I agree with the others, and I will take it one step further. Not only did you do the right thing in saving the injured person, and also in telling your BS, but I think the biggest accomplishment here is simply the fact that, after all this passed, you are going back and questioning yourself, your motives, your actions, and holding yourself accountable to all of those things.
In my personal opinion, the "no being in a car with another male" rule seems like a prophylactic of sorts. The rule probably exists because you cannot be trusted to do the right thing. In other words, you are the same person with the same vulnerabilities, and so the rule serves as protection from your nature and poor choices.
What you did today was something that represents change. You showed empathy, compassion, responsibility, thought of your husband, of the injured person, and most of all, thought of the consequences of your actions and how they would affect those around you. You didn't act out of selfishness, you put the needs of others before your own, perhaps even to your own detriment. And even though your husband acknowledged and approved of your decisions and actions, you still are "owning" your choices, and making an effort to reflect on them and analyze them so that you can learn from them, and verify that what you did was the right thing to do, the right way to feel, the right way to think.
While I cannot speak for your husband or any other BS's, I would think that this is what most would want to see in their WS's. Anyone can follow a rule, doing so does not make you a safer or healthier person to be around. During your affair, you did not consider other people, the outcomes, the consequences. You acted selfishly instead, and did not own your actions.
Today, by reflecting back on your choices and actions, and by discussing those thoughts and actions both with your husband and with friends (SI) I think you have demonstrated change. Actions being louder than words and all. You took ownership of your choices, and took steps to make sure they were the right ones. And had they not been, I get the impression that you would have made changes to yourself for the future so that you would get it right next time. So... brava. It's just my personal opinion, but I think this was a really good day for you.