That cooler temperature has got to be compounded by the lack of cars pumping out heat as well. But I wonder how such a design would handle large snow falls. Old northern cities in Europe don't seem as compact.
Yeah--my car has an outside air temp thermometer. Big streets are a few degrees warmer than small streets. The only reasonable cause I can see is the heat is coming from the other cars. (Note that this isn't even in heavy traffic.)
It's also the heat from the sun warming the asphalt/tarmac/concrete and that heat warming the air (which will continue long into the night -- "urban heat island" is I believe the name for the effect).
In the Phoenix metro, we moved to an area farther away from downtown that has more nature (there are large parks on two sides of our house). The temperature is regularly 5 degrees cooler here.