With all due respect, the Yoshev Ohel is not the Rambam. He certainly is entitled to his opinion, and I am curious as to why he would say this. Unfortunately, I do not have access to the Sefer as of now. In any case, Davening while driving means at least one of two things: 1) The Tefilla is without proper Kavanah, and/or 2) The driver is putting his own life, as well as that of everyone else on the road, in mortal danger.
It is hard to imagine that his Tefilla while driving will be of superior quality to his Tefilla while pulled off to the side of the road, but even if it were, I have a hard time believing that this would be allowed. I would think that if it is so close to Shabbos that he is worried about Melacha, he is better off davening Maariv twice.