David R. Smith

September 25, 2002

You may recall meeting with a group of persons from the segmental paving industry a while ago concerning proposed research on the interaction of wheelchairs and pavement. The results of that research are attached.

Please enter the attached letter [below] and research report  [PDF version]  (23 pages) into the public comment on the draft ADAAG for the public right of way.

Please direct questions about the letter or report to my attention.

Thank you for your time and efforts.

Sincerely,
David R. Smith, Technical Director
Interlocking Concrete Pavement Institute

---

September 25, 2002

 

Mr. Thurman M. Davis, Sr., Chair
Members of the U.S. Architectural and Transportation
            Barriers Compliance Board
1331 F Street NW Suite 1000
Washington, DC 20004-1111

Re: Public Comment on The Americans with Disabilities Act (ADA) Accessibility Guidelines for Buildings and Facilities; Architectural Barriers Act (ABA) Accessibility Guidelines; Public Right of Way

 

Dear Mr. Thurman and Board Members:

Thank you for the opportunity to comment on the subject accessibility design guidelines for the public right-of-way. The following is from the Interlocking Concrete Pavement Institute (ICPI), The Brick Industry Association (BIA), and the National Concrete Masonry Association (NCMA). These organizations represent manufacturers of segmental pavers made from concrete and clay. These organizations represent industries that produced approximately 450 million square feet of segmental paving in 2001.

We are asking the Access Board to accept concrete and clay segmental paving systems as suitable surfaces for the proposed 48 in. wide pedestrian access route. The rationale for this follows.

Background

On January 10, 2001, the Public Rights-of-Way Access Advisory Committee (PROWAAC) commissioned by the Access Board released a report entitled, Building a True Community. The Committee’s report proposed a 60 in. wide pedestrian access route having within it a 48 in. wide “reduced vibration zone.” The intent of this zone is to eliminate irregular surface features for users of wheel mobility devices, and wheelchairs in particular. Page 45 of the PROWAAC report advises that surfaces consisting of “individual paving units, bricks or other textured materials” were identified as examples of undesirable surfaces in the pedestrian access route because of the vibration they cause to users of wheeled mobility aids.

The report proposed (p. 45) making the pedestrian access route “as free of jointed surfaces and as visually uniform as possible.” It further advised on the need “to eliminate, to the greatest extent possible, surfaces that cause the front end of a wheelchair to vibrate or bounce as one travels across the surface.” It further cited an existing FHWA publication, Designing Sidewalks and Trails for Access, as support. With little supporting data, the FHWA guidebook identified segmental paving as (1) increasing the amount of work for wheelchair users, (2) creating a bumpy ride for wheelchair users, and (3) possibly creating tripping hazards due to differential settlement. For these reasons brick and cobblestone were not recommended by the FHWA for sidewalk and trail design.

Page 39 of the PROWAAC report identified a need for research on the measurement of the rolling vibration of pedestrian surfaces. A need was expressed for investigations into surface roughness, surface wavelength (vibration), and wheelchair features. The need for research is given further discussion in the commentary section of the subject proposed ADAAG for the public right-of-way.

On July 17, 2002, the Federal Register announced the release of the draft ADAAG for the public right-of-way for public review. Concerning Section 1103 Pedestrian Access Route, we applaud the Access Board for not taking action on determination of approved surfaces for the proposed 48 in. wide route (reduced from 60 in.). We would like to see the same acceptance in the reduced vibration zone, should that appear in the final guidelines.

The commentary in the draft on Surfaces 1103.6 notes that research was recommended on the relationships between surface roughness and wheeled mobility aids, as well as on the development of measurement protocols. In light of the need for research, we were pleased to see that no requirement for surface smoothness was included in the proposed ADAAG for the public right-of-way. In response to this need, the ICPI, BIA, and NCMA have taken a leadership role by jointly funding research on surface smoothness of pavements. The results can assist the Access Board in developing guidelines for smoothness and these are presented below. We were also pleased to read the commentary on Changes in Level (1103.8) that did not “rule out the use of bricks of other small pavers that are installed in a manner that provides a relatively flush surface and that are properly maintained.”

