Baby cries in car at night!

So my little guy has been crying in the car only at night when it's dark. It's been going on for a while and we've tried everything but recently it's gotten so bad that a) he cries to the point of gagging and b) he starts to cry the second he's outside in the dark. Obviously it's a form of night terrors, and I've heard it's common but we've tried so much and I'm wondering if anyone else has experienced this. My husband and I usually take turns staying in with him if we can't get our babysitter, which honestly doesn't bother us because he's our baby and we love him so much but I guess what I'm looking for is to find out what other moms ( and dads) did that worked or when your precious child grew out of it if they did?? Any help would be appreciated!!!