Filtered permeability is where types of traffic are restricted or ‘filtered’ by bollards, planters, trees, or even just camera enforcement. The most common type is where motorists are restricted but walking and cycling are allowed.
The benefits of filtered permeability include reducing rat-running, thus making streets less busy with cars, safer and more attractive which enables more trips by walking and cycling.
The location where filtered permeability measures are placed is referred to as a ‘modal filter’, ‘point closure’ or often negatively as a “road closure”.
The term “road closure” is inaccurate as filtered permeability allows for motoring access up to wherever the modal filter is placed, ie motorists can drive up to both sides of the bollards or planters etc, they just cannot drive through.
The term ‘low traffic neighbourhood’ refers to an area-wide system using filtered permeability measures.
Modal filters are seen as a new type of measure but their use in Dublin and elsewhere has been ongoing for decades — many examples on IrishCycle.com’s non-exhaustive map of modal filters were installed many years ago.
‘Drumcondra bollards’ filter during and after trial:
Grangegorman filter before and after trial
Examples from London
Examples from London show that modal filters can come in a range of shapes and sizes, including simple bollards, planters, traffic signs, trees, and even a bicycle share station:
Examples from the Netherlands
Often examples of filtered permeability in the Netherlands look like the measures have always been there, but, in older areas, this is usually not the case and most filters have been retrofitted.