Royal Institute of Technology Scania CV AB Division of Industrial Ergonomics Vehicle Ergonomics A laboratory vehicle mock-up research work on truck driver’s seat position and posture A mathematical model approach with respect to anthropometry, body landmark locations and discomfort Doctoral thesis By: Kianoush Fatollahzadeh Stockholm, Sweden, 2006 Kianoush Fatollahzadeh Stockholm 2006 Royal Institute of Technology Department of Industrial Economics and Management Division of Industrial Ergonomics Lindstedtsvägen 30 S-100 44 Stockholm TRITA-IEO R 2006:8 ISSN 1100-7982 ISRN KTH/IEO/R- 06/08--SE ISBN 91-7178-361-X For Nancy, Aryamen and Armen ABSTRACT Professional truck drivers are highly exposed to fatigue and work related injuries. Truck drivers are common victims of musculoskeletal disorders, frequently suffering from pain symptoms particularly in the neck, shoulder and lower back. This situation is believed to be a contributor to the high absenteeism in this job category. A high percentage of this problem is due to the adoption of an unhealthy driving posture resulting from inappropriate seat design. This incorrect and poor design is owing to the insufficient and obsolete anthropometrical data which has been used for decades for arranging and positioning components in the driver environment. The main objective of the present study was to create and construct a mathematical model which clarifies and predicts the drivers’ comfortable sitting posture and position. It was hypothesized that the length and height characteristics of some body segments as well as the body weight and waist circumference of the driver have a great impact on the selection of a specific sitting posture. The steering wheel positions as well as the pedal/floor locations were hypothesized to be highly correlated to the driver’s selected posture and the corresponding comfort. The effect of the seat position on posture selection and related comfort assessments constituted the other hypothesis of the study which received extra attention. A laboratory experiment on a Scania truck cab mock-up was conducted. The seat track travel along a vertical as well as horizontal forward-backward path was obtained by mounting the seat on the motorized rigid frame which allowed unrestricted vertical and fore-aft travel. The seat cushion angle and backrest angle were adjusted by pivoting the entire seat and backrest around a lateral axis and independently. The pedal components were mounted on a motorized platform, thus allowing unrestricted fore-aft and height travel without any changes in the pedal angles. The steering wheel was mounted on the instrument panel by two independent pneumatic axes which allowed a wide range of adjustments including tilting and moving along the sagittal plane for adjusting the height and distance. The test plan called for 55 international highly experienced heavy truck drivers. The drivers were recruited to span a large range of body weight and stature, in particular to ensure adequate representation of both the extreme as well as the normal group of drivers. The drivers filled in a general information questionnaire before undergoing the anthropometrical measurements and thereafter the test trials. The experiment contained a subset of test conditions with five different trials using random selection sampling procedure. Drivers were asked to adjust the components in a wide range of trajectory according to a written protocol. A sparse set of three- dimensional body landmark locations and the corresponding comfort assessments were recorded. As the main part of the result, the mathematical models using multiple regression analyses on selected body landmarks as well as anthropometrical measures were developed which proposed a linear correlation between parameters. The differences between the observed data and the corresponding predicted data using the model were found to be minimal and almost dispensable. Additionally, the drivers preferred to sit in the rearmost position and at a rather high level relative to the rest of the available and adjustable area. Considering the normal adjustable seat area of the cab, only a very small part of the observed H- point data lies within this area while a large remaining amount of data lies outside of it. Moreover, the difference between the observation (plotted H-point data) and the neutral H-point was found to be significant. Furthermore, and since some of the data lies almost on the border of the adjustable area, it may indicate a reasonable tendency for even more seat adjustment in the backward direction. A conceptual model consisting of four different parameters was developed and presented in the end. These parameters of the model suggest being as key factors which play a central role on process