Suddenly barking at cars

[anniehm]

Around a month ago my dog started barking at a car or van (from the boot of our car) at traffic lights maybe once on a journey, then it was every light, then last weekend it's cars behind us, in front of us - then today it on his lead (which he was on due to the fact I couldn't stand another barking journey as I had a headache!). Any ideas. He's 7 and never done it before. Have booked vet for Monday but as he hates vet she doesn't get particularly close. Definitely not hearing and think eyesight is good as catches ball fine.

Can call our trainer for help to solve but I'm worried about the cause, seems so odd behaviour. I'm wondering about neurological conditions, he's a collie. Thanks