Possible improvement of 5V regulator protection

[yope]

The 5V regulator (TPS54328) can operate with a maximum input voltage of 18V (20V absolute maximum). While chances of exceeding that voltage are not that high most of the time, and for occasional connection to a car it will probably be fine, it can be improved.
There is the over-voltage protection circuit comprised of Q2, Q1 and D3, which intends to limit the input voltage to 17V approximately, but it isn't really necessary if a different regulator is used.

The best solution would be a full-blown automotive-spec regulator, like the LM53603. This chip can sustain even moderate load-dump conditions and would make this circuit suitable for permanent installation inside a car. D2 would need to be chose of type SMBJ39CA or similar. Also take care of capacitor voltages. Ceramic capacitors can usually withstand 40% overvoltage for a short while without damage. Also keep in mind the Vgs max spec of the output FETS (Q11, Q12...), they will need a zener diode to protect in case of overvoltage or disturbance on supply.

If that's too expensive, even the much cheaper TPS54339 might give a lot more head-room, and lets you avoid the OVP circuit (Q2, Q1 and D3), while also making the selection of D2 less critical.