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Assistive Technology: The Official Journal of RESNA Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/uaty20

Pedestrian Pathway Characteristics and Their Implications on Wheelchair Users Jonathan Pearlman PhD BS

a b

, Rory Cooper PhD

a b

, Jonathan Duvall BS

a b

& Ryan Livingston

a b

a

Human Engineering Research Laboratories, VA Rehabilitation Research & Development Center of Excellence for Wheelchairs and Associated Rehabilitation Engineering , VA Pittsburgh Healthcare System , Pittsburgh , Pennsylvania b

Departments of Rehabilitation Science & Technology, Physical Medicine & Rehabilitation, and Bioengineering , University of Pittsburgh , Pittsburgh , Pennsylvania Accepted author version posted online: 04 Mar 2013.Published online: 14 Oct 2013.

To cite this article: Jonathan Pearlman PhD , Rory Cooper PhD , Jonathan Duvall BS & Ryan Livingston BS (2013) Pedestrian Pathway Characteristics and Their Implications on Wheelchair Users, Assistive Technology: The Official Journal of RESNA, 25:4, 230-239, DOI: 10.1080/10400435.2013.778915 To link to this article: http://dx.doi.org/10.1080/10400435.2013.778915

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Assistive Technology® (2013) 25, 230–239 Copyright © 2013 RESNA ISSN: 1040-0435 print / 1949-3614 online DOI: 10.1080/10400435.2013.778915

Pedestrian Pathway Characteristics and Their Implications on Wheelchair Users JONATHAN PEARLMAN, PhD1,2∗ , RORY COOPER, PhD1,2, JONATHAN DUVALL, BS1,2, and RYAN LIVINGSTON, BS1,2

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1

Human Engineering Research Laboratories, VA Rehabilitation Research & Development Center of Excellence for Wheelchairs and Associated Rehabilitation Engineering, VA Pittsburgh Healthcare System, Pittsburgh, Pennsylvania 2 Departments of Rehabilitation Science & Technology, Physical Medicine & Rehabilitation, and Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania

Individuals who use wheelchairs (WCs) frequently navigate over pathways with obstacles (e.g., bumps or curb descents) or terrain that is extremely rough. Surface characteristics such as roughness can have an effect on comfort and variables associated with bodily injury. Understanding these relationships can be helpful to ensure safe and comfortable access to all public and private pathways. This article reviews existing research related to the topics of surface roughness effects on WC user’s bodies, surface roughness measurement techniques, and design guidelines and exposure limits that attempt to ensure pathways are safe and passable. These findings are discussed along with opportunities to improve them. Using a broad literature search, it was found that several measurement and analysis techniques exist to characterize surface roughness related to automobile roadways, but they have not been systematically applied to WC use over pedestrian pathways. The roughness measurement approach that appears most relevant and adaptable for sidewalks are rolling profilers. Commercially available devices could be recalibrated or adapted to measure pedestrian pathways. IRI and ride-quality analysis techniques appear most relevant and could also be adapted. Any analysis technique that uses profiles of surfaces should focus on frequencies and wavelengths that are most applicable to WC riders. Keywords: accessible, pathway, roughness, whole-body vibrations

Introduction The Architectural Barriers Act of 1968 (ABA) ensures that buildings that are designed, built, or altered by federal funding or leased by federal agencies are accessible to the public. The Americans with Disabilities Act of 1990 (ADA) greatly expands the scope and details of the ABA. The ADA states that “physical or mental disabilities in no way diminish a person’s right to fully participate in all aspects of society” (ADA § 12101(a)(1)). It is a purpose of the ADA “to provide a clear and comprehensive national mandate for the elimination of discrimination against individuals with disabilities and to provide clear, strong, consistent, enforceable standards addressing discrimination against individuals with disabilities” (ADA § 12101(b)(1)). Title V of the ADA mandated that the Architectural and Transportation Barriers Compliance Board (Access Board) setup minimum guidelines “to ensure that buildings, facilities, rail passenger cars, and vehicles are accessible, in terms of architecture and design, transportation, and communication, to individuals with disabilities” (ADA § 12204(b)).

