City planner Jeff Speck has found the panacea for our ailing cities, something that could make even Detroit come to life again: walking.

In his new book, Walkable City: How Downtown Can Save America, One Step at a Time, Speck lays out something he calls his General Theory of Walkability. It’s not as platitudinous as one might think — Speck does own a car — but the book rests on the central point that cities designed for people, as opposed to those engineered for cars, will be the places of urban, demographic growth in the 21st century. If you build crosswalks, Speck’s theory goes, they will come.

“We used to call it New Urbanism — that’s scary. We called it Neo-traditional Design — that offended the progressives. People talk about density — we don’t even need to discuss that,” says Speck, who lives in Washington, D.C., and co-wrote the book Suburban Nation: The Rise of Sprawl and the Decline of the American Dream. “Reframing the whole argument under the rubric of walkability seems to be changing the game.”

OK. We’ll bite. Tell us, Mr. Speck, why it’s time to abandon our treadmills.

Q. Are you familiar with a band called The Proclaimers?

A. Yeah — “I would walk 10,000 miles,” or whatever it is.

Q. Would you walk 500 miles, Jeff?

A. To be the one that lands at your door?

Q. Yes.

A. I’m sure I have walked 500 miles in my lifetime, so yes, I would.

Q. Would you walk 500 more?

A. [laughing] I think I shall. I plan to.

Q. Now, you live in D.C. proper, correct?

A. I do, but I’m up at W Street which is far, far away from the heart of town. I can get anywhere I need to be in 15 minutes, just about, [on my bike].

Q. Do you have rules about walking and biking, versus driving?

A. It’s not a question of rules, it’s not a question of ideology. It’s a question of what’s practical, and on a daily basis I’ll make the decision whether to walk, ride my bike, take transit, or, God forbid, drive based on where I have to go and what’s easiest.

We’re gonna keep losing this argument as long as it’s some sort of moralistic hair shirt to ride a bike or walk. We just need to make places that cause people to find those choices both practical and pleasurable.

Q. But, you know, cities tend to be hostile toward two-wheeled machines without motors.

A. There are always going to be turf battles. … There are plenty of places where there’s just too much room for the car and everyone knows it, [and] when the public sees a traffic study that tells them their commute will not become congested because of my proposal, they are ready to go.

Q. Hey, you met your wife on a mass transit platform. Maybe we can find love in a hopeless place.

A. It was the MARC train that runs between Baltimore and D.C. And we were both at the BWI Airport. She had just flown in from Ireland, and I had just flown in from Miami. It’s a ride that now I would take a taxi because I’m older and less cheap, but back then it seemed the smart way to get to the airport.

Q. You bring up “bright flight” in your book — educated millennials flocking to cities — but I don’t think they’re moving in at such a clip that the rate of inner-city growth is eclipsing the rate of suburban growth.

A. Here’s what the Census showed us: Even the cities that comprehensively lost population between 2000 and 2010, they gained population tremendously in their innermost Census tracts. So what you have is first-ring suburbia, which happens to be within the city limits, is still losing out to outer-ring suburbia. But lots of people want to be in the heart of downtown. And so if cities’ physical boundaries were limited to their truly urban, walkable areas, we’d see nothing but shocking growth.

Q. Yeah, but aren’t those shocking growth rates just stemming from the fact that there weren’t many people living in inner urban areas in the first place?

A. The amount of growth seems shocking because so few people have lived in those areas recently, but in sheer numbers it’s still positive.

Q. How much is urban revitalization dependent on the political party in power?

A. The changes that are happening on the ground in many American cities now … [have] very little to do with any sort of political dominance at the local level. Many of the most wonderfully conservative, in the true sense of the word, achievements in American cities have been the work of conservatives. The Portland Growth Boundary was a Republican effort. I’m a bleeding-heart liberal, but I give credit where it’s due. I don’t see any relation between a state’s political climate, nationally or even locally, and people’s desire to see their downtowns have street life. My clients in Grand Rapids? Extremely Republican. My clients in Oklahoma City? Republican.

Q. Are you a fan of The Walking Dead at all — you know, zombies walking around all over the place?

A. I saw one episode. I thought the writing was horrible and the character development was unbelievable. But I love everything about zombies. I actually have regular daydreams about how to defend my house against zombies.

Q. In the event of a zombie takeover, is this the point where I can just burn gas, drive cars, and run them over?

A. I think any question of national defense or planning for the thousand-year storm, of any kind, works against urbanism. [In 1942,] the architect Josep Lluis Sert wrote a brochure called “Can Our Cities Survive?” And it compared what happens when a planeload of bombs drops on an urban area versus what happens when a planeload of bombs drops on a suburban garden city. It was one of many documents that was highly influential in the intellectual transformation that killed American cities.

