Sometimes, a good TV zooms ahead, instant and unstoppable. Just ask Craig Bartlett, creator of the amiable new “Dinosaur Train” on PBS.

“When my son Matt was 3 or 4, he … had piles of dinosaurs and piles of trains,” Bartlett said. “I thought, 'If I made a show combining dinosaurs and trains, I'd have all the 4-year-olds.'”

So “Dinosaur Train” roared ahead – or should have. Instead, it chugged along; Matt is now in college and no longer in its target market. That “says something about the development process,” Bartlett said.

Maybe the delay was a good thing. In the 15 years since Bartlett thought of the show:

– He had a successful run as creator and producer of Nickelodeon's “Hey, Arnold.”

– PBS became a prime pre-school stop. It will launch “Dinosaur Train” with a four-show Labor Day marathon (starting at 7 a.m. on KHET), then run it each weekday.

– The Jim Henson Company returned to PBS, where the late Henson sparked “Sesame Street” 40 years ago. The marathon will be hosted by another Henson/PBS character, Sid the Science Kid.

– Computer-generated animation has improved. The Hensons have gone from puppets to traditional cartoons to CG. This show “is really a little bit too grand in scope” to do without computers, said Lisa Henson, co-CEO of the company her father started.

– And information about dinosaurs keeps changing. “It's a really cool, living science,” Bartlett said.

Scott Sampson, the show's resident dino-expert, offered an example: “'Jurassic Park' portrayed a velociraptor without feathers. A few years later, we find feathered dinosaurs in China. It turns out, probably all of those raptor dinosaurs were feathered.”

For consistency, director Steven Spielberg kept them featherless in his sequels.
Sampson has an alternative solution: Each “Dinosaur Train” includes two 11-minute stories, plus some live-action things he does with kids; if there are new discoveries, he can talk about them.

Then again, this is no documentary. Dinosaurs didn't ride trains, you know.

The story has a baby tyrannosaurus rex being adopted by a pteranodon family. He plays with creatures that a real carnivore would devour. “He's not going to eat them, because he loves them,” Bartlett said.

Still, there are basic truths here. “Kids are fascinated by huge situations,” Bartlett said. “They aren't huge themselves, so they love … the fact that these monsters walked the earth.”

They love trains, love dinosaurs; now they have both.