∗

Address correspondence to: Jonathan Pearlman, PhD, Human Engineering Research Laboratories, 6425 Penn Ave., Suite 400, VA Pittsburgh Healthcare System, Pittsburgh, PA 15206. Email: [email protected]

People with disabilities can participate in the community and have very active lifestyles. A study has shown that people in Pittsburgh, PA who use power wheelchairs (WCs) as their primary mode of transportation will travel 1.6 km on a normal day (Cooper et al. 2002). However, in an active environment, such as at the National Veterans Wheelchair Games (NVWG), they can travel up to almost 8 km per day (Cooper et al., 2002). A similar study of manual WC users revealed that on typical days they travel 2.0 km, and in an active setting, such as at the NVWG, they will travel an average of 6.5 km per day; one subject in this study traveled 19.4 km in one day (Tolerico, 2006). A factor that influences this activity level is the degree to which the WC rider is comfortable and safe during these activities. One of the most widely used measures of comfort and safety is to determine the level of whole-body vibrations (WBV) exposed to the rider. There is a wide body of occupational hazards research that has demonstrated a correlation from WBV exposure to discomfort and injury to nearly all of the body’s organs. Research suggests that exposure to shock and vibration may be linked to many symptoms such as muscle fatigue (Zimmerman, Cook, & Goel, 1993), back injury (Pope & Hansson, 1992; Pope, Wilder, & Magnusson, 1999), neck pain (Boninger et al., 2003), and disc degeneration. Literature suggests that the seated posture, which occurs during WC use, is a compromising position for the spine and many associated body tissues. Daily shock and vibration experienced during WC riding can also increase an individual’s rate of fatigue

Pedestrian Pathway Characteristics

231 Table 1. ADAAG accessible route guidelines. Parameter

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Clear Width Openings Obstacle Height 0.25 inches 0.25–0.5 inches Ramps Max Slope 1:12–1:16 1:16–1:20 Cross Slope

Fig. 1. ISO Standard 2631. The health guidance zone is between the dashed lines. © ISO. This material is reproduced from ISO/IEC 27002:2005 with permission of the American National Standards Institute (ANSI) on behalf of the International Organization for Standardization (ISO). No part of this material may be copied or reproduced in any form, electronic retrieval system or otherwise or made available on the Internet, a public network, by satellite or otherwise without the prior written consent of ANSI. Copies of this standard may be purchased from ANSI, 25 West 43rd Street, New York, NY 10036, (212) 642-4900, http://webstore.ansi.org .

(VanSickle, Cooper, Boninger, & DiGiovine, 2001) and limit their functional activity and community participation. Because of these harmful effects, it is critical to understand and attempt to reduce the amount of WBVs that are transmitted when navigating over rough terrains. (Cooper et al., 2004; Requejo, Maneekobkunwong, McNitt-Gray, Adkins, & Waters, 2009) The ISO 2631-1 standard for evaluation of human exposure to WBV is the most accepted standard for vehicle vibration studies and establishes limits for safety, fatigue, and comfort called the exposure caution zone. The exposure caution zone (Figure 1) is based on the time of exposure and weighted magnitude of acceleration and reflects the maximum allowable limit for human safety. Furthermore, according to the ISO 2631-1, an RMS value of 1.15 m/s2 over a 4–8 hour period is the maximum allowable vibration value. However, exposure of vibration levels within the caution zone may still result in elevated risk of health impairment (ISO, 1997) if they occur repeatedly over a long period of time (e.g., several years). The Access Board has established ADA Accessibility Guidelines (ADAAG) for buildings and facilities that give specific instructions and limitations about what is considered accessible. However, the only guidelines related to floor or ground surfaces are that they “shall be stable, firm, and slip resistant” (ADA, 36 CFR Appendix D to Part 1191, § 302.1, 2010). Unfortunately, these restrictions can be interpreted differently, and do not directly address the issue of surface roughness. Typical ADA accessible pathways are made of asphalt, pavement, or concrete; however, other pathway materials–such as packed, crushed stone, gravel fines compacted with a roller, packed soil, and various natural materials bonded with synthetic materials–can provide the required degree of stability and firmness (Regulatory Negotiation Committee, 1999). The current ADAAG guidelines (Table 1) provide a description of the suggested width and slope,

Requirement Minimum 36 inches Maximum 0.5 inches No slope required Maximum 1:2 slope Maximum 30 inches high, 30 feet long Maximum 30 inches high, 40 feet long Maximum 1:50

but do not provide guidance on pathway roughness except that obstacles should be no more than 0.5 inches high. The frequency (obstacles per unit length), profile, and orientations of safe and passable obstacles are not prescribed (Americans with Disabilities Act Accessibility Guidelines, 2010). The absence of roughness guidelines is an unfortunate limitation to the ADAAG, as there are many stakeholders involved in the development processes and construction of public walkways (i.e., city planners, community councils, architects, and contractors) each of which are not likely to understand the implications of terrain characteristics on the health, comfort, and safety of WC riders. It is important to develop a guideline to help the stakeholders design, select, test, and monitor the performance of these surfaces. It is also important that the guidelines not be restrictive such that they discourage design innovation; rather the guidelines should be versatile and applicable to surfaces of all types, both existing and those which will be developed in the future. As a first step in the process of developing a roughness design guideline, it is necessary to interpret relevant literature about the topic within and outside of research focused on WC riders. The research will provide a perspective on the types of measurements and instrumentation that have been used to establish design guidelines in related fields, and also a better understanding of the health implications of vibration exposure on seated individuals. Therefore, we undertook this literature review to understand the current state of research related to surface roughness measurement and analysis, as well as the implications of surface roughness on the health and safety of humans. The long-term goals of this research are to be able to develop measurement tools and a standard of surface roughness to help ensure public right-of-ways are safe and comfortable for WC riders.