Q. What’s the scariest thing you’ve seen built in a city?

A. Well, no one’s ever asked me that before.

Q. Just something that you looked at and said, “Have you read no Jane Jacobs at any point ever?”

A. Just yesterday I was in Cedar Rapids, and I was astounded to learn that Cedar Rapids has funded — and it’s too late to stop them from building — a beltway road. They’re about to spend tens of millions of dollars on a new outer beltway piece that’s gonna encircle the whole northwest quadrant of the city, even though we know, beyond a doubt, that any investment in urban highways is a sundering of previous investment in inner-city real estate.

Q. Why does this kind of thing still happen?

A. The reason we’re not making that much progress is that our cities, day by day, are not being designed by their leadership. They’re being designed, street by street, by the public works director, who believes he is doing his job by responding to public sentiment — and the biggest complaint you hear in American cities, day after day, is about traffic.

You know, we’ve lost 3.2 million Americans to car crashes — 3.2 million — and that doesn’t seem to have any impact on our policy making.

With just a couple of finger taps on my smartphone, I can purchase a beer via QR code or tell the people in city hall about a downed power line on my street. It’s better living through gadgetry — and now, a San Francisco-based business accelerator wants to put the same principles to work saving the planet.

Accelerators, common in Silicon Valley since the opening of Y Combinator in 2005, work like this: They lasso up a bunch of entrepreneurs, hand them thousands of bucks in seed funding, and ask them to grow or build companies in three months (hence the “accelerate” reference). Greenstart, founded in fall 2011, is the first accelerator program in the country that pumps dollars into cleantech — that is, technology that expands the use of clean energy.

Its founder is 40-year-old Mitch Lowe, a guy who, at 23, bailed on a “very boring finance job” he’d landed right out of college and founded his own marketing services agency — a proposition that turned out to be “a sort of a long failure,” he says. By 28, having watched another startup founder and sink, Lowe resolved to either get a real job or figure out how to actually launch a successful business. The result was Jumpstart Automotive Media, which handled ad sales for sites like Vehix.com and CarandDriver.com. After selling Jumpstart in 2007, he decided to bring the lessons he’d learned the hard way to companies that are committed to doing good.

“I have a passion for the environment and recognize that that is a big problem we have to face,” Lowe says. “But with a big problem comes a big opportunity.”

Enter Greenstart. Lowe says that large companies and the U.S. government are investing in big solar and wind energy endeavors — the major cleantech “hardware.” That leaves the “software problem” — figuring out how to trap, store, and shuffle energy — for smaller, entrepreneurial projects. It’s the “next chapter” of clean technology, he says, when the cost of solar and wind energy will steadily decline, and the importance shifts to what he calls the “networking of energy.”

It’s the smaller startups that Greenstart hands $15,000, along with $100,000 in a convertible note. A few examples:

• GELI, which has already been through the accelerator, has created software that helps with “distributed energy” systems, where electricity is generated with solar panels, etc., on rooftops and in backyards, rather than just at a handful of massive power plants — and where the battery in your electric car, for example, can be used to store energy when it’s not needed for use during time when electricity is in high demand.

• Smart Grid Billing is a company that tracks when electricity demand is highest (and therefore is most expensive) and dials back your home appliances automatically, saving you money on your electric bill and reducing the need for more power plants. It does this according to “consumer-specified criteria,” of course — so your TV won’t cut off in the middle of the Super Bowl.

Not all the companies Greenstart works with are wonky software applications — nor are they all related to the electrical grid. Scoot Networks is like Zipcar for electric scooters. RidePal is a commuter bus service that takes workers to and from offices in the suburbs — a school bus for grown-ups, only with WiFi and espresso machines. Spinlister facilitates peer-to-peer bike sharing.

Lowe looks for three things in a company before he writes a check: the team behind the company (including influential board members), signs of movement or progress, and whether there are customers willing to pay for what these startups are offering. After three months, startup founders show off during Greenstart’s Demo Day, when they present their products, and what those products do, on stage in front of cash-laden venture capitalists.

Humble beginnings, perhaps, but if Greenstart can lure young entrepreneurs away from making more photo-sharing apps, maybe the next Zuckerberg will figure out how to build cities that digest all their waste or feed people via gigantic vertical farms.

“You begin to show a spotlight on entrepreneurs that are doing really innovative things and … starting companies that reduce energy,” Lowe says.

Of course, Lowe’s no innocent optimist. He knows some of the startups that come out of his accelerator will fail, as many other startups do. The point, however, is to celebrate the “success stories” and “educate and inspire investors that [cleantech] is going to be a big category.”

Maybe that’s cause for excitement enough. In the meantime, I’ve got this great photo I want to share.

No surprises here: Boston physician Jill Stein bested second runner (and former sitcom star) Roseanne Barr by a 41 percent margin, winning 193.5 of a total 294 delegates. (One delegate was apparently split between Stein and a third candidate.) Stein, who ran against Romney in the 2002 Massachusetts gubernatorial election and won 3 percent of the vote, is running on a platform centered on her Green New Deal, an ambitious plan that would guarantee full employment of all Americans at a living wage, develop a green economy based on renewable energy sources, tax banker bonuses at a 90-percent rate, and legalize marijuana.

