TH€ LASER RST: CURRENT STATUS Peter W. Arnberg Michael W. Burke Swedish Road & Traffic Research Institute (VTI) OPQ Systems AB Linkoping, Sweden LinkOping, Sweden Georg Magnusson Roger Oberholtzer Swedish Road & Traffic Research Institute (VTI) OPQ Systems AB Linkoping, Sweden Linkoping, Sweden Knut Rkhs Leif Sjogren OPQ Systems AB Swedish Road & Traffic Research Institute (VTI) Linkoping, Sweden Linkoping, Sweden September 1991 About the Authors Peter W. Arnberg, Ph.D., is head of the Laser RST research group. He conceived the initial idea for the Laser RST system and directed its development at the Swedish Road and Traffic Research Institute (VTI). He was formerly Division Manager for the Laser RST system at RST Sweden AB but has recently returned to VTI. He also was head of research for the Saab RST. Michael W. Burke, M.A., M.Sc.I.E., (Ph.D. Systems Engineering, in progress), formerly an Assistant Professor of Industrial Engineering at New Mexico State University, was a visiting researcher at both VTI (1987,1988) and RST Sweden AB (1988). In 1990 he joined OPQ Systems AB as the project leader for the video hybrid system. Georg Magnusson, M.Sc. (Mechanical Engineering) is chief researcher and member of the Laser RST research group at VTI. His research in this area began in 1972 with studies of road comfort and roughness, conducted together with Peter W. Arnberg. Roger Oberholtzer, M.A. (Psychology) is responsible for the supervisory software in the Laser RST and for all data analysis software. He is Computer Systems Manager at RST Sweden AB and OPQ Systems AB. Knut Rcihs, M.Sc. (Electrical Engineering) isDirector of OPQ Systems AB, which manufac- tures electronic components and software for the Laser RST. Leif Sjdgren, (M.Sc. Electrical Engineering, in progress) is chief researcher and member of the Laser RST research group at VTI. Acknowledgements This report hasbeen supported by the National Swedish Road Administration. The authors are deeply indebted to Ms. Diana Burke, who designed and prepared the report, and to all the other people at VTI and OPQ Systems AB who contributed to its preparation. The authors also wish to thank Mr. Ramon Crespodel Rio of AEPO S.A., Spain; Dr. Rudolph R. Hegmon of the Federal Highway Administration, USA; Mr. Patrick G. Jordan of the Transport and Road Research Laboratory, UK; Dr. William D.O. Paterson of The World Bank, USA; Mr. Robert B. Smith of CMPS Pty Ltd, Australia; Dr. James C. Wambold of Pennsylvania Transportation Institute, USA; and other personnel at RST Sweden AB and VTI for their valuable comments and suggestions. Abstract Efficient and well-maintained road systems are necessary for the economic well being of any industrialized country. Maintenance and rehabilitation of existing roads have taken priority over new construction in recent years, thus making information about the condi- tion of road surfaces extremely important. Several methods of gathering this information have been developed worldwide; one of them is Laser Road Surface Tester (Laser RST), which was developed in Sweden in 1981. The Laser RST is a laser-based, computer-automated, non-contact road profilometer system with the ability to collect and simultaneously process data about the road surface. Variables measured include rut depth, unevenness, cracking, megatexture, rough macro- texture, fine macrotexture, crossfall, curves, and elapsed distance. Subjective evaluations are also supported, if desired. Eleven laser rangefinders (LRFs), mounted on the front of the Laser RST van, are the primary components of the data collection system. They scan the road with high-speed, high-resolution distance sampling. The signals from the lasers are sent through signal processing cards (SPCs) and then to a computer inside the van for final processing. Data is stored on floppy disk and printed by an on-board printer. The Laser RST is an extremely complex system but it is also a modular one, making troubleshooting and repair relatively easy, inexpensive, and fast. This paper discusses the various modules available. Variables measured are defined and measurement algorithms detailed. The Laser RST system can be customized to meet specific user requirements quickly and easily. Data from the Laser RST is used in various