Methodology This article encompasses two topics. The first is a review of the literature focusing on the effects of surface roughness on the health and safety of WC riders. The second topic is to explore ways to measure, design, and monitor the quality of pathway surfaces for WC users. Therefore two separate searches were conducted. A literature review was completed using searches on PubMed and Google Scholar in October of 2010, and more recently in November of 2011 to identify any new articles. For the search on WC vibrations, both databases were searched for titles that had the word wheelchair and any of the following: vibration, shock, surface, roughness, firmness, sidewalk, or pathway. The second search was conducted by searching titles

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for the word roughness and any of the following: road, roadway, measurement, profile, or profiling. This second search was only conducted on Google Scholar and was limited to the fields of engineering, computer science, and mathematics. We performed a systematic review of the relevant literature. Relevance was determined first by reviewing abstracts, and then reviewing entire articles. First, abstracts of all of the papers identified through the keyword searches were compiled into a single document, and each was reviewed by at least two of the authors of this article. If at least one reviewer believed the abstract suggested the manuscript was relevant to the topic, the entire manuscript was then reviewed by at least two of the authors. Only manuscripts that two reviewers deemed irrelevant were then discarded, and the remaining manuscripts were included in this review article.

surfaces added in the last year. Wolf et al. compared poured concrete (control) to different types of brick sidewalks. They varied in composition (concrete and clay), spacing (bevel size and no bevel), and degree of herringbone placement (45 degrees and 90 degrees), as shown in Table 2. Sidewalks were installed by an Interlocking Concrete Pavement Institute (ICPI) certified contractor. Ten nondisabled subjects were recruited over the 3-year period. Accelerations were recorded on the seat and footrest of the chair as the subjects drove over the surfaces. Wolf et al. concluded that for manual WCs, the 90-degree surfaces with 0- and 2-mm bevels resulted in significantly lower WBV than the standard poured concrete surface. For power WCs, the 90-degree surface with no bevel resulted in significantly less WBV at the seat and the 90-degree surfaces with 0-, 2-, and 4-mm bevels resulted in significantly less WBV at the footrest than the poured concrete surface. The results also showed that the 90-degree

Results The database search for WC vibrations resulted in 217 articles on PubMed and 117 on Google Scholar. After scanning the titles for relevancy, 21 articles from PubMed and 32 articles from Google Scholar remained, with 5 articles appearing in both. The abstracts and full articles were reviewed to select which articles to include. The database search for roughness measurements resulted in 398 titles. These articles were scanned for relevancy and organized. As will be discussed later, it was found that there are several approaches to the measurement and analysis of surface roughness. Rather than referencing many articles to explain these approaches, we identified a few sources that summarized the information. Table 3 shows the final manuscripts that are summarized and referenced in the next sections. WC Vibrations Of the articles found on WC vibrations, several are relevant to surface roughness and the different effects of varying surfaces for WC users. A focus group study that consisted of manual and power WC users was conducted to determine the problems users experience with their WCs. The study revealed that users complained about the rough ride on uneven surfaces like bricks and uneven/broken sidewalks (Meruani, 2006). A study done by Wolf, Cooper, Pearlman, Fitzgerald, and Kelleher (2007) looked at the effects of roughness of nine different sidewalk surfaces; six studied over three years and three

Table 3. Summary of included manuscripts found from literature reviews. Reference 1 2 3 4 5 6

Topic

7

Axelson & Chesney (1999) Latif (2009) Chesney & Axelson (1996) Cooper et al. (2004) Gillespie (1992) Yamanaka & Namerikawa (2006) Ishida et al. (2006)

8

Loizos & Plati (2008)

9

Maeda et al. (2003)

10 11

Meruani (2006) Sayers & Karamihas (1998)

12

14

Shafizadeh & Mannering (2002) University of Washington (2005) Wei et al. (2004)

15

Wolf et al. (2007)

13

Surface firmness Profile analysis technique Surface Firmness Wheelchair vibrations Profile analysis technique Surface Roughness Analysis Technique Surface measurement and evaluation Surface analysis technique Survey and vibration correlation Wheelchair vibrations Surface evaluations and analysis Road rating Road rating Surface analysis technique Wheelchair vibrations

