Years ago I encountered a nut job on the highway while making a cross country trip with me mum. He and a woman driver were going about 40 mph in the fast lane and I passed them on the right without a thoght. The next thing I knew, the car came racing up behind me and this time the man was at the wheel. (In fact, he loomed over it -- he was clearly a huge man and he had thick glasses and a menacing demeanor.)
My mother had not wanted me to carry my 4-inch Security-Six in the glove compartment, so it was in the trunk, and this yo-yo started trying to run us off the road! He pulled up along side us and glared at us. He looked like someone out of a Grade B horror film, and while he didn't smash his car against ours, he'd make sharp swerves at us, then he dropped behind me and hung on my bumper tapping me at high speeds. When I slowed down, he'd slow down, and when I'd speed up, he'd speed up. I don't know what his intententions were, but it was clear that he had a screw loose.
I finally was alarmed enough to hit some high speeds, hoping to either lose the guy or attract the police (they're never there when you need 'em). I finally got in the right lane and was doing about 80 mph, him right on my bumper. As I was passing an exit, I suddenly took it and at that speed the wacko just kept going. I immediately pulled over, popped the trunk and retrieved my .357. We waited awhile and then got back on the highway. From then on, I've always carried my Ruger on cross country trips. It's stainless steel, it's a revolver and it will handle just about anything on the road. That's why the Highway Patrol was thrilled with the .357. It was great at penetrating car bodies and thick tires that .38s would just bounce off of. Short-barrelled .38s, at the time, couldn't even do much more than scratch the paint and leave a small dent.
A .357 Sig, .40 S&W and 9mm and 10mm would be okay in automatics, but a stainless steel revolver in .357 is my choice.