Elements of Access: Spontaneous Priority

by Wesley Marshall

 

 

SPONTANEOUS ROAD USER PRIORIZATION IN SHARED SPACE INTERSECTIONS (red line = 1:1 ratio of pedestrians to vehicles; hollow circles = pedestrian-dominated intersections; blue circles = vehicle-dominated intersections; circle size = higher level of modal dominance when conflict arose) by Wesley Marshall and Nick Ferenchak

SPONTANEOUS ROAD USER PRIORIZATION IN SHARED SPACE INTERSECTIONS (red line = 1:1 ratio of pedestrians to vehicles; hollow circles = pedestrian-dominated intersections; blue circles = vehicle-dominated intersections; circle size = higher level of modal dominance when conflict arose) by Wesley Marshall and Nick Ferenchak

Like we said last time, shared spaces are streets where all signs, traffic control devices, street markings, and separation of modes have been removed. This way of thinking forces all road users, no matter the mode of transportation, to take responsibility for their own actions and negotiate the space via all the other road users by means of eye contact and other social cues. This is in stark contrast to a conventional street design where modes tend to be separated and movements guided and controlled by traffic signals and the like. In the right context, the result of shared space is not chaos; instead, spontaneous order takes hold, resulting in a space often more efficient and safer than a conventional design.

Shared space is an often misunderstood concept. First things first; the right context is key. Shared spaces would not work everywhere, especially when the focus is mobility and high travel speeds. The surrounding land uses and the way that these buildings and activities interact with the street make a big difference. So does the mix of road users. A street dominated by cars would be hard pressed to function like we might imagine a shared space should.

Many people believe living streets and/or woonerfs to be synonymous with shared spaces. However, these street types specifically grant priority in the street space to pedestrians. A true shared space concept does not. Why? Because it doesn’t have to. In the right context, this prioritization occurs naturally. The above graph is from a recent paper I wrote with my doctoral student Nick Ferenchak. We analyzed data from 37 shared space intersections with high levels of interaction between pedestrians and vehicles and assessed which mode acquiesced to which when a conflict arose. When vehicles outnumbered pedestrians, while controlling for other design factors, the pedestrians tended to back off and cede the road space to the cars. However when pedestrians outnumbered cars, this prioritization spontaneously flipped. Now, the cars were the ones yielding to the pedestrians when a conflict arose. The red line in the graph above represents the 1:1 ratio of pedestrians to vehicles. What we call the modal dominance index is represented by the size and color of the circles. The hollow circles signify pedestrian-dominated intersections while the blue circles represent vehicle-dominated intersections. The size of the circle indicate a higher level of dominance over the shared space.

Many shared space designers are tempted to follow the living street or woonerf model and grant pedestrians priority in the street space, to the point where there is a call for what is known as a Pedestrian Priority Shared Space (PPSS). While such designs can be successful and find a multitude of benefits, putting up signs to grant pedestrians priority misses a key point of the shared space concept.   A true shared space in the right context doesn’t need those signs.