BACKGROUND

Current accessibility guidelines in the U.S. such as the ADA-ABA Accessibility Guidelines (1), adopt a very simplified model of reaching ability that characterize reach in terms of six discrete scenarios, three depicting forward reach and three side reach. Accompanying each of these conditions is a threshold or limit for permissible maximum high reach and minimum low reach. Designers are then required to identify the most applicable condition(s) from these six scenarios and comply with the corresponding reach limits. The assumption is that tasks requiring reaching or grasping, if performed within these tolerance limits, would be successfully accomplished by most users, particularly mobility device users who often have restricted reach capabilities.

A direct benefit of the current prescriptive approach is that it provides a simple framework for conducting an objective assessment of a particular design for code compliance over a wide range of tasks and environments. The downside, however, is that the influence of key design parameters on reach performance, which have complex relationships, remains obscure to designers and hence neglected in the design process. Although prescriptive measures may be necessary for establishing baseline legal requirements, they do not provide much information to help designers (a) determine where to locate objects and devices in order to optimize accessibility, and (b) explore design options beyond minimal requirements, particularly when designers have the flexibility to do so. For instance, in the absence of performance data it is difficult to objectively evaluate two or more ‘code compliant’ design alternatives for inclusivity, without conducting expensive user trials or relying on the designer’s experience.

RESEARCH QUESTION

This study involved the measurement of maximum reaching abilities from wheeled mobility device users that were able to grasp a cylinder and could reach at least to shoulder height, using environmental user simulations and three-dimensional (3D) measurement methods. These efforts were directed towards developing a comprehensive research database on the anthropometry and functional capabilities of adult mobility device users in the U.S. (2). The objective of this paper is to describe the impact of reach height and obstruction depth on reach performance in the context of existing ADA-ABA Accessibility Guidelines, and the potential for reach performance-based tools in design.

METHOD

A total of 320 mobility device users that relied on wheeled mobility devices as their primary means of mobility participated in this study. Sixty-three individuals unable to perform a functional grasp and reach to the shoulder were excluded due to their lack of functional reach, as we defined it, resulting in a sample size of 257. The sample comprised of 157 manual chair users (61.1%), 79 powered chair users (30.7 %) and 21 scooter users (8.2 %), and included 97 (37.7%) females and 160 (62.3%) males.

Functional capability of the preferred arm was assessed using a portable apparatus consisting of five height-adjustable shelves. Shelf heights were set at the highest and lowest vertical free reach heights, shoulder (acromion) height, and two shelves each mid-way above and below the shoulder height for each participant. For safety reasons, the lowest possible shelf height was restricted to an arms length below shoulder height. Participants reached and placed an empty cylindrical canister of 75 mm [3.5 in.] in diameter and weighing 56 grams [2 oz.] at the maximum possible distance on each shelf. The point of maximum reach was digitized in 3D using an electromechanical probe along with a set of points used to construct a static 3D digital model of the individual and mobility device (3).

Three different reach directions (forward, side and an intermediate 45 degrees) were tested producing fifteen maximum reach data points. Reach envelopes constructed from these points were then superimposed on the 3D model of the individual-mobility device system allowing for distances between any pair of digitized landmarks and reach coordinates to be computed, e.g. from the most leading edge (anterior-most) or the lateral-most point of the person or device to the point of maximum reach. A computational procedure was used to obtain the reach range i.e. the upper and lower extent of reach, for each individual by identifying where the 3D reach envelope intersected with a vertical reference plane.

Four different locations of the reference plane identified from the Accessibility Guidelines (1) were used for the current analysis, at (a) the anterior-most point which provides the vertical extents of unobstructed forward reach, (b) the lateral-most point of the person or wheelchair, to obtain vertical extents for unobstructed side reach, (c) 255mm away from (distal to) the lateral most point, and (d) 610mm away from the lateral most point. Permissible maximum high and minimum low reach heights at these locations are summarized in Table 1. The percentage of individuals in the sample that were capable of reaching to various heights from the floor and obstruction depth in a given reach direction were then computed and plotted. It should be emphasized that these percentages depict the reaching abilities of only those individuals who could perform a functional grasp and reach to shoulder height.

Table 1: Guidelines for permissible reach height limits during forward and side reach (1)

Reach Condition	Reach Height Limits
	Max. High Reach	Min. Low Reach
Forward Reach - Unobstructed	1220	380
Side Reach - Unobstructed (max. 255mm obstruction depth)	1220	380
Side Rech (Obstructed (0-255mm obstruction depth; max. 865mm obs. height)	1220	-
Side Reach - Obstructed (>255-610mm osbruction depth, max. 865mm obs. height)	1170	-

RESULTS

Figure 1 (a-d) provides a summary of the results for the four reach conditions using horizontal bar graphs, stratified by mobility device type along with prescribed high and low reach limits. No individuals recorded reach heights below 400mm due to our safety restrictions.