Research

The need for a better understanding of interaction between wheelchairs and segmental paving challenged us to conduct research. The ICPI, BIA and NCMA engaged the University of Pittsburgh, Department of Rehabilitation Science & Technology to investigate the interaction of segmental pavement surfaces with manual and electric powered wheelchairs. Professor Rory A. Cooper, Ph.D. was the principal investigator. He is considered the leader in wheelchair design, testing, and the development of that industry’s standards. You may wish to review his curriculum vitae on the web at  http://www.shrs.pitt.edu/temp/rst/about/faculty/cooper.html. A copy of his research report is attached to this public comment in pdf format.

We would like to summarize the report and provide some recommendations. In March 2002, six test pavements were built outdoors adjacent to Professor Cooper’s facility, the Human Engineering Research Laboratory at the Veterans Administration Hospital in Pittsburgh. Each test pavement was 4 ft. wide by 25 ft. in length. They included a poured concrete sidewalk having a broom finish with tooled joints every 4 ft. Three adjacent areas were paved with 4 in. wide by 8 in. long rectangular concrete pavers placed in a 90 degree herringbone pattern. The units in each of these three areas differed only in chamfer sizes specifically consisting of 8 mm wide, 2 mm wide, and no chamfers. Two additional test pavements consisted of 4 in. by 8 in. clay pavers set in a 45 degree herringbone pattern. One of these areas had units with a 4 mm chamfer and the other had no chamfers. With the exception of the concrete paver with an 8 mm chamfer, these concrete and clay pavers were selected because they represent the majority of paving units in the public right of way.

The chamfer is the beveled surface around the top edge of a paver. Its dimension is a critical factor in surface vibration. Its dimension is measured from the place where it begins to angle away from the top surface to the outside edge of the paver. (See the figure below.) It is molded into the paver for the purpose of reducing chipping during transit and installation, as well as facilitating removal of surface runoff. Chamfers are also beneficial for increasing slip and skid resistance.

The design of the experiment included an instrumented manual wheelchair traveling at 1 m/s (typical walking speed) and an instrumented powered wheelchair traveling at 1 m/sec and 2 m/s (cruise speed). Instrumentation consisted of accelerometers at the footrest and on the seat of each wheelchair.

There are many wheelchairs on the market and those selected for use in this research were considered typical to those in service. Ten unimpaired persons 23 to 55 in age, volunteered as test subjects. Each surface was traversed three times while taking measurements, making a total of 540 runs across the pavements. Using impaired persons was not possible due to legal limitations.

The purpose of the experiment: (1) Measure the accelerations (vibration) including peak accelerations; (2) Through extrapolation of the data, compare the accelerations to the vibration exposure limits found in ISO 2631, Evaluation of Human Exposure to Whole-Body Vibration. This standard sets limits to the number or minutes and frequencies of vibration (hertz) to which the human body can be exposed. (3) Test for any significant difference in the work required to traverse each surface with a manual wheelchair. This was done with the same device specified in ASTM F 1951, Standard Specification for Determination of Accessibility of Surface Systems Under and Around Playground Equipment. The tests were done during the summer of 2002.

Research Results

The results found that there was no difference in the amount of work required to traverse any of the surfaces. For the manual wheelchair moving at 1m/sec, peak accelerations were found to be lower than those from the poured concrete surface, except for the concrete pavers with 8 mm wide chamfers. A similar pattern emerged in that overall vibration was lower among the paver surfaces than the poured concrete surface, except the paver with 8 mm chamfers which had mixed results. 

For the electric powered wheelchair moving at 1 m/s, the poured concrete surface generated higher peak accelerations compared to the concrete and clay pavers with no chamfer and the clay paver with a 4 mm chamfer. Again, with the exception of the pavers having 8 mm wide chamfers, all other segmental pavements produced lower vibrations than the poured concrete surface. The poured surface and the concrete pavers with an 8 mm chamfer generated similar vibrations.  

