@Lt.Caine Seatbelt can function just like helmet on motorcycles. Like when you get in and stand still, the character fastens the seatbelt, but if you hit the gas immediately, he doesn't. Maybe even use some animation for that.
P.S. How can I properly mention someone?
Great mod, definitely must have. In fact, I only used PLD for these features, IV-style vehicle exit and brake lights. What about adding more features? Like when you come to a stop, you keep holding the brake button and have brake light on. But if you want to go reverse you have to release the button and press it again. You could have seen this feature in modern racing sims and it has already been done for GTA SA (not sure about IV).