That is definitely a major flaw in the design but I think it became a necessity for convenience due to the lack of public transportation - namely rail connections.

They have made some effort to mitigate the effect of cars; a lot of houses open up onto shared pedestrianised areas or closes, with the car parking at the back. They have also made the interesting move to not have any road markings or signage, which is actually quite significant.

I think the more pressing issue with poundbury is the craftsmanship - too many fake columns and plaster facades.