For the powered wheelchair at 2 m/s (cruise speed), the results were similar to moving at 1 m/s. The poured concrete surface generated higher peak accelerations compared to the concrete and clay pavers with no chamfers, and the clay paver with a 4 mm chamfer. Similar to the 1 m/s velocity, at 2 m/s, all pavers except those with 8 mm wide chamfers produced lower vibrations than the poured concrete surface. The poured surface and the concrete pavers with an 8 mm chamfer generated similar vibrations.

Comparison to ISO 2631

ISO 2631 specifies vibration exposure limits to human body for 8 hours. First, the standard doesn’t account for recovery periods. It assumes that exposure is for a continuous 8 hours. This standard must be compared to the behavior of wheelchair operation that is quite different. There are likely to be very few wheelchair users that travel for 8 hours with no stopping.

In support of this observation, Dr. Cooper references behavioral studies that show that users of electric powered wheelchairs move in them a total of about 3 hours a day. Those that use manual powered wheelchairs generally are moving between 2 and 3 hours per day. Furthermore, electric powered wheelchairs are more prevalent for outside use on the pedestrian access route. Table 3 excerpted from the report demonstrates that the surfaces tested fit within these time frames for normal daily use of manual and powered wheelchairs. All surfaces meet the typical daily exposures with the exception of the pavers with 8 mm wide chamfers.

Table 3. Comparison to ISO 2631 exposure limits.

 

Recommendations

The report recommends that all pavers except that with an 8 mm chamfer are acceptable for use in the pedestrian access route. The report further states that the pavers with an 8 mm chamfer gave mixed results and may need further study. We agree with the findings and report. We would like to underscore the point that pavers with 8 mm wide chamfer is larger than most chamfered pavers and was used for the purpose of providing an extreme gap between pavers. The typical chamfer dimension ranges between 4 and 6 mm. Therefore, most chamfered pavers in use would generate lower vibrations than evidenced in the report, and a higher capacity for exposure time when evaluated according to ISO 2361.

With the support of Dr. Cooper’s report, we have demonstrated that the most common types of segmental paving are acceptable for pedestrian access route and for the proposed reduced vibrations zone. Clearly, the chamfer width is a key factor in keeping vibrations near or below that of typical jointed, poured concrete sidewalk surfaces. The results indicate that the number of joints in a sidewalk have little impact on smoothness and vibration. Rather, joint widths have a substantial influence. Other factors affect smoothness such as lippage (vertical displacement), the quality of the construction materials and procedures, as well as maintenance and repair of the surface during its use.

Dr. Cooper’s report has some positive implications for the future of ADAAG for the public right-of-way. First, he uses established research methods and analytical tools that can be applied to other surfaces and wheelchairs. Second, these methods could be a basis for establishing surfaces acceptable for use in the pedestrian access zone and proposed reduced vibration zone. Third, these methods could be the basis for developing a portable, inexpensive measurement device for making such assessments. Dr. Cooper has expressed an interest in developing a prototypical device. Such research and development would advance the objective identifying measurable technical specifications.

Our final and strongest recommendation is to maintain Section 1103 as drafted. We would request that Dr. Cooper’s research report be referenced in notes or commentary that might accompany the final guidelines. Finally, we would be interested in reviewing the possibility of participating in research aimed at developing measurement methods and specifications for surface smoothness.

Thank you for your time and consideration.

Sincerely,

Charles A. McGrath. CAE  
Executive Director 
Interlocking Concrete
Pavement Institute                                                                                                                                             

Richard Jennison
President
Brick Industry Association 

Mark Hogan, P.E. 
President
National Concrete
Masonry Association

Attachment - report  [PDF version]

 

cc:  Jerry Markesino, City of Portland, OR, Office of Transportation, PROWAAC Chair 

Don Brandon, State of Alaska, PROWAAC Subcommittee Chair on Sidewalks

Paul Church, Disability Rights Education Defense Fund, PROWAAC Subcommittee on Sidewalks, Surfaces Working Group