Towering over Boston’s Southeast Expressway, like a harbinger of back-to-school anxiety, is a billboard for the upcoming season of the CW’s Gossip Girl. Beside a picture of a steamy teenage kiss is a quote from a critic who declared the show “Every Parent’s Nightmare.”

It’s an attention-getter, an evil grin, a nontraditional appeal to the youth market. But it’s wrapped around a fairly traditional message: OK, hip young things. It’s time to watch network TV.

Yes, we now have iPod screens and YouTube, niche cable channels and caches of streaming video. But the old-school broadcast networks, the mass-media Big Five, are still banking on the idea that old habits die hard — even for young viewers. Particularly the timeworn couch-potato ritual of September, when America moves indoors and hunkers down in front of the television set.

That’s a surprising idea, in a way, in a year when everything was supposed to have changed.

For years, network leaders have buzzed about adopting the cable model of shorter TV seasons that premiere year-round. Once last fall’s writers’ strike stopped production in its tracks, many predicted an end to fall TV as we know it. NBC President Jeff Zucker proclaimed that his network was moving to a “52-week television season.”

And this fall’s TV lineup reflects some major changes in the industry, some of them permanent. Altogether, the networks have cut in half the number of new shows they’re introducing. Cable channels are putting their new series and old hits — such as Showtime’s Dexter, HBO’s Entourage and True Blood, and FX’s Sons of Anarchy — in direct competition with the network series, rather than in the relative safety of summer and spring.

Still, the networks have put significant thought and marketing dollars behind the new fall season. NBC peppered its Olympic coverage with relentless promotions of its lineup, reminding us how long we’ve waited for The Office to return. The CW has sent high school bands sheet music for the resurrected 90210 theme song. ABC has launched a tongue-in-cheek campaign for “National Stay at Home Week,” which happens to coincide with the start of its fall season.

“There’s still a rhythm to the television viewing season,” says Preston Beckman, executive vice president for strategic planning and research at Fox, which this week starts debuting its new series and airing fresh episodes of returning shows. “I don’t think there will be a massive erosion in ratings,” Beckman says. “I think things will get back to normal.”

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This year, networks didn’t order pilots at all, opting to pick up series based solely on their scripts. While CBS filmed pilots, executives say the timetable of approving scripts, giving notes, shooting, and editing was dramatically condensed. CBS has five new shows, NBC four. ABC has only two new series and is using the fall-season buildup to promote several series that debuted last year but disappeared after the strike.

What few new shows there are reflect some overarching trends. Sitcoms continue to be scarce across the lineup, though Fox will debut Do Not Disturb, a comedy set in a boutique hotel, and NBC has remade the Australian sitcom Kath and Kim. Other networks, too, are borrowing concepts from foreign markets: ABC’s Life on Mars is based on a British series, as are CBS’s Worst Week and Eleventh Hour. CBS’s The Ex Files is adapted from an Israeli show. And some other new series are remakes, from 90210 to NBC’s Knight Rider.

With fewer new series to promote, the networks have been advertising more strategically this fall. At the CW, programmers have focused on the target demographic of women 18 to 34, and the network is putting most of its marketing muscle behind what marketing chief Rick Haskins calls the network’s “lead dogs”: Gossip Girl and the new 90210.

ABC, meanwhile, is taking pains to promote its Wednesday night lineup of Pushing Daisies, Private Practice, and Dirty Sexy Money. All three shows premiered last year and never returned after the strike — and have been tweaked a bit in the off-season, with such changes as the addition of Lucy Liu to the Dirty Sexy Money cast and the toughening-up of Addison Montgomery, the Private Practice central character.

NBC is trying to build similar buzz around three returning series that had shortened seasons: Life, Lipstick Jungle, and Chuck. The network is also promoting a three-hour premiere event for Heroes, the supernatural series that never returned after the strike. And some new NBC shows, such as the Christian Slater vehicle My Own Worst Enemy and the Robinson Crusoe update Crusoe, will be previewed online, via Yahoo and Hulu.com.

The networks’ longstanding skittishness about new technology has all but disappeared. Nielsen has started to measure growing DVR use with its live-plus-same-day ratings. And the battle over whether to make shows available online is largely over. A short-lived CW experiment last spring — removing episodes of Gossip Girl from the network’s website — ended quickly and quietly, after tech-savvy younger viewers made it clear that they could find ways to download the series illegally.

“You’ve got to listen to the consumer and understand what their media consumption habits are,” the CW’s Haskins says, “and I think you have to be in line with them.”