Table 2. Specifications of surfaces tested. Dimension (mm) Surface 1 2 3 4 5 6 7 8 9

Name

Edge Detail

Composition

Length

Width

Height

Installed Pattern

Poured Concrete Holland Paver Holland Paver Holland Paver Whitacre-Greer Pathway Paver Holland Paver Holland Paver Holland Paver

— Square (no bevel) 2 mm bevel 8 mm bevel 4 mm bevel Square (no bevel) 6 mm bevel 6 mm bevel 4 mm bevel

Concrete Concrete Concrete Concrete Clay Clay Concrete Concrete Concrete

— 198 198 198 204 204 198 198 198

— 98 98 98 102 102 98 98 98

— 60 80 60 57 57 60 60 60

Smooth 90◦ 90◦ 90◦ 45◦ 45◦ 90◦ 45◦ 90◦

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Pedestrian Pathway Characteristics surface with an 8-mm bevel had the highest WBV while the 90-degree surface with no bevel resulted in the lowest WBV. The fact that the poured concrete surface resulted in significantly higher vibrations than some brick surfaces was most likely caused by the large gaps between the slabs of concrete (Wolf et al. 2007). Another study conducted on six of the same surfaces (poured concrete; 90-degree surface with 0-, 2-, and 8-mm bevels; 45-degree surface with 0- and 4-mm bevels) showed that for power WCs traveling at a speed of 1 m/s, the ISO 2631 limit for an 8-hour exposure to vibrations was exceeded by the 90degree surface with 8-mm bevel and 45-degree surface 4-mm bevel. At a speed of 2 m/s the exposure limit would be exceeded in less than 3 hours of continuous driving on all surfaces (Cooper et al., 2004). While WC users do not typically drive continuously for 3 hours, they do travel more than 8 hours a day on average and experience some amount of vibrations during all movement (Tolerico, 2006). Surface firmness (materials such as sand and wood) has been investigated by asking WC users how difficult it is to traverse over different surfaces using a Likert scale. Difficulty level was correlated with the following conditions: (a) a decrease in traveling speed, (b) an increase in heart rate, and (c) increase in total energy consumption. Compared to other outside surfaces studied, dirt, chipped brush, engineered wood fiber, and sand were the most demanding for the WC users to traverse. Alternatively, the most firm and stable surfaces in dry conditions were asphalt, unpaved road mix, path fines (a type of decomposed granite), path fines with stabilizer, and native soil (Axelson & Chesney, 1999). Axelson and Chesney’s study (1999) acknowledged the subjectivity of the survey data as a limitation and addressed it by developing objective measurements of surface firmness. The project used the Wheelchair Work Measurements Method and a rotational penetrometer to determine the firmness. The work measurement method recorded work-per-meter values for both straight and turning propulsions on all test surfaces in both dry and wet conditions. The rotational penetrometer (Figure 2) is a portable device that gives accurate measures of firmness and stability on surfaces, and is widely applicable to field tests. Firmness was measured by applying a force using a calibrated spring and measuring the depth of penetration of the indenter. Stability was measured by applying a force with a calibrated spring and rotating the spring loaded indenter back and forth 90 degrees four times and measuring the final depth of penetration into the surface (Axelson & Chesney, 1999). Another study used the SMARTwheel (Out-front, Meza, AZ) to objectively measure the firmness of a surface through push rim forces. The force- and torque-sensing wheel determined the beginning and ending phase of each propulsion cycle using a data analysis program in MatLab to properly identify torque required. The end result was a work-per-meter measure of the work performed. This method provides the sensitivity and accuracy to measure < 1% in grade and differences in surfacing materials. It should be noted that this measurement method has been incorporated into American Society for Testing and Materials (ASTM) F1951 to determine the accessibility of playground surfaces. The forces required to roll the WC and turn the WC must be less than the force required to roll up and turn on a 7.1% grade ramp (Chesney & Axelson, 1996).

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Fig. 2. Penetrometer (Axelson & Chesney, 1999). © PAX Press, a division of Beneficial Designs, Inc., June 21, 1999, Accessible Exterior Surface Technical Article.