In her acceptance speech Saturday afternoon, Stein railed against a two-party system that she says offers little in the way of alternatives. The U.S. is “at the breaking point, for our people, for our economy, for our democracy, and for our planet,” she said.

Stein’s vice-presidential running mate will be Cheri Honkala, who ran for sheriff in Philadelphia in 2011. In her acceptance speech, Honkala talked about being a homeless, single mom in Minnesota. After she lost her apartment, she and her son lived in her car, then, when a drunk driver totaled that car, sought refuge in an abandoned house during winter. The Green Party, with its promises of jobs and health care for all, was a natural fit for her and her values.

“We are the new and unsettling force that Martin Luther King spoke for,” Honkala said.

Stein and Honkala addressed a crowd of a few hundred delegates crowded into the Chesapeake Room of the Holiday Inn on Baltimore’s Lombard Street. Representatives from all 50 states were there, including one delegate from Hawaii with a Chester A. Arthur-like beard who insisted the state was a sovereign nation. A majority of the crowd appeared to be middle-aged, although there were also college-age activists, like University of Wisconsin-Madison occupier Leland Pan.

The group slow-clapped to quiet the room, while delegates signaled their collective approval with the phalange-waving charm of spirit fingers. One speaker addressed them not as “fellow Americans,” but as “brothers and sisters.”

This, after a Friday night Green Party bash at an art and music venue in Baltimore’s Station North arts and entertainment district. Some 75 convention-goers enjoyed the musical stylings of eco-conscious band Woven Green, whose lead singer, Ashley Cash, sported frilly boots and an Earth-child headband. It was like an urban All Good Festival with booze, T-shirts for auction, and an arm-waving elderly man with a white ponytail who, given enough liquid lubricant, could have bested Beyonce in a “Single Ladies” dance-off.

But this was no Arab Spring. Even the Occupy movement was scarcely visible, save for a delegate from Delaware who demanded a mic check to quiet the room on Saturday, then led everyone in a “banks got bailed out, we got sold out” chant.

For a fledgling party, this year represents a small step forward. The Greens qualified for federal matching funds for the first time, but while party leaders can rile up a crowd of like-minded insiders, they seem woefully naïve when it comes to the politicking needed to build a national coalition and convince others outside the base to join in.

“The biggest challenge for any Green Party in any country is messaging,” said Richard Leckinger, a member of the Green Party leadership in New Zealand, where the Greens own 14 of 120 total seats in Parliament, making them third in terms of party representation. (Leckinger decided to attend the convention after realizing it coincided with a visit to his mother for her 80th birthday.) “You have to learn to talk to voters. I’m not sure the U.S. Greens are there yet,” he told me.

Of course, the Kiwis’ mixed-member, proportional electoral system, where people vote for both a party and a member of parliament, guarantees political parties seats in parliament even if they don’t win any electorate seats, but do win at least 5 percent of the party vote. (Still confused? Watch this video.)

Contrast that to our nation’s winner-take-all system, where a candidate with just 50.1 percent of the popular vote snags all a state’s electoral college votes, and the Green Party — which isn’t even currently tracked on Gallup’s 2012 election page — has a lot of work to do if it expects to have any impact on national politics.

Stein’s name is on the ballot in just 21 states right now, and her campaign lacks the money to purchase television advertisements. (The Green Party has no uber-rich super PACs.) She told the Boston Globe she’ll run a “traditional campaign,” traveling from state to state, and is counting on social media to spread the word about her candidacy.

Still, none of this seemed to matter Saturday. When Stein walked down the center aisle, assumed her place behind the lectern, and thundered in spite of her delicate frame, “This is the year we take our country back,” a Boeing 747’s worth of people rose to their feet in a standing ovation.

Now, if only some network other than C-SPAN had had its cameras rolling.

The Green Party came cruising into Baltimore on Thursday — er, wait, came riding into Baltimore. No. Had party members been able to walk and ride bicycles into Baltimore, I’m sure they would have, but even presumptive presidential nominee Jill Stein found herself riding in a jumbo jet in order to get here in a timely fashion.

But they made it nonetheless, and here they’ll stay for the next three days, holding workshops, fundraisers, and nominating their candidate for the highest office in the land. Barring any magical Roseanne Barr love-fest tomorrow at the nominating convention (the former sitcom star also tossed her hat in the ring), it will be Stein’s name on the ballot in, more than likely, 45 states by November.

In some ways it seems fitting that the Green Party chose Charm City as the location for its presidential nominating convention. Baltimore is sometimes forgotten to its bigger cousins, Washington, D.C., and New York City. It’s often seen as quirky and eccentric. And it’s easily stereotyped by the images we see in popular culture. (No, not every block is straight out of The Wire.)

Welcome to the Green Party, hanging on the heels of the Republican and Democrat parties, populated by an array of disparate interest groups, and written off by state election boards as unserious, tree-hugging, dove-releasing, organic-farming, grass-fed beef-ing … you get the point.

