PITTSBURGH -- Follow 33rd Street in Pittsburgh toward the river and you'll eventually hit a dead end.

There, at the terminus, under a peeling stretch of elevated rail line, you'll find a trio of black-clad men standing guard in the middle of the roadway.

You'll look around at the automotive boneyards and gravel lots that surround you and wonder, maybe aloud, what brings them there.

But ask directly and you'll get little clarification.

Instead, the men will inform you they've been instructed not to talk.

You'll want to know why and by who, but remembering their oath and that steely look in their eyes you'll think better of asking.

Instead, you'll wander bemused back up the street, past the boneyards and warehouses, and into the surrounding Strip District. There, neighbors will tell you about the men and their reason for being, but also what they mean for a city in flux, for Second Acts in American life and all those inevitably left behind.

Pittsburgh, they'll say, is a changing city, which after decades of uncertainty has finally found its footing.

And, they'll add, the men on 33rd Street prove it may never be the same again.

'Changing at the speed of light'

That Pittsburgh is changing should come as no surprise.

Its rebound has been well-documented, steeped in superlatives and celebrated by presidents and Rust Belt revivalists alike.

It's gone from a smog-choked cautionary tale on industrial reign to a sleek and shiny municipal model; from "Hell with the lid off" to "Most Livable City."

All of this just decades after an economic collapse left a fifth of city residents unemployed and many more running for the door.

Now, the opposite is happening. With a surge in white-collar industries like tech, health care, higher education and energy here, Pittsburgh is poised to grow again. Unemployment is also down to around 5 percent.

All of this is good news, right?

Well, it depends on whom you ask.

While city leaders laud the turnaround, community activists fear the impacts for Pittsburgh's lower-income residents and communities of color, some of whom have been driven out by rising rents already.

The same tug-of-war is also being faced in Pennsylvania cities like Lancaster and Philadelphia, where working-class and low-income neighborhoods, as well as historical landmarks, continue to feel the squeeze of new and re-development.

But the suddenness of Pittsburgh's ascent remains remarkable. Between 2007 and 2012, rents were rising faster here percentage-wise than in New York City, long the high-water mark for real estate sticker shock.

In Lawrenceville, a neighborhood epitomizing the change currently underway in Pittsburgh, the average cost of a house almost tripled, from $46,267 in 2000 to $120,054 in 2013, KDKA-TV reported.

To this day, high-end condominiums rise out of the ground there seemingly overnight, turning what was a working-class enclave long before anyone cared into something altogether different.

"The only complaints I hear are about Lawrenceville, where they're saying the more expensive homes are pushing the older people out," Kerry Nauhaus said. Nauhaus works at a sports memorabilia store in the adjacent Strip District.

But it isn't just Lawrenceville. The neighborhoods of East Liberty, Oakland, Polish Hill and the Strip are all changing, too.

And while Mayor Bill Peduto has praised the drops in crime and bumps in investment that have sometimes resulted, the process remains an anxious one for many.

In the Strip, which one real estate agent described as "changing at the speed of light," neighbors have watched the influx of tech companies and the million-dollar condos that followed with what can only be described as cautious optimism.

For now, at least, they take solace in the fact that the remnants of Pittsburgh's blue-collar past and the seeds of its white-collar future both continue to reside there.

But then they look over at 33rd Street, and the black-clad men by the river, and sense that balance is shifting fast.

Silicon Valley - East

Walk through the Strip District now, and you'd be hard pressed not to notice the strange-looking cars moving around the streets there.

They sit at red lights, a jumble of whirring instruments and sensors bolted to the roof. They take off at green lights, no human hands around the wheel. And they round corners with wide-eyed passengers white-knuckling it inside. This is Uber's self-driving fleet, unveiled in Pittsburgh before the eyes of the world last September.

It is also a pivotal moment in the city's ongoing transformation, a new stage in what has alternately been described as an economic evolution or revolution.

Tech's role, in particular, remains central to that process in both the eyes of the public and Mayor Bill Peduto's office.

Since taking office in 2014, Peduto has made no secret of his desire to see Pittsburgh transformed into Silicon Valley - East. At times, his critics argue, this desire has led the mayor to overindulge private companies in an attempt to sell them on the city. The mayor's office, meanwhile, touts a long-term economic vision for Pittsburgh dependent on such companies as major employers.

Either way, tech's growth has been undeniable here both during his tenure and in the years leading up to it. (Google has been in town since at least 2006.)

By 2015, NextPittsburgh.com said the city was ranked sixth in the country in the number of tech companies funded by venture capital.

And between July of 2013 and July of 2014, while job postings in all industries grew by just 3.4 percent in Pittsburgh, postings for high-tech jobs grew by as much as 40 percent.

