I like the vibe, but I would tighten it up a bit. I'm a minimalist, so I would phrase it like: Cars piled up Route 9. The drivers hid inside. Another bomb went off and they screamed. It's a strong setting. I would set it as quickly as possible and then get into some characters and story. Whatever you were about to say about shields and EMPs can be introduced through some dialogue. No reason to rush it.