Stein, a Boston physician who was inspired to take up politics by environmental health epidemics, is perhaps a more mainstream candidate than the party has put forward in recent years. But still, it seems that nary a story can pass through the national media without the specter of her most prominent predecessor hanging overhead. Here’s the Times, yesterday:

While Ms. Stein barely registers a blip in national polling, experts point to Ralph Nader, the Green Party nominee in 2000, who was seen by many Democrats as siphoning just enough votes from Al Gore in one state, Florida, to tip the election to the Republican, George W. Bush. Nationally, Mr. Nader had captured only 3 percent of the vote.

Could such a situation unfold again?

Stein brushes off these fears. “We have 10 years of experience with muzzling ourselves politically, and it’s very clear now that silence has not been an effective political strategy,” she said in an interview with Grist earlier this year. “The politics of fear in fact has delivered all those things that we were afraid of.”

“The challenge for us is overcoming conventional communications, which is corporate-sponsored and would like to keep us down and out,” Stein told me in an interview Thursday night. “The political system is very engineered to silence any opposition party that’s not the corporate-controlled, big Wall Street power.”

Certainly the Green Party has made strides. For the first time in its 11-year existence, it has qualified for matching funds from the feds, up to donations of $250. Spirits have been buoyed by the Occupy movement that exploded onto the national media scene last fall, which was, to a large degree, a physical embodiment of the political philosophy of Greens: health care for all, forgiveness of college student debt, employment for everyone, an emphasis on environmentalism and green jobs, a reformed pathway to citizenship for illegal immigrants. Oh, and, legal weed.

“Everybody’s worried about a job, paying their college debt,” said Stein, who chose anti-poverty advocate Cheri Honkala to be her vice-presidential running mate. “This movement is vibrant and strong and unstoppable.”

Stein believes many people agree with Greens, and doesn’t understand, for instance, why banks get bailed out and students don’t. “A political campaign provides another rallying point for this very pent-up, frustrated energy that we can do better and the current system isn’t providing it,” she says. “It’s like a pressure-cooker now, and it needs an outlet.”

Whether that outlet is the Green Party, and whether people will be willing to cast their votes for Stein with the ghost of Ralph Nader – and the very real Mitt Romney — lurking about, remains to be seen. Perhaps, at the very least, her presence will prod President Obama to pay a little more heed to members of his “base” who might be tempted to jump ship. (In the last month, Obama has skipped both the Earth Summit and the national convention of the NAACP.)

This weekend in Baltimore may offer some hints as to what the coming months hold. The Greens have been hosting a series of workshops these first two days, about the Green New Deal, the green economy, and how to get money out of politics. Tonight they’ll throw a fundraiser at an art gallery and music venue in the city’s Station North arts and entertainment district. (Cover charge: $20.) Tomorrow will bring a string of speeches from national thinkers and activists, including 2008 vice-presidential nominee Rosa Clemente, and nominating speeches from Stein and Barr.

The turnout thus far would make anyone look askance at setting up more than two rows of chairs in a tiny press room, but organizers say there are 250 registered delegates, and expect up to 400 people to attend the convention.

As to why the Green Party picked Baltimore, Stein assured me that “a lot of thought” went into the decision. Something about a strong Green Party in the city. But if it’s here, it’s well hidden — or perhaps it’s just composed mostly of photosynthesis-loving organisms. The Maryland State Board of Elections revoked the party’s space on the state ballot last year because the Greens had failed to win 1 percent of the vote in the most recent election. Party members are now trying to collect the 3,000 signatures required to get back on the ballot.

Where are all those occupiers when you need them?

It’s true. An outfit called Global Innovation Company is distributing a line of bicycles bearing the names of foreign and American car manufacturers: Ferrari, Cadillac, Chevrolet, and Hummer, to name a few. The company was founded in 2002 by Katsuyoshi Ikeda, a man who thought younger cyclists would be more inclined to buy bicycles if they bore the logos of well-known, foreign car companies. Apparently no one told the Japanese that cars have lost their cool, because it seems to be working: Just last year, they bought 170,000 bikes flaunting the names of once-storied, combustion-powered four-wheelers.

The bicycles, manufactured with the carmakers’ blessing, are sold by the aptly named Import Bicycle Factory, which has a head office and shop in Yokohama, with sister stores in Kashiwa City and Kuki. Most of the lines — with the exception of Chevrolet — appear to include bikes for the whole family. Want Spartacus Atticus Thurston III to ride in style? Outfit him with this Ferrari kids’ bike with training wheels. Little Jimmy having issues with other kids in the playground? Have him roll up in this little Hummer (maybe take off the basket) and he can learn road rage years before other kids even realize their feet will one day touch the pedals. Gas pedal, break pedal …

Of course, Japan’s love of two-wheeled vehicular motion is nothing new. Bicycle parking lots the size of middle America’s Walmart Supercenters? Japan’s got ‘em. (Hello, 2 million bicycles’ worth of parking.) Ivy-covered above-ground bicycle storage containers? Check. (Let’s not even get started on their underground bike-parking contraptions.) Enough bicycles sold per year to outfit almost all of Los Angeles’s nearly 4 million residents three times? Yeah, Japan’s got those too. Schaaaa-winn.

