Advice for Calming Cats during LONG Vet Trips?

i'm getting my 3 kittens (16wks of age) neutered. they're all getting neutered at the same time. 2 boys and a girl.

they'll be going on a 40 minute car ride to the vet. i got them a kitty cage and they'll all be together in it.

my poor kitties. they'll be so scared.

any ideas at all will be greatly appreciated

thank you