A micro-level approach to measuring the accessibility of footways for wheelchair users using the capability model
There are a growing number of people with mobility impairments who use wheelchairs to get around the built environment. This number is likely to increase in the future due to an increasingly ageing population combined with advances in medical technology which help to overcome some of the barriers to access that have hitherto prevented people from leading as full a life as they would have liked. Footways form an integral part of the transport network and therefore it is essential they can be accessed by all people. Currently, however, there is no well-defined method to measure the accessibility of footways for wheelchair users. One aspect of a footway is the crossfall - the transverse gradient designed to facilitate surface water drainage - which adds to a wheelchair user's difficulty when progressing along the footway. This paper first reviews previous research on measuring the effect of crossfalls on wheelchair accessibility, highlighting the need for a new approach. It then proposes the Capability Model as a starting point for this new approach. The model is updated and populated with an initial capability set chosen to measure footway accessibility across footways with three different crossfall gradients (0%, 2.5% and 4%). The focus is on the physical work provided by the user to the wheelchair in order to keep it travelling in a straight line. It is shown that in order to travel in a straight line when a footway is flat only a single principal capability is required: the ability to produce sufficient force over the required distance to overcome the inertia and rolling resistance and keep the wheelchair moving at the chosen velocity. When a positive crossfall gradient is introduced a second capability is required: the ability to apply different levels of force to the left and right sides of the wheelchair. It is concluded that it is possible to measure these two capabilities and these provide a good insight into the effect of crossfalls on footway accessibility for wheelchair users.