But here’s the kicker: The car-bikes sold at Import Bicycle Factory, including the models proudly displaying American car manufacturers’ marks, are made in China. That’s no surprise, given that most bicycles in the U.S. are constructed by our friends in the Far East. Still, the irony of selling Hummer- and Cadillac-stamped bicycles, manufactured in China, to car-loving cyclists in Japan, while here at home GM tells us that we’re less manly if we ride a bike? That is worthy of some sort of award, especially as our own automobile industry continues to slump toward recovery.

Note to American automakers: Maybe it’s time to come out of the closet and start stamping your imprimaturs on bikes made here, stateside, for the growing bicycling public in the U.S. Trust us. Chicks dig that stuff.

Ehrenhalt is no starry-eyed urban triumphalist (like Harvard economist Ed Glaeser), but nor is he predicting cities’ imminent demise (see Joel Kotkin). In fact, compared to the prophets of urban boom and doom, he’s a whole heap of downright boring nuance. Think of him as your teetotaling uncle at the family Christmas party — the one who doesn’t want the eggnog spiked.

But sometimes the sober, analytical observers offer insights you don’t get from the prognosticators — and if what Ehrenhalt says is true, there are big changes in store for both cities and suburbs. So we called him up to learn more.

Q. Have you ever been on a riding lawnmower?

A. No. Have I missed much?

Q. No. You just kind of go back and forth in lines.

A. I’ve used almost every other kind of mower but not a riding mower. Not that sometimes I wouldn’t have minded sitting on a mower instead of pushing one.

Q. Well, the reason I ask is that we have this cultural ideal in this country — this image of having an acre or two that you can lord over. Do you really think Americans can learn to love city living again?

A. There are people like Joel Kotkin who are disappointed in cities because they lack the middle class population that he thinks cities should have. And therefore he is negative about the future prospects of cities. But the fact that young people, single people, couples, people with very small children want to live in cities is not a negligible event. The fact that people with four children and three cars and a gas grill don’t want to move out of the suburbs and into the cities doesn’t mean that something significant isn’t taking place.

Q. You call what’s happening here a demographic inversion, so it isn’t necessarily so much that we’re seeing on a wide scale a bunch of people flocking out of suburbs and back to cities.

A. A lot of people have gotten the mistaken impression that I’m predicting a mass movement of millions of people into the centers of cities. What we are seeing is a reversal in which the words “inner city,” which a generation ago connoted poverty and slums, [are going to mean] the home of wealthier people and people who have a choice about where they live, and the suburbs are going to be the home of immigrants and poorer people. And Census figures show that that’s taking place.

Q. It appears that my peer group — the millennial generation — is the main cohort moving back into cities.

A. I would say that’s right. There is a desire for urban life among the millennial generation, whether that’s life in the center of cities or life in town centers that are springing up in the suburbs. But some form of more walkable, urbanized living is part of the ethos of the emerging generation.

Q. With this inversion, aren’t we at risk of losing the racial and economic variety that attracts my generation to cities?

A. I think you’re going to have class segregation no matter what you do. It would be nice to have people of all classes living right next to each other in gentrified downtowns. That’s probably not going to happen. It is true that a gentrified area tends to become less diverse. Cities can’t solve all problems. They can certainly create affordable housing and cities have done that, but it’s a drop in the bucket.

Q. If poorer people are gradually moving to suburbs, does that mean that suburbs become the new slums? I don’t mean to be reductive, but doesn’t it cost much more to maintain suburban infrastructure — roads and transportation, for instance? Who pays for that?

A. I’ve never bought the argument that the suburbs were going to be slums, just that they would be ports of entry for people trying to make it into the middle class, rather than refuges for the affluent. It may be that with a lower tax base, some services would decline. But much of the infrastructure (parks, schools) is already in place.

Q. Do you see climate change affecting any of this? To make suburbs work in a carbon-constrained world, some major retooling is needed, but if the suburbs are increasingly the location of poor people, will anyone want to make the investment?

A. I don’t know much about this subject, but I don’t see global warming having a major effect on individual location choices unless it gets a lot worse than it is now.

Q. But the high cost of gasoline is something you do discuss in your book. What makes gas prices a factor now?

A. I’m not an expert at all in energy, but my amateur perception is that the average citizen feels that this spike in gas prices is not one that’s easily going to go away. We’re talking about what seems to me a demand-driven increase in the price of oil and the demand is coming from countries such as India and China, and I don’t see how that’s going to change. So it seems to me that we’re going to be living with high gasoline prices for the foreseeable future.

