[http://www.wired.com/wired/archive/12.12/traffic.html?pg=1&topic=traffic&topic_set= Roads Gone Wild] - roads with no signs make drivers drive slower so more safely.  I think this is just effect of the unexpectedness of the circumstances - people have to switch off their driving habits.  As soon as thay accustom to the situation they will develope new driving habits and I am sure the situtation will go back to the previous state (or perhaps I am not that sure, but I feel they did not think about creation of automatic habits too much).