These hierarchical distinctions of road types become clearer when considering the recommended design specifications for the number of through lanes, design speed, intersection spacing and driveway access. As the number of lanes increase from 2 to 4 and then 6 and, correspondingly, the operating speed from 40 km/hr to about 60 km/hr, the intersection spacing increases from a 90–200 m range to its double (200–400 m). Similarly, the restriction on driveway access becomes more stringent and, in effect, impossible in the case of a required raised median for boulevards and multi-way boulevards. Thus a multi way and simple boulevard (corresponding to the functional definition of arterial) are deemed to perform their mobility function better when access to them is limited to intervals between 200 and 400 m, that is every 3 to 5 normal, 80-m-wide city blocks.