The car is a very specific detail and it is doing a lot of work in your message.
What you are describing is the only place in your day where nothing is required of you. Not performance at work, not being available at home, just a sealed few minutes between two sets of demands. Feelings tend to arrive in the first gap they are given, which is why yours arrive there rather than somewhere more convenient.
So the crying is less a symptom than a location. The more useful question is what is being held for the rest of the day, and what it costs to hold it.
On the guilt: having a good husband and good children does not disqualify you from being depleted, and the two are not in competition. Guilt is common in exactly this situation, and it functions to keep the whole thing unspoken, which makes it heavier.
This is very workable, and people are often surprised how much changes from naming it once out loud. You do not need anything to be wrong with your family in order to bring it.
This is general information in reply to a public question, not advice about your own situation, and it does not create a client relationship. If you are in immediate danger, contact emergency services.
