to point B. It’s also a system that can either limit or expand the opportunities available to people based on where they live. In many cities, the areas with the shoddiest access to public transit are the most impoverished—and the lack of investment leaves many Americans without easy access to jobs, goods, and services.

To be certain, the aging and inadequate transportation infrastructure is an issue for Americans up and down the economic ladder. Throughout the country highways are crumbling, bridges are in need of repair, and railways remain inadequate. Improvement to public transportation—buses, trains, and safer routes for bicycles—is something that just about everyone who lives in a major metropolitan area has on their wish list. But there’s a difference between preference and necessity: “Public transportation is desired by many but is even more important for lower-income people who can't afford cars,” says Rosabeth Moss Kanter, a professor at Harvard University and author of a new book Move: Putting America’s Infrastructure Back in the Lead.

“Without really good public transportation, it's very difficult to deal with inequality,” Kanter said. Access to just about everything associated with upward mobility and economic progress—jobs, quality food, and goods (at reasonable prices), healthcare, and schooling— relies on the ability to get around in an efficient way, and for an affordable price. A recent study from Harvard found that geographic mobility was indeed linked to economic mobility, and a 2014 study from NYU found a link between poor public-transit access and higher rates of unemployment and decreased income in New York City.

Access to good transit is not merely a question of a system’s geographic reach but also the cost to ride—and the latter is becoming an issue more and more. In the past five years many metro areas including New York, Portland, and St. Louis have seen fare hikes that place additional strain on low-income households. Recent additions to public transportation options, like bike share, should—in theory—make getting around easier and cheaper. But as it’s widely been noted, these programs tend to place their kiosks, at least at first, in more affluent neighborhoods. They also require credit cards for rental, which leaves out poorer populations who tend to not have access to such financial instruments. A recent survey of bike share users in Washington D.C., for example, found that ridership wasn’t particularly reflective of the city’s population: The city has a population that is about 50 percent black but the study found that bike-share ridership was made of up of mostly young, white males, and more than 50 percent of those using the region’s bike share system had incomes of $100,000 or more.  

That leaves most low-income households to rely on older transportation methods—and therein lies the problem.

For those living in less central neighborhoods, buses typically provide a crucial link to main subway lines. That, too, can be problematic. Bus fleets are old and breakdowns are common. Kanter says that in her interviews with public-transit users, complaints about bus systems were widespread. “They reported that bus drivers sometimes didn't complete routes late at night because there were very few passengers and the neighborhoods were considered dangerous. Or bus drivers would sometimes pass people by standing at bus stops.” Bus stops were also in disrepair, providing inadequate shelter from precipitation or severe cold—a problem that is exacerbated by the book’s finding that even in cities that allow for digital tracking, bus arrival and departure times are often erroneous, leaving people to wait for untold periods of time. And thanks to overcrowding and inadequate space for things like grocery bags or bikes, once a bus arrives, passengers often can’t manage to get on.

That means America’s inadequate public transit leaves many Americans hoping to better themselves stuck—both metaphorically and quite literally.

There is no silver bullet. Kanter says that creating rapid bus service could help increase efficiency and could be completed fairly quickly and require fewer funds than, say, laying rails. And as my colleague Alana Semuels wrote in a recent piece, more public-private partnership may be a solution that helps cash-strapped public systems increase their reach. According to Kanter, the problem has to be addressed, and quickly, especially in the face of growing economic disparity. “We need to think about how important forms of transportation are to the economy and quality of life. And we have to reinvest.”