Japan is designed with public transport in mind. Most everywhere in Japan is within train/bus/bike/walk distance. You don't need 4 lane high ways when there are maybe a few dozen cards on any particular stretch of the high way at any given time. I drove from Nara, Nara to Naruto, Tokushima via highway and saw maybe ten other cars on the highway. That's a distance of 174.5km; roughly a 2 and 1/2 hour drive. If I drove for 2 and 1/2 hours on any stretch of highway in California, I'd see ten cars every few minutes.
Less cars in the road, in general, means roads can be more narrow.
Japan is designed with public transport in mind. Most everywhere in Japan is within train/bus/bike/walk distance. You don't need 4 lane high ways when there are maybe a few dozen cards on any particular stretch of the high way at any given time. I drove from Nara, Nara to Naruto, Tokushima via highway and saw maybe ten other cars on the highway. That's a distance of 174.5km; roughly a 2 and 1/2 hour drive. If I drove for 2 and 1/2 hours on any stretch of highway in California, I'd see ten cars every few minutes.
Less cars in the road, in general, means roads can be more narrow.