I say unusual in the sense of Japan seems to be the only one to have solved the issue of how do you transport 2 kids on a bike not with "big box" like the dutch and subsequently the entire western world but via 2 seats, they're apparently very popular over there as a means of transportation.
Bullshit, don't give dangerous advice. I was upright and going at a casual speed and got doored. Completely shattered my helmet, luckily I had one on.