Those jobs also tend to pay more, on average, than their counterparts. According to the Pittsburgh Business Times, the average salary for tech jobs in Pennsylvania was more than $92,000 a year in 2015, roughly 82 percent higher than the average private sector pay here at the time.

In places like Pittsburgh, where the concentration of tech jobs is higher, that's bound to impact the real estate market -- and in some ways it has already. (Pittsburgh was also among the highest paying markets for tech workers in 2015 with an average salary of $82,788, a four percent bump from the previous year.)

"It definitely has made the market tighter," Maggie Jayson, a realtor, said of tech's growth in Pittsburgh.

Add to the mix an existing shortage of affordable housing and Pittsburgh's situation begins to resemble that of San Francisco's early housing crunch -- with some key differences, however.

In San Francisco, a massive tech boom served to drive up demand while zoning regulations served to prevent new construction and limit supply. The result was a housing choke point, one linked to sky-rocketing rents, a rise in Bay Area homelessness, micro-apartments and a fire at an illegally converted warehouse that killed 36 in December.

Pittsburgh zoning and code enforcement officials didn't respond to questions about whether they're seeing similar makeshift dwellings and illegal conversions as a result of rising rents here.

But members of the city council have repeatedly discussed -- and more recently taken action to address -- what Councilman Ricky Burgess calls Pittsburgh's "affordable housing crisis."

"We are having an affordable housing crisis, but it disproportionately affects the poorest of the poor," Burgess said at a December meeting.

"Market rate housing is eating up what used to be naturally occurring affordable housing, because the city is growing." Burgess did not respond to emails seeking comment for this article.

Ironically, it is a lack of affordable housing that has some in San Francisco plotting the move -- and in some cases the return -- to Pittsburgh.

Image via sfviapgh.com.

But while both cities face housing bubbles, there are some notable differences between the two.

For one, Pittsburgh's tech boom is nowhere near as large as San Francisco's. San Francisco's rents were also higher to begin with. Additionally, Pittsburgh has shown a better ability to add new housing stock, at least so far, which in turn helps keep demand from outstripping supply. (This was the key ingredient in San Francisco's crisis.)

There are, however, limitations to this ability.

Jeffrey Ackerman, managing director with CBRE in Pittsburgh, said they include the city's challenging topography, the occasional need for a zoning change and the length of time it takes to get projects permitted and approved.

But, for now at least, new construction continues across the city -- much, if not all, of it fueled by private investors and real estate equity investment firms.

"Right now we're very flush with capital. A lot of lenders and investors are interested in investing in new development in the city," Ackerman said.

"That's key to being able to build new supply."

But the question remains: Will that new supply simply compliment the existing market or come to redefine it?

Keep in mind that costs have already been rising here for years.

In Lawrenceville, for example, median home values jumped 45 percent between 2012 and 2016. City-wide, those values rose by 22 percent in that time.

On the rental end of things, John Petrack of the Realtors Association of Metropolitan Pittsburgh said prices began climbing as fewer people chose to own their homes following the stock market crash of 2011. That caused demand for rentals to rise, followed by prices. (Pittsburgh is currently ranked 22nd in the nation on a list of highest median rental prices.)

"Residential rents have climbed very significantly" since 2011, Petrak added using Lawrenceville as an example. "And commercial rent is not that far behind." In fact, tech's impact has probably been greatest in terms of Pittsburgh's commercial real estate market thus far.

And while it would be wrong to attribute all of this upheaval to one industry alone, it is tech's ability to further upend Pittsburgh's already dynamic real estate market which looms so large.

The reminders of this -- and tech's growing strength -- are everywhere here: Sometimes in the form of new office parks or developments, other times in the form of robotic cars circling the block, a jumble of whirring instruments and sensors bolted to the roof.

The next shift

Take 33rd Street into the Strip District and you'll find a neighborhood undergoing a sustained seismic shift.

You'll wonder what that shift might mean for this still gritty corner of a famously gritty city in 10 or 15 years' time. You'll wonder what it might then also mean for the city as a whole.

Walk a little farther and you'll see signs of a scattered backlash: "War on Google" spray-painted on a building near Nauhaus's store, for example.

But talk to the locals and old-timers and you'll learn that some are thrilled about the changes taking place and about the city's newfound relevance as a hub of tech and innovation -- as long as it doesn't adversely impact them. Others are indifferent, while a few pretend not to have noticed the almost Jetsons-era proving ground that's shaping up around them.

Those willing to acknowledge it will point to Uber's self-driving rollout here and the company's conversion of a former food warehouse by the river into a high-tech research facility -- the same guarded by those black-clad men on 33rd Street, they'll explain -- as signs of things still to come.

Pittsburgh is a changing city, they'll add, which after decades of uncertainty has finally found its footing -- and for neighborhoods like this one, there may be no turning back.