Not to be too technical, but this idea of putting a deck on the Parkway East is way stupid.

I almost did a Danny Thomas spit-take with my coffee Thursday morning when I read that the Pennsylvania Turnpike chief suggested looking into elevated toll lanes over the Parkway between Downtown and Monroeville to ease congestion around the Squirrel Hill Tunnel.

Never mind that this sounds like an idea from the state Board of Uglification. How do you get around the tunnel?

Go over it and you destroy a nice old neighborhood. Go around it and you destroy a nice new neighborhood, the hundreds of homes that have been built in the past decade in Summerset at Frick Park. Then-Mayor Tom Murphy blocked a half-baked scheme for the Mon-Fayette Expressway in the same place 10 years ago, and the city since has turned the slag heap at Nine Mile Run into the Summerset boomlet.

But even if the tunnel weren't an issue, this idea from Joe Brimmeier, chief executive officer of the Pennsylvania Turnpike, would be reckless. Because betting that Pennsylvanians' driving habits are locked in the 20th-century era of cheap gasoline would be a multibillion-dollar bet on a lame horse.

Allen Biehler, the state transportation secretary, fired an unusually pointed shot at Mr. Brimmeier's trial balloon when I phoned his office.

"The days of just willy-nilly throwing out concepts of decks over the Parkway and bypasses of the Squirrel Hill Tunnel without a thorough analysis are over,'' Mr. Biehler declared in an e-mailed statement. "If someone wants to have incredible dreams about transportation, how about focusing on public transportation and doing things that make that option more viable for more people?"

Spoken like a man more worried about Pennsylvania's 5,935 structurally deficient bridges.

"We have to get that job done, as soon as possible,'' Mr. Biehler said, or the Birmingham Bridge will be the first of many to shut down for a time.

I forwarded Mr. Biehler's critique to Mr. Brimmeier's office. He called the next day to say the whole affair had "gotten way out of hand.''

He made nothing more than a suggestion and, even in his mind's eye, the toll bypass would break off well before the tunnel. The split would be around Bates Street in Oakland and tie into the Mon-Fayette Expressway, that never-say-dead project that is still shaking a cup in search of $3.6 billion.

Mr. Brimmeier is an affable guy, and he says if the Legislature doesn't like his idea it can go in the garbage "like a lot of other harebrained ideas in my life.'' But he doesn't want to drop the idea until "true professionals'' look at it.

When I suggested that an era of $3 and $4 gasoline might ultimately change driving habits to the point that tunnel congestion might ease by itself, he surprised me.

"I couldn't agree with you more,'' he said. "We obviously have a tremendous need for mass transit.''

How that squares with billions more in road construction, I'll leave to you. But with thousands of shaky bridges and an estimated 9,000 miles of road needing work, the last thing Pennsylvania needs is a road for an era we may never enjoy again.

Nearly every major infrastructure investment since World War II has been based on the premise that gasoline is cheap. But that's over. Unlike the 1970s, when price spikes were due to only temporary breakdowns in supply, oil is above $100 a barrel because of demand. The economies of China and India have been unleashed, and those genies won't go back in the bottle. The world needs oil like never before, and some major players see the barrel price going to $150 in a few years.

Even if that happens, Americans will keep driving. But the number of long-distance commuters will shrink over time. Driving an extra 40 minutes a day for a break on property taxes is a different calculation when gasoline is $3 or $4 a gallon.

It will be years before we know how that shakes out in Pittsburgh. Maybe older, walkable, streetcar suburbs become more attractive. Maybe more people work from home or live Downtown. Maybe residents of outer suburbs find more jobs out there. But kitchen-table conversations about potential moves will include commuting costs in ways they never did before.

The oil age began in Pennsylvania, in August 1859, when Edwin Drake drilled near Titusville and struck oil. The world changed that day and Drake's name wound up on plaques. But you'll also find scattered historic plaques about Pennsylvania's early 19th-century canals. The state built hundreds of miles of them -- and most were obsolete within a quarter-century because railroads took over.

Cars aren't going away, but upper-deck toll roads? Come on. Before we build a billion-dollar road with a great future behind it, Pennsylvania has thousands of crippled bridges to fix.