I recently read an ongoing forum discussion where many of the participants were lamenting how their building's Assembly Area involved them crossing a road to access it. I know that Australia's AS3745:2002 stated that where possible the crossing of roads should be avoided. That was a basic safety feature. I am confident when I say that passing motorists will have their attention distracted should they see a thousand people pouring out of a building, or even more distracted should there be smoke or emergency service vehicles attending. All that 'excitement' will cause motorists to take their eyes off the road.
AS3745:2010 however, has done away with this clause and for good reason. For almost every CBD of any major city anywhere in the world will have little chance of accommodating 1000+ people in a safe assembly area on the same block as the building that is evacuating. The hard reality is that to put some distance between the affected building and also access a plaza or park or other space big enough to allow large numbers of people to congregate, you are going to have to cross a road or two. When coaching emergency wardens I emphasize that emergency or not, crossing at controlled intersections in the legally prescribed manner, is what they are tasked with. Until the emergency services facilitate closing roads or stopping traffic to give assisted egress, motorists are a clear and present danger during evacuations.
A balance between safety, distance and the available landscape is constantly a challenge.