Q. Demographic inversion has big implications for cities and metro areas. What should government leaders or community activists do to prepare for it?

A. If the question is what should they do to encourage demographic inversion, then the answers are to promote mixed-use zoning, spend money on transit and policing, make sure there are parks for young children to play in, and support neighborhood schools. If you’re asking what they should do to ward off demographic inversion and create more diversity, I would argue that there isn’t much they can or should do. It’s very hard for governments to dictate settlement patterns. Segregation by class is a fact of American life.

Q. You grew up in Chicago, but now live in Clarendon, Va., which is like urbanized suburbia. What made you settle in Clarendon versus D.C. proper?

A. To be honest, my wife and I did live in D.C. for a while when we were first married, and then we moved to Virginia because her parents were out there. It really wasn’t much more complicated than that.

Once was that American cities competed to look more like Detroit, with gleaming lanes of highway stretching as far as the eye could see. Any more, it’s a race to imitate Copenhagen, the Danish capital where 36 percent of residents commute to work via bicycle.

So it seems, at least, when looking at today’s announcement by the League of American Bicyclists of the latest — and largest — round of official Bicycle Friendly Communities in the U.S. Some of the cities on the list will come as no surprise: Portland, San Francisco, and Chicago are here, as is Missoula, Mont., where 7 percent of residents bike to work, versus the 0.6 percent national average. But so are cities like Baltimore, Cincinnati, and Cottonwood, Ariz. Twenty-five more cities applied for bicycle-friendly status, but were denied.

The league hands down its Bicycle Friendly certification with a multi-tier, Olympics-like grading system: Cities can earn bronze, silver, gold, and platinum. The awards, which have been around since 1996, recognize cities that both promote cycling as a means of transportation and actively work to make cycling safer. A panel of national experts brought in by the league and local enthusiasts (bike shop owners, advocacy group leaders) assesses applications along five main criteria: engineering, education, encouragement, evaluation and planning, and enforcement.

The best cities, League of American Bicyclists President Andy Clarke says, have action plans in place to ensure that residents have opportunities to ride. They have city-sponsored bike rides, and networks of bike trails, lanes, and sharrows that connect them to where they need to go.

Louisville, Ky., is one city that’s done what Clarke advocates. In 2005, then-Mayor Jerry Abramson held the city’s first bike summit and vowed to make Louisville a gold-level Bicycle Friendly City by 2015. The city then set up bike facilities at traffic-heavy locations downtown, installed eight miles of striped cycling lanes, hosted community rides on Memorial Day and Labor Day, and raised $20,000 for bike education classes in 2006. In 2007, the city earned bronze-level certification one year ahead of schedule, and continues its cycling advocacy today.

Clarke says many of the winners are beneficiaries of some sort of cycling crusader or organization pushing hard for reforms, enforcement, and acknowledgment of bikers. “Having a champion like a mayor or city councilperson who set outs measurable targets and goals that you can hold yourself accountable to — that seems to make the biggest difference,” Clarke says.

One sticking point for the league is measuring how well local police enforce laws designed to protect cyclists. A recent study [PDF] conducted by Johns Hopkins University researchers found that cyclists in bronze-level certified Baltimore are routinely passed by vehicles traveling within the three-feet buffer mandated by law.

And while the latest round of awards is music to many bikers’ ears, “I will be the first to admit we have a long, long way to go,” says Clarke. Even Portland, Ore., which gets a platinum certification from the league, “would be a pretty crappy Dutch city when it comes to cycling,” Clarke says.

Forget riding your friend’s handlebars as he blindly navigates a crowded city street — unless you’re into that sort of thing. Thanks to a new peer-to-peer bike-sharing website called Spinlister, you may soon be able to rent a bike almost anywhere.

The brainchild of co-founders Will Dennis and Jeff Noh, a pair of 20-somethings living in New York City, Spinlister is like peer-to-per car-sharing services such as RelayRides, only for bikes. Bike owners snap photos of their two-wheeled trophies and post them to Spinlister’s online marketplace, along with the type of bike, the price per day, and the pick-up location. For those in search of a rental, it’s as simple as punching in their location, selecting the ride they want, making an online payment/reservation via credit card, and coordinating a meet-up time with the bike owner.

In addition to individual listers, Spinlister also works with bike rental shops. And while right now the service itself is only online in San Francisco and the Big Apple, Dennis says there will soon be nearly 1,000 bikes available for rent. And that’s just in the barely two weeks’ time since the official launch on April 1.

“We’ve got some great responses so far,” says Dennis.

Lest you think an online bike rental service screams flannel-wearing hipsters, let’s not forget what’s happening to millennials all over the U.S.: They don’t care about cars anymore. (See: the writer of this article.) As the cost of driving increases — gas, insurance, plus the autos themselves — and they spend more of their time in the online sphere, the youth of today are looking to alternative modes of transportation. Forget Rebel Without a Cause. Now it’s, “Hey, has anyone seen my bus pass?”