Mobility speed is also an important factor in considering the effects of surface roughness on the whole body. Meruani (2006) conducted a study to compare two types of wheels on multiple surfaces (i.e., smooth and rough concrete, grass, gravel, and sand) and analyzed many outcome variables, such as durability, impact of vibration and surface roughness, obstacles, and comfort levels. The results indicated that only low speed mobility on smooth concrete surfaces using standard tires fell below the ISO caution zone; all other test values fell above the upperboundary set by ISO standards for 4-hour period (root mean square [RMS] = 1.15 m/s2 ). Evidence suggests prolonged exposure at these levels may have detrimental impact on the health effects and comfort on WC users (Meruani, 2006). WC rolling resistance has been another measurement of WC comfort. Ishida et al. (2006) evaluated the unevenness of sidewalks and the association between unevenness and the torque required to propel. Torque was recorded by a torque-sensor attached to a modified WC with a fixed rear axle and logged 1-second intervals on a data logger. The study reported the torque associated with a round trip at 56 different 5-m profiles of sidewalks. Eleven profiles had smooth surfaces and gradients ranging from 0–10%. The other profiles included substantial unevenness. The second part of the study involved subjects propelling themselves across a 5-m test track: one horizontal and flat, and another flat with a 5% gradient. The track was then modified to have varying degrees of unevenness and compared their level of discomfort to the smooth tracks by rating it from -1–6 (0 if it was the same as the horizontal track and 5 if it was the same as the 5% grade track). The results revealed a very strong correlation between surface unevenness and comfort (Figure 3). Not only did the torque data show effects of the uneven traveling paths, but the users also agreed with the difficulty of the tracks. The study helped establish standards for the Standard for Level Differences and Gradients

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Fig. 3. (a) Schematics of test tracks. (b) Table of test track characteristics. (c) Graph of discomfort versus cumulative level difference. From Ishida, T., H. Takemoto, S. Ishida, S. Kameyama, K. Himeno, and S. Kashima. Evaluation of Sidewalk Unevenness Based on Wheelchair Traveling Resistance. In Transportation Research Record: Journal of the Transportation Board, No. 1956, Figure 3(a), p. 72 and Table 1, p. 73. Copyright, National Academy of Sciences, Washington, D.C., 2006. Reproduced with permission of the Transportation Research Board.

on Sidewalks for promoting safety and accessibility (Ishida et al., 2006). The three principle rules being: “(a) sidewalks should have a continuous level surface with an effective width of at least 2 m; (b) sidewalks should have a standard gradient of less than 5% and a standard cross slope of less than 1%; and (c) the standard difference in the level at the boundary between the roadway and the sidewalk should be no more than 2 cm” (Ishida et al., 2006, p. 68). As demonstrated by Ishida et al. (2006), a valuable tool to indirectly measure the effects of surface roughness on the whole body is the use of surveys from the WC users themselves. The relationship between WC users’ awareness and the physical effects caused by the rough terrains has been studied by Maeda, Futatsuka, Yonesaki, and Ikeda (2003). Thirty-three WC users were studied in an attempt to obtain the degree and area of complaints concerning vibration due to the WC ride. Results showed surfaces affected ride comfort with the most common areas affected being the neck, lower back, and buttocks (Maeda

et al., 2003). There are also other indirect measurements that can be taken to look at how bumps, obstacles, and other surface variables affect WC users, such as injuries, energy expenditures, and physiological responses. Surface Measurement Methods There are currently several methods of measuring and recording surface profiles including the rod and level, dipstick, rolling straight-edge, profilograph (Figure 4), rolling profilers, RoadResponse Type Measuring System (RRTMS; Figure 5), and inertial profilers (Figure 6). One of the original methods was the Profilograph, which was adopted in the early 1900s, and can directly measure surface roughness by using an array of wheels on each side to establish a reference plane for measuring deviations (Figure 4). The roughness is measured as the absolute sum of deviations of the center wheel (Gillespie, 1992; Sayers & Karamihas, 1998).

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Fig. 4. Schematic of Profilograph (Sayers & Karamihas, 1998).

Fig. 5. Schematic of RTRRMS (Sayers & Karamihas, 1998).

Fig. 6. Schematic of inertial profiler (Sayers & Karamihas, 1998).

During the 1960s, an automobile-mountable measurement device began a new era of surface roughness measurements, with some advantages and disadvantages. The major advantages of these systems were their low cost and their ability to mount onto any vehicle. These RTRRMS systems recorded cumulative axle displacement over a given distance and thus reported surface roughness as inches/mile. Also known as road meters, two examples of these systems are the Mays Ride Meter and the PCA Meter. (Gillespie, 1992; Sayers, 1998; Figure 5). The disadvantages to using the RTRRMS were the inconsistencies introduced by variations between the different commercialized RTRRMS and also the fact that they were mounted onto different automobiles that may have had different suspension systems. Consequently, measurements from identical surfaces could be different depending on which device and automobile were used. This effect was compounded by the influence of minor differences even within identical vehicles, such as fuel level, number of passengers, or tire pressure. With these variabilities, developing a consistent and reliable database of road roughness measures and related thresholds was impossible. The need for standardized and consistent measures was necessary throughout the world. This led to the development of an effort organized and conducted by the World Bank in Brazil in 1982, known as the International Road Roughness Experiment.

