Puppy Fearful of Outside – how can we help him?

We got a 4 month old rescue puppy just over a week ago. He’s overall doing very well only a few inside accidents, he’s signaling us by walking to the front door, and is willing to go about 30 feet from the front door to do his business. But he is obviously afraid outside, any people or noise or car passes and he wants to bolt back in. He is getting a little braver day by day and we never force him to go beyond where he is comfortable. He’s great in the car so we’ve driven him a couple places and let him observe from the safety of the car while giving him treats and not making him get out.

I guess I’m wondering is there anything else we can do to help him? He will need to go places soon like the vet, puppy training classes but he will not get out of the car. Unfortunately we don’t have a yard just a back patio area.