Forward Reach - Unobstructed (Figure 1a)

Only 70% of all manual chair users, 52% powered chair users and 43% of scooter users who could perform a functional grasp and reach to shoulder height were able to reach to the permissible maximum high reach threshold of 1220mm (between 1200-1300mm) during an unobstructed forward reach i.e. if reaching to a target located at the plane of the anterior-most point. The highest values for percent capable were recorded between heights of 600-1300mm for manual chair users (70-77%), 700-1300mm for powered chair users (49-53%) and 800-1500mm for scooter users (38-43%).

Side Reach - Unobstructed (Figure 1b)

In contrast to forward reach, a far greater proportion of individuals demonstrated unobstructed side reach capability. The proportion of individuals able to reach to the maximum high reach limit (between 1200-1300mm) were 99%, 94% and 95% among users of manual chairs, powered chairs and scooters, respectively. Values for percent capable consistently exceeded 90% within the height range of 700-1500mm, with sharp drop-offs occurring outside this range.

Side Reach - 255mm Obstruction Depth (Figure 1c)

Compared to an unobstructed side reach, the percentage of individuals able to overcome an obstruction depth of 255mm (simulated by an offset of the reference plane by 255mm) decreased marginally, particularly among users of powered chairs and scooters. At the prescribed height of 1220mm, percent capable values dropped to 96% among manual chair users, 78% among powered chair users and 86% for scooter users. Accessibility was greatest between ranges of 700-1400mm among manual chair users (91-98%), 700-1200mm for powered chair users (80-87%) and 800-1400mm for scooter users (86-90%).

Side Reach - >255mm-610mm Obstruction Depth (Figure 1d)

Beyond an obstruction depth of 255mm up to 610mm, the ADA-ABA Guidelines recommend a decrease in the maximum reach height limit from 1220mm to 1170mm. When comparing the percentage of individuals able to reach a height of 1170mm at a 255mm depth (Figure 1c) vs. 610mm depth (Figure 1d) beyond the lateral-most point of the person/device, the percent capable drops considerably from 97% to 32%, 82% to 14%, and 86% to 33% among users of manual chairs, power chairs and scooters, respectively. The highest percentage of manual chair users able to reach over a 610mm obstruction occurred between the heights of 700-1000mm (38-41%), between 600-900mm for powered chair users (18-20%) and 900-1200mm for scooter users (33-38%).

DISCUSSION

The present report provides a brief evaluation of the ADA-ABA Accessibility Guidelines for reach ranges based on the findings of recent research aimed at assisting the revision of accessibility guidelines to be more inclusive of mobility device user populations. The research protocols employed in this study allowed us to assess four of the six reach situations included in the existing guidelines.

Reach capability differed substantially between forward and side reach directions during unobstructed reaches (Figure 1a vs. 1b) as well as across different obstruction depths during lateral reaches (Figures 1b-d). Despite markedly low percentage values for unobstructed forward reach and obstructed lateral reaches, most reaches were concentrated at heights between 600mm and 1500mm from the floor thus providing a broad comfort range that requires subsequent adjustment based on the specific design parameters and task context. While the sharp drop-off in ability at reaches below 500mm may be influenced by protocol restrictions on setting the lower-most shelf height, a similar drop-off was also observed at high reaches, a phenomenon that was more pronounced during side reaches.

Less than two-thirds of mobility device users overall could reach forward to the plane of their anterior-most point. Thus, tasks requiring a forward reach should provide toe and/or knee clearances to increase accessibility. In the absence of such clearance space, Figure 1b suggests that a lateral approach is preferred when possible. During side reaches with an obstruction, only about one-third of the sample that could perform a functional grasp and reach to shoulder height were able to reach to the maximum allowed obstruction depth of 610mm. This suggests the need for reducing the allowable depth to ensure greater accessibility. An extension of the current work presents a visual design tool for representing reach. Based on this tool, a maximum allowable depth between 300-400mm would ensure that at least 75% of mobility device users overall (n=257) could reach over the obstruction successfully (4).

While a number of important insights on the functional reach of wheeled mobility device users can be identified here, it is quite clear that current guidelines may result in an exclusion of a large percentage of mobility device users for the unobstructed forward reach as well as side reach with a 610mm obstruction depth. In recent years, designers and architects have increasingly adopted the concept of universal or inclusive design and are trying to accommodate people with functional limitations beyond minimum code requirements. The present paper focuses on evaluating the impact of the current ADA-ABA Accessibility Guidelines pertaining to reach based on anthropometry research in order to (a) assist in the revision of accessibility standards that are more inclusive of intended user populations, and (b) show how visual design tools and representations can help designers adhere to minimum standards but also accommodate a larger percentage of people in their designs.