235 One goal of the experiment was to establish a correlation and calibration standard for roughness measurements. In processing the data, it became clear that nearly all roughness measuring instruments in use throughout the world were capable of producing measures on the same scale, if that scale was suitably selected. A number of methods were tested, and the “in/mi” calibration reference from NCHRP Report 228 was found to be the most suitable for defining a universal scale (Gillespie, 1992; Sayers & Karamihas, 1998). Another method of measuring surface profiles is with an inertial profiler (Figure 6). An inertial profiler uses an accelerometer and a non-contacting sensor, such as a laser transducer, to measure height. Data processing algorithms convert vertical acceleration measured by the accelerometer to an inertial reference that defines the instant height of the accelerometer in the host vehicle. The height of the reference from the ground is measured by the sensor and subtracted from the reference. The distance traveled is usually measured by wheel rotations or a speedometer. These profilers are convenient because they can be attached to any vehicle. However, because they use acceleration measurements, they are inaccurate at low speeds. Most roadway inertial profilers cannot measure accurately at speeds less than 15 km/hr (Sayers & Karamihas, 1998). The Present Serviceability Index (PSI) is another method of measuring surface roughness and performance of pavement. It is the first and most commonly used method for relative objective measures of surface condition with the public’s perception of serviceability. However, the primary use of PSI is to evaluate the ability of the pavement to serve its users by providing safe and smooth driving surfaces. Between 1958 and 1960, the American Association of State Highway Officials conducted a study of pavement performance on surfaces in Illinois, Minnesota, and Indiana (University of Washington, 2005). A panel of raters evaluated roadway surfaces by riding in a car over the pavement and filling out a Present Serviceability Rating (PSR) form (Figure 7). While the PSR measurements were being conducted by the panelists, other objective measurements (i.e., total crack length, slope variance, and rutting depth) were being taken on the same roads. The PSI equations (Equation 1) were derived to be able to use the objective measurements of the road to predict the panel’s rating. These equations allowed objective measurements taken from a stretch of highway to predict the rider perception of that roadway and thus be a way to determine whether the pavement is acceptable or needs to be replaced. The PSI equations produce a scale of 0–5; 5 indicates an excellent ride condition while 0 refers to a very poor ride quality. Manual observation is still considered possibly the strongest and most accurate evaluation of a road surface because of their attention to detail; however, it requires a substantial amount of human hours and associated cost (Latif, 2009; Sayers & Karamihas, 1998; University of Washington, 2005) √ PSI = 5.03 − 1.91 LOG (1 + sv) − 0.01 C1 + Pa − 1.38(Rd)2 (Equation 1) SV = slope variance; Cl = crack length; Pa = patching area; Rd = rutting depth This equation applies for flexible pavement only; other surfaces have different equations

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Fig. 7. PSR evaluation form (Sayers & Karamihas, 1998). Fig. 9. IRI Scale (Sayers & Karamihas, 1998).

Fig. 8. Quarter-car picture and variables (Loizos & Plati, 2008).

Analysis Techniques Several approaches have been developed to process the surface roughness measurements into meaningful indices. These indices include moving average, Ride Number (RN), International Roughness Index (IRI), and Power Spectral Density (PSD). The gold standard for designing and evaluating roadway roughness is the IRI, which was developed by the International Road Roughness Experiment (IRRE) and establishes equivalence between several methods of roughness measurements. The IRI also has an ASTM measurement protocol for consistent measurements. The IRI is the cumulative sum of displacement of the upper mass (Ms) of a standardized “quarter-car” model when it is simulated to travel over a road profile [Z(x)] which was either measured, or generated for the purposes of designing a new roadway. The characteristics of the quarter-car model are shown in Figure 8 (Loizos & Plati, 2008; Sayers & Karamihas, 1998). The strength of the IRI is its stability and portability. Although the “in/mi” measure from RTRRMS has been popular since the 1940s, as discussed earlier, values varied from one vehicle over time or from different vehicles on the same road. Since the IRI model is defined by its mathematical quarter-car model, it is not affected by the measurement procedure or the characteristics of the vehicle that was utilized in collecting the profile measures. Another important factor concerning the IRI is that it was designed to focus on road serviceability. Serviceability is a criterion measure for highway surfaces based on surface roughness, which is then used as a determinant need for rehabilitation of highway surfaces (Loizos & Plati, 2008; Shafizadeh, Mannering, & Pierce, 2002; Figure 9). A study done in Japan (Yamanaka & Namerikawa, 2006) addressed the usability of IRI on sidewalks used by WCs.

