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ACCESSIBILITY REQUIREMENTS FOR RAMP SLOPE: RESULTS OF HUMAN SUBJECTS TESTING

Jon A. Sanford, Molly Follette Story, Michael L. Jones Center for Universal Design, North Carolina State University

ABSTRACT

This paper reports the results of a study to evaluate the usability of the range of ramp slopes allowed under the current ADA accessibility guidelines. One hundred seventy-one subjects of all ages and using different types of mobility aids traversed a 30 foot ramp varying in slope from 1:8 to 1:20. Data was recorded for pulse rate, energy expenditure, rate of travel, distance traveled, and the location of rest stops. Findings show that among all subjects only a few manual wheelchair users had difficulty traversing all 30 feet in ascent, even on slopes as steep as 1:8.

BACKGROUND

Section 4.8 of the Americans with Disabilities Act Accessibility Guidelines (ADAAG) specifies that ramp slopes should not exceed a ratio of one inch in vertical rise to twelve inches of horizontal run for a maximum rise of 30 inches. Although this requirement is consistent with other accessibility standards, over the years there have been questions concerning the adequacy of the 1:12 slope as well as the maximum slope in alterations where ADAAG allows slopes steeper than 1:12 for rises up to 6 inches.

Although current standards for ramp slope and length have been based upon a considerable amount of research over the past 25 years, most studies used fairly homogeneous populations of young males with good upper body strength and stamina (e.g., Elmer, 1957; Canale, Felici, Marchetti & Ricci 1991). Recently, however, advances in medical sciences, increased survival of people from accidents, and development of new assistive devices have resulted in greater numbers of independent frail older people and people with severe disabilities. As a result, the validity of existing requirements for older users and users with more severe functional limitations has been questioned with increasing frequency. In fact, at least one study (Steinfeld, Shroeder & Bishop, 1979), supports this argument, suggesting that ramp slope vary between 1:16 and 1:20 based on a sample of individuals with more restricted functional abilities and a wider range of ages.

RESEARCH QUESTIONS

In order to develop recommendations for accessibility guidelines for ramps to be considered in future revisions to ADAAG, the study addressed the following questions: What are the maximum and optimum slopes and distances that individuals with different disabilities can traverse safely? What is the relationship between ramp slope and length? For people with what types of mobility impairments are these slopes and lengths appropriate, and does it vary by disability?

METHOD

Apparatus. A 36 in.-wide, 30 ft.- long, aluminum ramp with a triple row of tubular aluminum side railings (at 8, 21.5, and 34 in. was adjustable to seven calibrated slopes: level, 1:20, 1:16, 1:14, 1:12, 1:10 and 1:8.

Procedures. Two baseline trials (forward and back) with the ramp in the level position were conducted first. Following the two baseline trials, subjects were asked to ascend and descend 6 additional slopes (1:8, 1:10, 1:12, 1:14, 1:16, and 1:20), thus comprising a total of 14 trials. In order to minimize ordering effect, the slopes were presented in a random order.

Participants were instructed to traverse the ramp at a comfortable pace, pausing as needed and simulating the way they would typically use a ramp. At the end of each trial, pulse and oxygen saturation levels were recorded. When subjects' pulse and oxygen levels stabilized, they were asked to complete the next trial.

Data Collection. Seven dependent variables were observed for each ramp trial: total distance; total time; rest stops (i.e., number, duration, and location); pulse rate; oxygen saturation (i.e., energy expenditure); hazardous maneuvers (e.g., control of speed and occurrences of slipping); and assistance.

RESULTS

Sample. A sampling frame was established based on age and type of mobility device used. The sampling frame called for a sample of 192 subjects in six age categories using nine types of mobility aids -- manual wheelchairs; power wheelchairs; scooters; canes; crutches; walkers; prostheses; orthoses; and no mobility aid, but activity limitation.

Only subjects who were generally in good health were permitted to participate in the study. A total of 171 subjects representing 43 of the 51 cells in the sampling frame participated. Seven of the eight cells for whom no participants were found were single-representative cells, the eighth was a two-person cell. Older participants over 75 years of age accounted for the largest number (10) of missing subjects. However, because this age group was the largest in the sampling frame, 85.7% of the targeted number of subjects participated. By mobility category, subjects who used canes or crutches had the largest shortfall (14) from the sampling frame. However, this subgroup accounted for the largest single cell in the sampling frame (99). As a result, 85.9% of the targeted sample was tested. Finally, the ratio of males (41.5%) to females (58.5) remained true to the sampling frame (42.7% to 58.3%).

Distance Traveled. The sample as a whole had little trouble in ascent, completing 1164 out of 1181 trials (98.6%), and had even less difficulty in descent, completing 1179 trials (99.7%). However, the incomplete trials is examined by mobility category, 15 of the 17 (88.2%) were by subjects who used manual wheelchairs and the remaining two (11.8%) were by those who used canes.

Although the two incomplete trials by cane users appear to random occurrences and may be due to the effects of fatigue, about 10% of the trials by wheelchair participants were unsuccessful. Not surprisingly, the three steepest slopes accounted for 80% of the incomplete trials. Moreover, the same five subjects were responsible for all of the incomplete trials. One subject failed to complete all six slopes, two additional subjects failed to complete the three slopes steeper than 1:14, one additional subject failed to complete slopes greater than 1:12, and one additional subject failed at 1:8. Finally, it is interesting to note that the five the subjects who failed to ascend 30 feet were all women. Four of the five were over 65 years of age.

