Hello! I recently made multiple pixel vehicles including a buggy, a hippie van, and a motorcycle. I took CC0 images from rawpixel, imported them to Piskel (My main pixel art tool), resized them, removed the background manually pixel-by-pixel, and cleaned them up to make the final product which I think look pretty cool! Here are the links to the original images:

https://www.rawpixel.com/image/3283789/free-photo-image-car-van-space

https://www.rawpixel.com/image/6037865/vintage-car-free-public-domain-cc...

https://www.rawpixel.com/image/6333242/image-vintage-public-domain-shape