Note that I’m not advocating an apology, but rather pointing out that now may be time to start considering the kid as a young adult whose opinions do matter.
If any other member of the family made a simple and reasonable request like “Hey, in the mornings I am kind of spazzed out and I find the car to be a bit of a high pressure setting. Do you think we could keep that kind of a neutral space and have our serious discussions in the evenings when there is more time to work things through” you would probably find that pretty reasonable and try to stick to that. I don’t see why you would suddenly disregard that kind of request simply because the asker is 14 rather than 34.
My suggestion would be to try to work this out on a semi-adult level. Remind him that you are not responsible for how his day goes, but that you are willing to work with him to find a better time to have these talks. Maybe come up with some kind of nightly routine- cups of hot chocolate or lemonade or something- that includes homework talk.
I’m only so passionate about this because my mother’s method of dealing with this stuff was to ambush me in the car on the hour-long drive to skating practice. We had a very different communicating style. She wanted to have long talks, completely working through the emotional aspects of the problem before figuring out practical solutions. I, on the other hand, needed a bit of time alone after a conflict to get past my defenses. Then could I begin to rationally approach the problem, acknowledge the other side’s point, and propose solutions.
As a result, these car rides became a time of dread. Even know, I get a lead feeling in my stomach just thinking about them. To me, it was my mom hitting me with all this emotional stuff when I could not escape. Backed into a corner with an hour ahead of me, I’d get immediately defensive. What happened every time is I’d keep defending myself until it got to yelling, then eventually I’d break down and cry, and finally we’d start talking about solutions. This happened countless times, until I eventually quit skating in part because the drive became so stressful. It took until long after I left home for our relationship to heal, and even today there is some residual distance and when I visit home I can’t shake the feeling that I’m about to get jumped with something.
A lot of that could have been avoided if my mom had just been willing to give me ten minutes to collect myself before starting a conflict. She’s not wrong and I wasn’t wrong. We just had an incompatible conflict style. In the end, it’s not what’s right or wrong that matters- it’s what works. Any couple having these kinds of problems would probably try a counselor to find a way of addressing issues that doesn’t lead to a breakdown. Living with a teenage kid really isn’t that different, you have to find something that works. And since the parent is the one with the power, that often means the parent is the one who has to change their approach. Of course they shouldn’t have to, but if they don’t want the same problems to keep happening, it’s still a good thing to consider.