Or, with Spinlister: “Hey, I’m in New York for the summer and need a set of wheels.” That was Dennis’ predicament: He spent last summer in New York City — at a student start-up incubator, no less — but says there was nothing “that served a long-term rental purpose for me, and short-term [bike] rentals were expensive.”

Dennis has been working with Noh on Spinlister full-time since graduating from college in Los Angeles in December. The company takes a cut from each transaction: 12.5 percent from both the lister and renter, which goes toward credit card processing, the company, and Spinlister’s insurance policy to make sure you don’t get left in the lurch if some schmuck steals or wrecks your bike.

Of course, while bicycle theft is a real concern, Dennis doesn’t foresee it being an issue. “It’s way easier to steal a bike off the street than meet a person and not come back with it,” he says.

As of now, the two have been accepting listings in other cities — more than 80 different sites in 30 countries, which they’ll gradually roll out and make live over the next few months. They’re looking at possible expansion into Los Angeles, Portland, Chicago, Minneapolis, and Austin next.

And even though many cities are instigating officially sanctioned bike share programs, there’s not always a convenient pick-up and drop-off point — and most charge by the hour. And there’s something else, too, says Dennis.

The overarching goal of Spinlister is to create a community — to get bicyclists together with their own kind. Eventually, the company plans to build in mandatory Facebook connect and phone number-trading components to the online site. “I went out to dinner with a guy from South Africa I rented a bike to,” Dennis says.

Ladies … can I interest any of you in a bike-up theater date?

One Saturday in November, a few hundred volunteers descended upon parks and creek banks in and around Philadelphia to plant more than 2,000 trees. That day’s plantings were just a piece of a broader initiative to plant 300,000 trees in the City of Brotherly Love by 2015. And that initiative is but one part of a much larger program spearheaded by the Pennsylvania Horticultural Society that aims to plug 1 million trees into the ground across 13 counties in southeastern Pennsylvania, New Jersey, and Delaware. The mid-Atlantic is seriously putting the moves on Mother Nature.

As cities around the country jockey to be the King of Green, mayors and community organizations have been eager to claim their place as the next urban Johnny Appleseed. (Upon becoming mayor in 2008, Philadelphia Mayor Michael Nutter declared the city would become the greenest in America, and established an office of sustainability to show everyone he meant business.) But despite all the work days and feel-good volunteerism, urban forests are losing ground, in part because many, if not most, trees planted in cities die early deaths.

“Trees are so essential to our life, health, and safety,” says Caryn Bosson, a communications manager for the Los Angeles-based TreePeople, founded in 1973 for the express purpose of using trees to make cities more sustainable. Just one tree planted near a home has the potential to reduce heating and cooling costs by as much as $2,500.

If you can keep the tree alive, that is. “The planting of trees is a sexy thing to do — people want to plant trees,” say Ryan Allen, TreePeople’s tree care manager. “Getting them to come back within five years is tricky.”

That first five years is perhaps the most crucial part of a tree’s lifespan. A variety of factors can kill off an urban tree relatively quickly: Transplant shock to the roots of trees dug up at nurseries leaves trees susceptible to insects and disease; damaged tree roots, often the result of transplanting, can result in water stress where a tree loses water at a faster rate than it absorbs water. For city trees, vehicle traffic, air pollution, and street design can make healthy growth even more difficult. A report published in the journal Cities and the Environment [PDF] two years ago estimated that between 34 and 99 percent of young trees die off within the first five years.

A study published early this year by the journal Urban Forestry & Urban Greening [PDF] showed that tree cover across the country is declining by roughly 4 million trees each year. Of the 20 cities studied by the U.S. Forest Service, 17 had experienced net losses in tree cover, while 16 saw net gains in impervious cover — pavement, rooftops, and anything else that doesn’t allow rain to seep into the soil.

To stop this backsliding, organizations like TreePeople are trying to get volunteers to care for trees after the planting festivities are over. But that’s the unsexy part of urban tree planting. It’s far easier to get people to come out to plant if you have a gaggle of cheerleaders in tow, or if tree planting culminates in a huge event, like when the NFL planted thousands of Floridian mangroves in anticipation of the 2007 Super Bowl in Miami.

How do we make urban tree plantings more than mascot-filled publicity stunts?

“Our starting point around any involvement with trees is to start with the stewardship,” says Maitreyi Roy, the senior vice president of programs and planning with the Pennsylvania Horticultural Society (PHS). Before trees are even planted, she says, people are taught what it takes to keep trees alive. To that effect, the PHS has some 3,600 Tree Tenders, 2,500 in Philadelphia alone, who not only make annual checks of trees, but also teach volunteers about watering, pruning, and other tree-care techniques. Last year, Tree Tenders trained city staff and created a Tree Team for continuing tree maintenance in city parks. Also in use is a texting system that blasts volunteers with information on when to water trees in drought conditions.

“The goal here is to create a decentralized system so that the drive at the grassroots [level] fuels stewardship on an ongoing basis,” Roy says.

