You could practically hear the ka-chings reverberating down Philadelphia's East Market Street in 2011 when City Council designated the corridor a "special advertising district." The measure turned the walls of buildings into gold by allowing giant digital billboards that can flash lucrative ads every few seconds.

But City Council, ever eager to accommodate the billboard industry, proved overly generous, and last month, PennDot informed the Kenney administration it was reasserting state control over the street's digital signs. At the very least, PennDot's takeover means those ka-chings are going to be sounding less frequently.

PennDot had sent the city multiple letters over the last 10 months, warning that fast-changing digital displays - like those atop the Lit Bros. building - were creating dangerous conditions for motorists, in violation of federal highway standards. Yet, as Deputy Managing Director Brian Abernathy told me in an interview, those letters went unnoticed and, therefore, unanswered. Perhaps the city was blinded by the lights?

With no response from the city, PennDot decided to act Sept. 8 by formally taking back regulation of the state highway.

That might not be such a bad thing, actually.

A little history is in order. The creation of the sign district sprang from good intentions: the desire to bring Market Street's retail back to its glory days. Once a miracle mile lined with grand department stores, the stretch between City Hall and Independence Mall had devolved into a shabby strip weighed down by the gloomy hulk of the Gallery mall.

In 2010, Councilman Frank DiCiccio came up with the idea of creating a Times Square-style sign district to encourage property owners to modernize their buildings. By plastering their walls with digital ads, the thinking went, the owners would be assured a steady stream of revenue that could be used to finance renovations. The only stipulation was that each building owner had to invest a minimum of $10 million before qualifying for the signs.

Viewed purely as a development incentive, there is no doubt the advertising district has been a roaring success. Three major redevelopment projects are now in progress: the Gallery renovation; the construction of the massive, mixed-use East Market project at 11th Street; and the Lits renovation.

But from a quality-of-life perspective, the sign district is a disaster in the making.

Although so far only Lits has installed large video displays, the changes over the last five years have already taken the corridor in an unexpected new direction. East Market Street isn't just getting better shops; it's being transformed into a residential neighborhood. Who wants to live in a place where digital signs cast a nightclub glow into your living rooms 24 hours a day?

At this point, only the National Real Estate Development Co., which is reconstructing the block between 11th and 12th, has included apartments in its project. But Lits and the Gallery have floated proposals for similar high-rise residential additions on top of their buildings.

Meanwhile, the corridor's new energy has also quickly spread outward. The entire east side of Center City, once dominated by commerce, is now bubbling with new development, much of it residential. It's hard to imagine Toll Bros. targeting a place like Jewelers Row for a luxury condo tower (not a good thing, actually) before East Market began its transformation. Nor would the new Collins apartments (a very good thing) on Chestnut Street have been built if the area's fortunes hadn't turned around.

All of this has taken city officials by surprise. Since being proposed, the sign district has been promoted as a way to create a Times Square-style destination capable of drawing tourists as well as shoppers to Market Street.

But that concept was flawed from the start. Times Square's physical conditions are entirely different. It's a crossroads where several streets come together, and Times Square's signs are viewed in the round from its pedestrian plaza. Its digital displays are also used to promote its signature industry, the Broadway theaters that dominate the area.

Market Street, by contrast, is a linear boulevard with a diverse array of attractions. But the biggest difference between the two is that Times Square is not in a residential area.

We're already seeing how the spread of digital billboards can harm Philadelphia's neighborhoods. After years of litigation, the city just approved the conversion of a paper billboard to digital at 11th and Vine in the Callowhill section. Peter Kendzierki, who lives in loft building just a few feet from the billboard, now fears the lights will make his apartment unlivable, and unsalable. They will also flood the new Rail Park on the old Reading viaduct with a constant barrage of ads.

The hope now is that PennDot can save Market Street from the city's advertising-mad impulses. The PennDot administrator overseeing the Philadelphia area, Matt Kulpa, told me the agency was still figuring things out, but it seems unlikely the agency will totally outlaw digital signs.

But future signs, he said, will have to be significantly smaller. They will have to be more widely spaced on Market Street - 500 feet apart, rather than the 100-foot increments the city's sign district allowed. Because of safety concerns, it's unlikely the signs will be allowed to host distracting full-motion videos. That's a good thing, considering 12th and Market is already among the city's most dangerous intersections.

Some city officials fear the tougher regulations could stifle development on Market Street. Why would that be the case when so many other neighborhoods are booming without their own special, cash-generating perk?

The sign district was really just another development subsidy, piled on top of the already generous property-tax abatements and state grants the Market Street projects have received. The only difference is that we would have had this subsidy flashed in our faces every time we walked down East Market Street.

Who would have thought the state highway agency would be the one to come to the rescue of Philadelphia's pedestrian realm?