The study had 10 subjects ride in a manual WC over 19 different surfaces. The subjects were then asked to rate the smoothness of the ride and if they felt shaking. Vibration measurements were also recorded during the trials using speedometers attached to a caster wheel of the chair. Profile measurements were taken using a Profilograph that could measure displacement on a 10-mm interval. The results showed that there was a strong relationship between user assessment and vibration data. However, the relationship between the IRI and user assessment was not significant. The researchers concluded that this was probably due to the fact that the front tires of the WC would produce vibrations while running over small cracks and bumps that the Profilograph, with a 10-mm interval, could miss. Therefore the person would feel the bump, but the Profilograph would not record it. Although the IRI is accepted as a measure of serviceability in numerous countries, research has indicated that IRI may be limited in predicting serviceability because it is a broad measure of roughness and filters out potentially informative data from small areas of the roadway. Another analysis technique widely used to evaluate roughness is a PSD analysis of the road profiles. The PSD provides a concise description of road roughness measured in frequencies and accompanying amplitudes. This is accomplished by describing the distribution of the pavement profile variance as a function of wavelength. The height (y) of the surface profile represents pavement roughness and is a function of spatial distance (x) along the pavement. To generate a PSD, a Fourier transform of the data is performed and scaled to show how the variance of the profile is spread over different frequencies. PSD analysis is valuable because it helps identify the source of the roughness. Short wavelengths (less than 3 m) are a result of irregularities of the top pavement layers while long wavelengths (10 m or longer) are caused by irregularities found in lower pavement layers (Loizos & Plati, 2008). PSD can also be evaluated in terms of roughness by plotting the PSD of elevation, PSD of slope, or vertical acceleration versus wavelength. The most commonly used are PSD of slope plots because they allow a direct view of the variance within a slope throughout a given distance of the pavement. Slope is also a

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more valuable parameter of pavement surface properties when wavelength is known. These plots can be used for the calculation of an index (RMS) of elevation or slope by calculating the area under the curve to evaluate pavement surface conditions. However, because it is dominated by longer wavelengths, RMS values are not a reliable index measure of pavement surface smoothness. Additionally, RMS indices do not consider parameters such as vehicle speed and characteristics in order to be used to evaluate ride quality (Loizos & Plati, 2008). IRI and PSD are of limited value in predicting serviceability on short roadways, as they must have a reasonably long sample size to obtain accurate estimates; they are also not effective at pinpointing local defects. To address these shortcomings, engineers have also analyzed profile data using Wavelet Theory (WT). This theory decomposes a signal into different frequency components and then presents each component with a resolution matched to its scale. It can detect sharp changes in magnitude of the profile as well as addressing the issue of location where irregularities and deformities occur. Therefore, WT is able to identify the locations of surface revealing, depressions, settlement, potholes, surface heaving, and humps—something that only manual labor intensive subjective procedures were previously able to measure accurately. WT detects these problems through local analysis that reveals the aspects that the other signal analysis techniques miss (discontinuities in higher derivatives and breakdown points and trends). WT also addresses the issue of lost time information, which occurs in PSD analysis, by using short-width and longwidth windows at high and low frequencies, respectively. This gives WT an infinite set of possible basis functions and greatly reduced computation time. (Wei, Fwa, & Zhe, 2004)

none are immediately applicable for surfaces that WC users travel on. WC users travel at much lower speeds than the minimum speed needed to use an inertial profiler; a maximum speed of 2.7 m/s for power chairs compared to 22.2 m/s, which is the minimum speed for inertial profilers. WC users also travel much shorter distances between stops—a maximum of 449 m in an active environment and 175 m at home for manual chairs (Cooper et al., 2002; Tolerico, 2006). For these reasons, inertial profilers may not be the best options. Simple profilers, such as a rod and level or a dipstick, may be better options, although they are currently designed to measure relatively long wavelength road features that may be unimportant to WC riders. These devices would need to be recalibrated to become appropriate for WC riders. Because the most harmful vibrations for people occur at their natural frequency (approximately 8 Hz), a profile measurement which focuses more intimately on wavelengths that would cause these vibrations at a normal WC speed and wheel base is recommended (Cooper et al., 2004). Meruani (2006), as well as VanSickle et al. (2001), showed that it might be possible to attach measuring devices such as accelerometers directly to a WC to measure a surface profile. If a manual chair that has effectively no suspension is fitted with accelerometers, it may be possible to record a surface profile directly from the WC. This would also help determine what surface roughness WC users find uncomfortable. As shown by Maeda et al. (2003), self-report surveys have been shown to be accurate and reliable. The ISO standards for WBV should also be used to determine what is safe.

