The problem arose when planners made blanket decisions, applying the criteria of speed and efficiency to all streets. Distances between points of interest grew, parking lots occupied valuable real estate, and Main Street disappeared as the automobile, not the pedestrian, became the “owner” of the street. It has become so prevalent, that much of modern planning today is aimed at reformatting these streets from the scale of the automobile back to the scale of the pedestrian.
via opinion: THE SEGREGATION OF THE STREET — An Architect’s Perspective.
When a street is shared, all users of the street must have a heightened sense of situational awareness. The requirement for every user of the street to be situationally aware will lead to caution and therefore safety. Designated lanes reduce the need for this situational awareness, providing people with a false sense of security while in their lane. Streets designed to demand situational awareness may not be the easiest, nor the fastest means to travel, but provide a safer environment for every mode of transportation on the street.