Rest Stops. Of the 1179 ascent trials only 24 (2.0%) involved the participant stopping to rest. Subjects who did not complete a trial stopped more often (1.24 stops per trial versus .01 per trial), and at shorter distances (7.44 feet for rest stop 1 and 12.83 feet for rest stop 2 versus 16.98 feet and 25.75 feet, respectively) than those who completed the trials. Moreover, slope did not to impact number, distance, and duration of stops.

Rate of Travel. The overall trend, with few exceptions was that speed decreased as slope increased from 1:20 to 1:8. Although the decrease in speed within each mobility aid subgroup was generally not significant, the downward trend for each is clearly shown in Figure 1. This is particularly evident within the manual wheelchair group where speed decreased by 50% between the level and a 1:8 slope. A second trend was the difference in mean speed across mobility subgroups. People with different mobility aids traveled at different rates of speed, regardless of slope. However, with the exception of manual wheelchair users, increased ramp gradient had the same effect on all subjects regardless of subgroup. Although slope did affect manual wheelchair users, the effect was equally evident across all slopes, not just the steeper gradients, as one might expect.

Figure 1. Mean Rate of Travel Pulse.

For the sample as a whole, there was almost a perfect linear relationship between slope and change in pulse (Figure 2). However, such a linear relationship does exist for any of the mobility aid subgroups. In fact, none of the ambulatory subgroups had significant changes in pulse at any of the seven ramp slopes tested. In contrast, manual wheelchair users had significant changes in pulse up to slopes of 1:14, indicating that slope had a greater impact on this group. However, the impact leveled out at 1:14 with no significant differences due to slope until 1:8.

Figure 2. Mean Change in Pulse

Oxygen Saturation.There were no significant differences in the mean measures of oxygen saturation either within or across groups. Not only is this surprising, but because exertion is really only evident when saturation begins to fall below 90% (particularly as saturation approaches 85%), the sample as a whole (with a mean range of 98.24% to 99.77% saturation) clearly did not exhibit signs of exertion. In other words, 30 feet at any of the slopes does not appear to be a strenuous task for any of the mobility aid subsamples.

DISCUSSION

Although not particularly surprising, the data indicate that none of the factors of interest in this study - slope, mobility aid, gender, and age -- had much of a bearing on subjects' ability to or amount of effort expended while descending ramps of any slope. However, a number of factors, most notably the interaction between ramp slope and manual wheelchair users had an impact in ascent.

Distance traveled is perhaps the most notable evidence suggesting that slope impacts performance by wheelchair users. Of the 151 ambulatory and "other" subjects, only two, apparently random cases (both involving cane users at shallow gradients), resulted in subjects terminating prior to reaching the top of the ramp. In contrast, only 85% of the participants who used manual wheelchairs were able to traverse 30 feet at a slope of 1:12, 80% were able to traverse 30 feet at 1:10, and 75% were able to traverse 30 feet at 1:8. While the percentage of subjects who completed the entire length at the two steepest slopes is higher than expected, the relatively large percentage of manual wheelchair users failing to traverse all 30 feet indicates that slopes steeper than 1:12 at distances of 30 feet is probably too difficult for this population. In fact, 30 foot distances between level rest stops at 1:12 may be too steep for certain segments of the wheelchair population, most notably those who are older and female. This is further evidenced by the increased number of rest stops required by manual wheelchair users in comparison to the rest of the sample.

When rate of travel is considered the data indicate that either the ramp gradients or the 30-foot distance, or both, are sufficient to dramatically impair subjects' rate of travel. However, whereas increased ramp slope tends to affect all of the ambulatory participants and those in the "other" subgroup equally, manual wheelchair users have a significant decrease in speed between the baseline and a 1:14 slope. However, the insignificant increase in rate of travel beyond a slope of 1:14 suggests that there is probably a minimum rate of travel that they must keep up to maintain forward propulsion and that rate was reached at a slope of 1:14.

Manual wheelchair users, unlike the rest of the sample, also experienced a significant increase in pulse rate between the baseline and a slope of 1:14. After 1:14 pulse change leveled out. This finding further supports rate of travel data, indicating that 1:12 or 1:10 may not be any more strenuous than 1:14. Moreover, when the oxygen saturation data is considered, a 30 foot distance is not overly strenuous, even at the steepest slope, thus suggesting that even though pulse rate hits a plateau, that plateau is far below total exertion.

In summary, the data suggest that 30 foot ramps, particularly those at slopes of 1:12 and higher, present some difficulty for manual wheelchair users, but not people who use other types of mobility aids. However, with the exception of a few older, female subjects, a surprisingly high percentage of manual wheelchair users were able to traverse fairly steep ramps (75% at 1:8), and to did so without expending energy at risky levels. This suggests that when other variables that could impact ramp use (e.g. side slope, lengthwise slope, surface texture and environmental conditions) are controlled, the 1:12 maximum slope currently allowed by access codes seems to be acceptable for a 30 foot distance and that ramps steeper than 1:12 might be acceptable if there were shorter distances between level landings.

REFERENCES

Canale, I., Felici, F., Marchetti, M. and Ricci, B. (1991). Ramp length/grade prescriptions for wheelchair dependent individuals. Paraplegia, 29, 479-485.

Elmer, C. D. (1957). A study to determine the specifications of wheelchair ramps. Unpublished masters thesis. University of Iowa.

Steinfeld, E., Schroeder, S. and Bishop, M. (1979). Accessible Buildings for People with Walking and Reaching Limitations. Washington, DC: US Dept of Housing and Urban Development, USGPO.

ACKNOWLEDGMENTS

Funding for this study was provided by the U.S. Archi- tectural and Transportation Barriers Compliance Board.

Jon A. Sanford Center for Universal Design North Carolina State University 924 S. Candler St. Decatur, GA 30030