Pool Party

A road trip with Chris Martin. Aimless driving with Adele. Commuting with Jennifer Hudson. It could only happen on "Carpool Karaoke."

On city streets, amid a caravan of SUVs, James Corden conducts informal interviews and spontaneous sing-a-longs with some of music's greatest artists.

The Late Late Show segments — which premiere semi-regularly on the CBS program before going viral on YouTube — let fans see stars with their guards down, belting out their own hits — and covers — with gusto, Corden has carpooled with Mariah Carey, Justin Bieber and Elton John, to name a few, and the millions of online views show no signs of slowing.

"There's no [obtrusive] cameras, no lights," explains Ben Winston, one of the show's executive producers. "They're left on their own, as normal as they could be."

The carpooling portion of "Carpool Karaoke" has loosened to include alternate forms of transportation, including a tourists' bus and a tandem bicycle.

As for Hudson, "she was going to do a show that was being shot at [L.A.'s] CBS Television City, where we shoot," says Rob Crabbe, the show's other executive producer. "So [she and Corden] quite literally drove to work together."

But it's the karaoke that allows the guests — and Corden — to really shine. "It helps that he doesn't look like he should be a great singer, but he is," Winston says. "And of course he can rap as well, and he doesn't look like he should be able to do that either."

There are poignant moments, too: in one segment, Stevie Wonder calls Corden's wife and sings into the phone, "I just called to say, James loves you," bringing a tear to Corden's eye.

The host also sings along to each guest's songs with impressive lyrical accuracy, whether a classic by Rod Stewart or a recent hit by One Direction. But when Corden joins in on Elton John's "Your Song" with the icon himself, he deviates from the lyrics and exclaims mid-verse, "Oh, this is so much fun!"

Not that we need reminding.