Jim Kenney's famous temper was on full view the day we strolled around Center City, looking at construction sites. More specifically, we were looking at construction sites where the sidewalks had been blocked. There aren't many things that make the Democratic mayoral candidate madder than having to cross the street because of a sidewalk closure - except when contractors treat the cordoned-off space as free parking.

"Tell me why that's necessary," Kenney sputtered as we reached the corner of 15th and Chestnut, where the 51-story W Hotel is going up. His face reddened, his eyes flashed. The two sides of the site were rimmed in chain-link fencing, ostensibly in the name of public safety. But the only thing the barrier was protecting was an assortment of glossy pickup trucks.

As a councilman, Kenney has evolved on a number of issues, like LGBT rights. But when it comes to sidewalk closures, his position hasn't budged. He hated them in 2008, when he introduced a measure intended to discourage developers from blocking sidewalks during construction, and he hates them now. Because the final legislation didn't make temporary walkways a requirement, he has taken to outing the most egregious sidewalk hogs on Facebook, as part of a personal crusade to liberate Philadelphia's pavements from the Jersey barrier.

But if Kenney becomes the city's next mayor, as seems likely, he vows to use the power of his new office to bring order to the streets.

Philadelphia pedestrians could certainly use such a champion. With so many high-rises and rowhouses going up these days, the city often feels like one giant - and treacherous - construction zone.

It can be hard enough for an able-bodied person to navigate the city's obstacle-filled sidewalks, hopscotching from one side of the street to the other to circumvent the barriers. But for the elderly, the blind, or the disabled, the gauntlet of sidewalk closures has turned walking into a game of Russian roulette. Philadelphia already has one of the highest rates of pedestrian fatalities of any Northeast city - an average of 19.2 percent of all traffic deaths - and yet installing walkways at construction sites remains optional here.

Of course, erecting a 50-story building on a narrow Philadelphia street poses its own kind of challenges. Developers often need to close the sidewalks just to make room to store materials or take deliveries. Annexing the space can be essential to creating a buffer between a swinging crane and the public. But, as Kenney argues, "there has to be a way to plan this so pedestrians and bicyclists aren't put in harm's way."

The biggest accomplishment of his 2008 bill was that it put a price on the public right-of-way by requiring developers to pay a fee for occupying sidewalks. It now costs $50,000 a year for each blockface that builders close off to pedestrians. The bill also included an incentive: The fee can be waived if builders establish a corridor for pedestrians in the street. It can be an elaborate, covered sidewalk shed, like what you see in New York, or a simple "cattle chute" formed with barriers.

Despite the new provisions, even the simplest walkways remain rare. The fees haven't even succeeded in getting builders to reduce the amount of time they keep the sidewalks closed.

It may be that the amount is just too low. After all, what's $200,000 to close four sides of a block when you're spending $1.2 billion to construct a new tower for Comcast?

But City Hall hasn't exactly shown leadership. The Department of Public Property didn't even bother to create a walkway for its current renovation project on the north side of City Hall, where there is an enormous amount of street capacity. Pedestrians are forced in a long circuitous loop across JFK Boulevard and around Dilworth Park, a walk that involves multiple street crossings. The excuse, offered by city spokesman Mark McDonald, is that a walkway would have necessitated closing one of the two turning lanes for 15th Street.

Given the choice between losing a lane of traffic or making pedestrians feel safe, it seems the car still wins.

What set Kenney off on his latest Facebook posting was the convergence of building projects this spring along 15th Street in Center City. There was a sidewalk closure on nearly every block between Dilworth Park and Locust Street, including dueling closures at the Chestnut and Walnut intersections. Even though 15th Street is routinely jammed with people, not one developer was compelled to provide a walkway. "At one point," Kenney said, "five out of eight sidewalks were blocked."

It isn't only high-rise projects that are responsible for the land grabs. Kenney was amazed that a three-house development on Arch Street in Old City kept its sidewalk closed for months, rather than make space for pedestrians. Rowhouse developments create some of the worst blockages.

Streets Commissioner David Perri said Kenney was "absolutely correct" and conceded that the city hasn't been able to monitor sidewalk conditions at every building site. "No one foresaw the uptick in construction," he said. It would help, he added, if his department had more inspectors to keep tabs on the builders, especially in the neighborhoods, but Streets only just received permission to add five staffers.

In addition to hiring more inspectors to check for abuses, Kenney's platform calls for adopting "Vision Zero," a set of guidelines developed in Sweden to reduce pedestrian fatalities, ideally to zero. Certainly, eliminating the sidewalk closures that force pedestrians into the street would be a good start.

Deborah Schaaf, a former city planner who now runs the pedestrian-rights group Feet First Philly, said it would take more than higher fees to make that happen. She would like to see the city follow the Washington, D.C., model, which makes walkways the default solution. If it's impossible to find the space because of site conditions, builders must submit a special request justifying why they need a sidewalk closure. Nashville and Seattle have just adopted that approach.

Compared to the alternative - a pedestrian population in constant danger - that seems like a cakewalk.

@ingasaffron www.philly.com/saffron