Driving Mrs Crazy

When you're driving behind someone who's crawling at 10mph in a 30mph zone, and you can't pass because there's traffic coming the other way, when you get more and more irritated, and when eventually an opportunity to pass opens up and you can leave that tortoise behind...do you zoom ahead thankfully, only to suddenly realise that you're doing nearly 40mph, and slow down sharply so that you're no longer breaking the speed limit? Or is that just me? 

If ever I get caught speeding like that - and I'm not a speed freak in general - it will be entirely and absolutely the fault of those "careful" drivers whose "safe driving" makes law-abiding people lose their temper and inadvertently ignore traffic laws. If going over the speed limit is breaking the law, doing 10mph in a 30 zone should be equally an offence!