At L.A.-based TreePeople, community tree care teams serve a similar role. They educate volunteers, organized into Green Teams, on how to water, prune, and mulch trees, and then demonstrate at sites around the cities before helping Green Teams develop a maintenance plan according to a tree care checklist — pruning, watering, weeding, removing stakes and ties, and so on — specifically created for planting volunteers. In July, TreePeople kicks off its citizen arborist program, which will offer six weeks of “really in-depth education and planning,” Allen says, and is based on the International Society of Arboriculture’s certification program.

In the end, however, the simple trick to taking care of urban trees might be removing the gimmicks from tree planting altogether: Don’t let tree planters wash their hands of the whole affair after a few hours of work on a weekend afternoon. Allen suggests a solution, one that guides TreePeople’s involvement with the urban forest: “We’re not going to plant trees with you — schools, companies — if you’re not going to make the commitment to take care of the trees afterwards.”

Since gaining a foothold in the U.S. in the early 2000s, bolstered by pop culture (think: the opening scene of Casino Royale), parkour’s popularity has grown steadily, if slowly, in this country. Numerous informal organizations promote and teach this art of urban acrobatics, and a proliferation of YouTube videos show traceurs “freerunning” through the cityscape.

Still, many cities view parkour enthusiasts as lawless street ruffians, akin to skateboarders and street artists. In Manhattan’s Battery Park area, a “No Parkour” rule slaps practitioners with a $300 fine. In Hollister, Calif., anyone seen doing parkour is charged with trespassing. In November, the city of Margate, Fla., just north of Miami, banned the sport from all city parks, citing liability concerns. Mayor Pam Donovan said she thinks the sport is “dangerous and I’m never going to change my mind.”

Gradually, however, the sport seems to be gaining some acceptance — as a tourist spectacle, if nothing else. Parkour competitions featuring professional traceurs have been around for a few years: The Red Bull-sponsored Art of Motion events are big both in Europe and the U.S. But could street parkour, like street art, come out of the shadows and become an economic boon for cities?

This November, the city of Miami will find out when it hosts the first large-scale, international, amateur parkour event in the U.S. Some 125 freerunners from 40 countries will descend on the city for the three-day Cross Urban Scramble. A parkour arena in Bayfront Park will house singles and team competitions. Other activities will include a film festival, rock climbing, and an open forum about parkour insurance and safety.

Roch Nakajima, the co-founder of Parkulture, the organization sponsoring the event, says the goal is to bring a “global perspective” to the sport in the United States — already, teams from Palestine, South Africa, and Russia are scheduled to compete. But he also hopes the event will be accompanied by a substantial infusion of cash, from tourists and locals alike, earning it some much needed credibility among city officials.

Two recruiters from Cirque du Soleil will help judge the competition, Nakajima says, and Parkulture is currently negotiating sponsorships with two branches of the Armed Forces. Still, he admits, getting buy-in from City Hall is tough when “you’re kind of a new sport trying to establish yourself out there.”

Indeed, parkour aficionados have to do a lot of explaining.

Ask Derek Klein, the 25-year-old founder of Miami Parkour, to define his sport, and you’re likely to get hit with a one-sentence apophasis. “We’re not kids throwing ourselves off of rooftops,” he says.

Developed by a soldier’s son and in use by the French military for two decades, parkour “has deep roots in being able to help others,” Klein says. “If you’re climbing a wall in order to help someone who’s dangling off a ledge, you don’t want to act reckless and get injured.”

As unlikely as that might seem, this isn’t Homer Simpson and Ned Flanders doing somersaults atop cars driving on a busy freeway. Klein and the roughly 100 members of his group pull some remarkable stunts, and the serious ones claim to live by an ethic like those you find in martial arts.

“Parkour concentrates on this all around fitness idea of being strong in order to be useful,” Klein says, “and then to know your limits in order to know what you can do with out hesitation.”

In Europe, many cities make room for the sport in special “parkour parks,” similar to skate parks, where people can learn basic skills and hone their moves. Westminster, England’s park is purportedly the largest in the world.

On this side of the pond, Celerity Park in Converse, Texas, on the outskirts of San Antonio, was gunning for the title of first dedicated parkour park in the U.S., but plans have apparently stalled.

For now, the Miami area appears to be on the leading edge. In Margate, where officials banned parkour in November, Klein says that city officials have given traceurs a claim to an old roller derby rink, and are considering a proposal to turn it into a parkour park.

Whether it is a parkour park or an international competition, the major hurdle is insurance, says Nakajima, the organizer of the Cross Urban Scramble. “We are a litigious society,” he says. “There are no benchmarks for parkour that insurance companies have — no risk management plan.”

Still, Nakajima is optimistic that, in this age of X-Games-style stunt shows, he’ll find companies willing to cover his event. Perhaps then the sport will finally vault into the American mainstream. “As long as you get the insurance,” Nakajima says, “cities really don’t care.”