“Nova” (7 p.m., PBS, check local listings) invites Tom and Ray Magliozzi, better known as Click and Clack from NPR’s “Car Talk,” to explore various plans for the “Car of the Future.” John Lithgow narrates.

Tom and Ray do a consistent job of disguising their MIT-educated smarts behind a barrage of laughter and corny jokes. They travel to Iceland, where the government is hoping to harness hydrogen fuel cells to make the island nation independent of imported oil. They also visit think tanks and laboratories where inventors are working on super-light plastics to make cars much lighter and batteries that enable cars to run more than 250 miles between charges.

Another expert explains efforts to bio-engineer special bacteria that can turn switch grass and other agricultural waste into ethanol. Like Rapunzel, these critters are expected to spin straw into gold. But they just haven’t been invented yet.

Tom and Ray barge into a Detroit car show to discuss the Chevy Volt, General Motors’ promised plug-in Hybrid. And they discover that it is still very much a dream car. Battery technology just isn’t there yet.

The “Car Talk” guys do a good job of talking with engineers, but they may be too logical for their own good. Everybody knows that car buying is completely irrational.

Back in the 1960s, Madison Avenue took an underpowered, underheated, unsafe and homely little car created by Nazis and turned it into “The Love Bug.” In our own time, advertising convinced soccer moms that they needed a top-heavy gas-guzzling SUV to feel “safe” while assuring their husbands that these same suburban status symbols had the potential to climb vertically out of the Grand Canyon – just in case they needed to do that on the way to the mall.

When Americans buy the car of tomorrow, they will have to be sold on it – seduced like their forefathers by the sorcery of advertising. And the technique for making lean and green seem sexy and powerful is a trick that has yet to be devised.

¢ Earth Day programming includes “Earth Report: State of the Planet” (8 p.m., National Geographic); “Big Ideas for a Small Planet: Gen Y” (8 p.m., Sundance); and “The Greening of Southie” (8:30 p.m., Sundance).

Tonight’s other highlights

¢ Is it just me, or has watching “American Idol” (7 p.m., Fox) become a chore?

¢ Coverage of the Pennsylvania primary (5 p.m., MSNBC, 7 p.m., CNN, Fox News).

¢ “Saturday Night Live: The Best of Chris Farley” (7:30 p.m., NBC) originally aired in 1998.

¢ It’s been a week since you last loathed them, but they’re back for a “Real Housewives of New York City” (8 p.m., Bravo) reunion special.

¢ Right now, the listings for “48 Hours Mystery” (9 p.m., CBS) remain a mystery.

¢ The strange case of the banker and the quarterback on “Law & Order: Special Victims Unit” (9 p.m., NBC).

¢ A mentally challenged man faces the death penalty on “Boston Legal” (9 p.m., ABC).

¢ Dahlia remains disillusioned on “The Riches” (9 p.m., FX).

Cult choice

A hack novelist (Joseph Cotton) finds more than he’d bargained for while searching for an old friend (Orson Welles) in postwar Vienna in the 1949 drama “The Third Man” (noon, TCM).