of decision making regarding the selection of a desirable sitting posture. Any eventual modifications and adjustments for elimination or minimizing discrepancies, biases or obscured factors affecting the quality of the mathematical model would be a case for future study. The investigation of a complete assessment of comfort should be supplemented with an analysis of how many truck drivers are satisfied with the comfort in the end. Key words: truck driving, anthropometry, body landmarks, discomfort, sitting posture Abbreviations and Acronyms AHP Accelerator Heel Point ASIS Anterior-Superior Iliac Spine BL Body Landmarks BMI Body Mass Index BOF Ball Of Foot CPM Cascade Prediction Model EEG Electroencephalography EMG Electromyography H30 dimension Seat height H-point Hip joint IPM Independent Prediction Model L5 Lower lumbar spine LFC Lateral Fumeral Condyle LHC Lateral Humeral Condyle NHTSA US National Highway Traffic Safety Administration NIOSH National Organisation Safety and Health OPM Optimization Prediction Model PD Pelvis Depth PD-process Product Development process PH Pelvis Height PSIS Posterior-Superior Iliac Spine PW Pelvis Width R- point (SgRP) Seating Reference Point SAC Science Accessories Corporation SAE Society of Automotive Engineer SPSS Statistical Product and Service Solution SRC Subjective Rating of Comfort including questions: Ratavstånd = STW distance Rathöjd = STW height Ratvinkel = STW angle Sithöjd = Seat height Sitvink = Seat angle Rygvink = Backrest angle Golvplac = Floor level Gasped = Accelerator Kopplin = Clutch level Helhet = Overall feeling STW Steering Wheel VIMS Vehicle Interior Measurement System 1 Background Truck driving is not an easy occupation, rather it can be considered one of the most dangerous professions, annually taking many lives in highway and long distance accidents as well as along local routes and in city traffic violations. The range of injuries and fatalities which occur mostly in rollover accidents is even more extensive when driving certain types of rigs such as tankers and flatbeds, known as probably one of the most dangerous major occupations. Whatever the type of heavy duty vehicle, as far as the working condition of truck driver is concerned, two major types of problems may arise. The first one, as stated above, can be classified as Traffic Related Accidents such as fatalities and injuries in various traffic situations. The second type supposedly belongs to general ergonomical issues directly related to the psycho-physiological working condition of truck drivers and can be classified as Work Related Symptoms i.e. musculoskeletal disorders and pains, symptoms of stress, etc. The present study will consider the latter concept (Work Related Symptoms) and deal with this issue in more detail. A clarification of these issues are summarized in the following table Table 1-1. Categories of health related risks Risks Traffic Related Accidents Work Related Symptoms general ergonomical issues Type of fatalities and injuries in various traffic psycho-physiological injuries situations working condition of truck drivers musculoskeletal disorders and pains, symptoms of stress, etc. Considerd XXX Work Related Symptoms in study 1.1 Drivers’ Work Related Symptoms Vehicle drivers are seriously exposed to various types of work load such as environmental and psycho-physiological problems while they are engaged in driving activities. In studies by Gyi and Porter, 1998 as well as Porter and Gyi, 2002, professional drivers are considered to be highly exposed to work related injuries. These injuries comprise musculoskeletal disorders mostly concentrated on upper extremities such as the neck, the shoulder but also the lower back. The problems are more severe for long haulage drivers who continuously work in a relatively static posture while interacting with the vehicle as well as the surrounding environment. These job characteristics make the driving task simultaneously monotonous and complex from the psycho-physiological point of view. Work related complaints from drivers regarding the problems of both long- term and short-term effects with respect to the physical and psychological requirements 1 imposed by driving tasks have been a subject of interest in the research world. Problems with the long-term effects such as health, safety and workload and those of short-term effects including the abilities and competence to perform the tasks are typical issues regarding this occupation. Noise and vibration, musculoskeletal pain and fatigue resulting from tiredness and losing alertness, etc are other more specific examples and are encountered as significant factors influencing driving performance. Regarding musculoskeletal complaints, truck drivers are common victims of back problems, being