A few years ago, my grandfather gave up his car.

During the early years of his retirement, he'd been very active, volunteering at the local library and chauffeuring older folks who couldn't drive themselves. Over time, he slowed down, but remained independent — so much so that after a year or so in a retirement home, he stubbornly moved back into his own apartment. Though he was in his 80s, he didn't like the idea of being surrounded by — as he put it — "old people."

Eventually, his health declined to the point where it really wasn't safe for him to drive anymore. And though he used to take long walks daily, he could no longer traverse the vast parking lots and six-lane arterial roads surrounding his suburban Maryland apartment.

"As people have aged in the suburbs, they've been left behind"

Ultimately, he ended up largely stuck at home, entirely dependent on family to bring him food, give him rides, and provide simple human contact. In his final years, the car-based transportation system he'd relied on for his whole life really failed him.

His story is shared by millions of other American seniors, about 80 percent of whom live outside of urban areas. "As people have aged in the suburbs, they've been left behind," says Phil Stafford, director of Indiana University's Center on Aging and Community.

And the problem is growing. Americans are getting older: 14 percent are currently over the age of 65, and that's expected to surpass 20 percent by 2030. Modern medicine has extended people's lifespans — and people are spending more years with less physical independence. And yet a smaller percentage of seniors move in with family or to retirement homes than in the past.

"This is an unintended consequence of car-oriented planning," Stafford says. "We thought we were creating ideal communities for young families, but weren't thinking what it'd all look like 30 years down the road."

Sprawl forces seniors to drive (even when it's not safe)

Anyone who lives long enough will likely lose the ability to safely operate a car. But most states don't require driving tests for elderly drivers renewing their licenses.

Many keep driving for longer than they should — and that can be seen in data on fatal crashes:

Drivers are way more likely to be involved in fatal crashes past the age of 75. And for those 85-plus, the data is even worse than it is for teens.

This is mostly because in the event of a crash, older drivers are more likely to die from injuries than younger ones. But it's partly because older drivers have deteriorating vision and reaction time, which leads to more crashes overall.

This doesn't mean we should blame senior citizens for wanting to drive — it's an overlooked cost of a system that gives them no choice.

Giving up driving can leave seniors isolated

Once seniors stop driving, those who remain in suburban homes are marooned in an environment designed to be traversed by car. The most obvious problem, says Stephen Golant, a gerontologist at the University of Florida, is access to goods and services.

But seniors who are isolated also have worse health outcomes and lower life expectancies, even after adjusting for preexisting health conditions and other factors. This may be because they're less likely to get health advice and monitoring from family and friends and also because they miss the emotional benefits of regular human contact.

Isolation also means less tangible losses for both seniors and society at large. "Pursuing the new relationships and learning opportunities that give meaning to life becomes more difficult if you're isolated," Stafford notes. And those who aren't seniors miss out on the chance to benefit from the millions of senior citizens who can no longer drive, but are capable of volunteering or contributing to society and our personal lives in other ways.

Retirement homes partly solve this problem by providing contact with other residents and through shuttles for transportation to the outside world. But as part of the aging in place movement, fewer seniors are moving to them than before.

In surveys, more than 90 percent of senior citizens say they want to stay in their current homes as long as possible. Right now, if they want to avoid isolation, they're often forced to give that up.

Public paratransit shuttles are not enough

Some seniors have another choice: paratransit. Typically, these are systems that work in tandem with public transportation, providing shuttle service to people with disabilities to get them to a bus or subway stop. Public transport agencies are required by the 1990 Americans with Disabilities Act to offer this service to anyone with a disability, and about a third of its riders nationwide are over 65.

But for those who live in sprawling suburbs not designed to be serviced by public transit, trying to use paratransit can be difficult — if not impossible.

Paratransit is only required to serve people living within 1.5 miles of a bus line, a range that excludes most suburban dwellers. Those eligible have to make appointments well ahead of time and block out an entire day for travel, since shuttles typically arrive within two-hour windows, like cable TV technicians.

The biggest problem is that lots of transit agencies have been getting stricter in deciding who's eligible for paratransit, sometimes limiting it to people who use wheelchairs. "A lot of things that make you not a competent driver aren’t serious enough disabilities to qualify," Sandra Rosenbloom, author of a recent Urban Institute report on transportation for seniors, told the New York Times.

These restrictions share the same root cause: the cost of paratransit is ballooning:

That's partly because the systems are being asked to serve growing numbers of seniors spread out in the suburbs. Cash-strapped transit agencies underfund them, providing the bare minimum of service required by the law.

On a fundamental level, given the suburbs many seniors live in, paratransit might just not work well as a transportation solution, says Stephen Golant, a gerontologist at the University of Florida. "It's not clear that it's the most effective way of getting older people to the goods and services they need."

There are plenty of private senior-oriented shuttle services that help fill the gap. But they can be pricey, and don't work for those on smaller fixed incomes.

New solutions to senior transportation

The good news is that some communities and organizations are experimenting with new approaches.

Some are attempts to change development patterns in areas where seniors live. Stafford, for instance, is involved in planning a Lifetime Community District: an area that incorporates a series of neighborhoods in Bloomington, Indiana, arranged along a three-mile multi-use path. It will include grocery stores, doctors' offices, parks, and community centers that seniors can reach by walking or using a wheelchair.

There's also the increasingly popular Elder Village model, implemented by dozens of organizations in different cities. It allows seniors to stay in their homes, with a mix of paid staff and volunteers giving rides, delivering groceries, and organizing social activities.

"I think the Uber model is increasingly going to be important"

Other experts are optimistic that new technologies can help fill in the gap. "I think the Uber model is increasingly going to be important," says Golant. "All kinds of products and services will increasingly be at the fingertips of all people, including seniors."

He suggests that cities might start subsidizing Uber or Lyft rides for people who qualify for paratransit, as a more efficient way of allocating transit money. As an alternative, Stafford envisions nonprofit ride-sharing apps specifically tailored to seniors — and perhaps delivery of groceries and other goods as well.

More than anything else, self-driving cars could revolutionize seniors' transportation options. Widespread self-driving technology is still years away, but Google has programmed cars that can safely navigate a heavily mapped area in Northern California.

Some experts are skeptical that they'll ever be functional in real-world driving conditions across the country. But if they do, they could provide an easy means of getting around for people who can no longer drive — allowing millions of seniors to remain in their homes without becoming isolated.