Profile Analysis

Discussion The long-term goal of this research is to be able to develop measurement tools and a meaningful standard of surface roughness to help ensure sidewalk pathways are safe and comfortable for WC riders. There are many ways to measure a roadway surface profile and also many ways to analyze that profile to develop an objective measure of roughness. Profile Measurements

IRI, WT, and PSD analysis methods may still apply for WC pathways. Once the profile of a surface is obtained, the analysis of that data could be done in a variety of ways. Table 5 summarizes the advantages and disadvantages for each analysis technique. The main difference is that, because of a WCs smaller tires and frame, the frequency of roughness that would affect WC users the most would be much smaller than the frequency that would affect roadway users.

Recommendations

Table 4 summarizes the methods of measuring surface roughness and lists advantages and disadvantages of each. Despite the value of these tools in measuring and interpreting roadway roughness,

Research efforts to develop guidelines for pathway roughness should focus on adapting measurement instrumentation and

Table 4. Advantages and disadvantages of measurement devices and techniques. Measure device

Measurement process

Advantage

Disadvantage

Profilometer

Profilograph

Cost effective, fast measures

Response-type road roughness measurement systems (RTRRMS) Dipstick Rod and Level Inertial Profiler

Cumulative axel displacement (Mays Meter, etc.)

Inexpensive, easy to mount on any automobile

Wide variation in response properties, only measures certain wavelengths Inconsistent measurements between devices, times, and speeds

Inclinometer Inclinometer and laser Accelerations and displacements

Simple, very accurate, low cost Simple, Extremely accurate Inexpensive, Can be mounted to any vehicle

Short profiles, takes a long time Takes an extremely long time Requires a certain amount of speed to work

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Pearlman et al.

Table 5. Advantages and disadvantages of analysis techniques. Analysis techniques International Roughness Index (IRI) Power Spectral Density (PSD)

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Wavelet Theory (WT)

Present Serviceability Index (PSI)

Measure device Quarter-car model or (Any Device) Profilometer or other accepted device to measure surface profiles Profilometer or other accepted device to measure surface profiles Qualified panelist manual observation

Advantage

Disadvantage

Internationally recognized, stable, portable, linear Describes types of roughness by using wavelengths and amplitudes Describes overall and localized roughness

Long measures do not allow localized detail Long measures do not allow localized detail

High level of precision and attention to detail

Subjective Measurements, Requires many man-hours to complete

indices currently used for roadway roughness. This will help streamline the process of developing and gaining acceptance for the roughness standards, as standards will be based on science similar to what is currently accepted. To accomplish this, three measurement techniques need be employed to characterize a series of sidewalk surfaces with varied roughnesses. First, accurate profiles need to be collected of these sidewalk surfaces with an accuracy level that is relevant to WC riders (∼1 mm). This would most easily be accomplished by adapting or developing a rolling profiler. The profiles should then be filtered and analyzed in a manner that develops a useful roughness index. Second, subjective comfort measurements (similar to PSR) need to be collected from WC riders after traversing these sidewalk surfaces. Third, WBV measurements need to be collected while the rider is traveling over each surface. Relationships between profile roughness, subjective comfort measurements, and WBV can then be explored to determine the maximum surface roughness that still ensures comfort and safe levels of WBV. Confounding factors also need to be explored to understand their impact on the above relationship. For example, a recent study measured and compared the dynamic stiffness and transmissibility of five different commercially available WC seat cushions. The results showed that different cushions yield significantly different transmissibility of vibrations (Garcia-Mendez, Pearlman, Cooper, & Boninger, 2012). There are many other factors, such as WC type, suspension, wheel diameter, and injury manifestations, that will cause the vibrations and riders comfort level to change. These factors should be recorded. Additionally, it is unknown how surface characteristics at short (Wolf et al., 2007) and longer (Ishida et al., 2006) wavelengths interact to influence comfort. As found in the Wolf et al. (2007) study, poured concrete surfacing can create significantly higher vibrations for WC users than brick paver surfaces. This potentially indicates a benefit of a properly laid brick paver surfaces that can have lower vibration than the typical concrete panels that have large gaps or large transition heights between them. This leads us to believe that the type of surface may not be as important as how the surface was laid and how it maintains its form over time. Addressing these research questions will likely involve both community- and laboratory-based research studies. Communitybased studies should focus on gathering pathway profiles, WBV,

N/A

as well as some feedback from the WC riders about when they feel discomfort. Laboratory-based trials should focus on having WC riders travel across surfaces of known profiles and report subjective comfort. These laboratory-based trials could involve developing a single surface whose roughness can be adjusted or a series of surfaces with different types of roughness. A sidewalk simulator could also be developed that would allow WC riders to experience a wide range of surface profiles and report their comfort level.

Acknowledgment This work was supported by the U.S. Access Board.

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