I have just had my blue badge renewed after completing the online form for Dorset. I stated that when I don't feel able to walk more than 50m at the outset, I don't go out alone. I then explained the nature of PD is that while I'm out the meds can go off and i need to know my car is relatively close to shuffle back to, so I can suffer the more extreme symptoms in relative privacy, while I wait for my meds to kick in again.
This appears to have got the message across that for PwP our cars are as much a safe haven as mere transport. I received the email confirming renewal within 24hrs.
Of course, the real price of timing meds so you can drive to go out alone is at 2.30 am your tremor keeps you awake as you've had to adjust your meds timings to stave off the ever increasing number of pills used up before your monthly script runs out early. But that's a whole other topic.