ways, depending on where and for whom the measurements are done. One example is as input data for Pavement Management Systems (PMS's). These computer programs use the data from the Laser RST about the road surface to generate a set of recommendations for the most cost-efficient road rehabilitation policy. The data format from the Laser RST can be tailored to interface with a wide variety of PMS's. RST Sweden AB has a PMS available for those customers who do not currently have one. The Laser RST data also interfaces well with the more traditional statistical databases. RST Sweden AB provides an extensive set of graphical tools and services for these customers as well. In Sweden, the Laser RST measures a significant portion of the roads every year; the data from these measurements is used by the Swedish National Road Administration and its Road Data Bank, which generates graphical and statistical information about the road system. The Laser RST is currently measuring or has measured roads in numerous other countries including Australia, Canada, Czechoslovakia, Denmark, England, Finland, France, Ger- many, Hungary, Iceland, New Zealand, Saudi Arabia, Spain, and the United States. Some of the results of these measurements are described. Future developments for the Laser RST include storage of raw data, video pattern process- ing for cracking classification, friction measurement, bearing capacity, and road visibility. Also planned are a high-performance research vehicle, road-edge scanner, and network-node marking. At present, the Laser RST is the only fully integrated road-surface measurement system available, collecting and directly evaluating all data on a large number of road condition variables simultaneously and at normal traffic speeds. Table of Contents List of Figures ix List of Tables List of Abbreviations xii Chapter 1: Introduction 1 1.1 Summary 1 1.2 Road Surface Testing: Purpose and Use 1 1.3 Road Surface Characteristics 2 1.4 Road Surface Testing Systems Currently in Use 4 1.5 Overview of Report 5 Chapter 2: The Laser RST Components 5 2.1 Summary 5 22 Overview of the Laser RST 5 2.3 Hardware 9 2.3.1 Laser Rangefinders (LRFs) 9 2.3.2 Accelerometers 11 2.3.3 Inclinometers 11 2.3.4 Rate Gyro 12 2.3.5 Pulse Generator 12 2.3.6 Electrical Compass 12 2.3.7 Supervisory Computer 13 2.3.8 Manual Input 13 2.3.9 System Power 14 2.4 Signal Processing Computer (SPC) Cards 15 2.5 The Driver/Operator 16 2.6 Data Input and Management 17 2.6.1 Data Storage and Analysis 17 2.6.2 Videologging 18 2.6.3 Report Variables 20 2.7 Maintenance and Calibration 22 2.7.1 Maintenance 22 2.7.2 Field Calibration 24 2.7.3 LRF Verification Control 25 2.8 Documentation 26 Chapter 3: Algorithms 27 3.1 Summary 27 3.2 Longitudinal Profile / Road Unevenness 27 3.2.1 Root Mean Square (RMS) 30 3.2.2 International Roughness Index (IRI) 30 3.2.3 MO 33 3.3 Cross Profile and Rut Depth 35 3.3.1 Laser RST's Cross Profile Measurements Compared to Stationary Methods 35 3.3.2 Calculation of Rut Depth 36 3.4 Texture 38 3.5 Cracking 42 3.6 Road Geometry 45 3.7 Algorithm Accuracy and Repeatability 50 Chapter 4: Measurements in Sweden 51 4.1 Summary 51 4.2 The Swedish Road Network 51 4.2.1 The Swedish National Road Administration (SNRA) 51 4.2.2 History of Road Measurement Under SNRA 56 4.2.3 Measuring Procedure 56 4.2.3.1 Planning 56 4.2.3.2 Production Measurements 56 4.2.3.3 Reliability Check 57 4.3 Swedish Road Data Bank 57 4.3.1 Reference System 59 4.3.2 Road Database 59 4.3.3 Alignment Database 60 4.3.4 Bridge Database 60 4.3.5 Pavement Database 60 4.3.6 Coordinate Database 61 4.3.7 Accident Database 61 4.4 Airfield Inspection 62 4.5 Calculation of Cut and Fill Volumes 62 4.6 Road Data Systems 64 4.6.1 Pavement Management Systems (PMS's) 64 4.6.2 Graphic Presentation System 68 4.6.3 Data Report Strategy 70 Chapter 5: The Laser RST in Other Countries 71 5.1 Summary 71 5.2 Australia 71 5.3 United States and Canada 73 5.4 England 73 5.5 Denmark 75 5.6 Spain 75 5.7 Hungary 75 5.8 Other Countries 75 Chapter 6: The Future 77 6.1 Summary 77 6.2 Storage of Raw Data 77 6.3 Friction Measurement 78 6.4 Road-Edge Scanner 78 6.5 Sight Distance 78 vl 6.6 Network Node Marking 80 6.7 Video System for Surface Distress Analysis 6.8 Research Laser RST 84 6.9 Bearing Capacity 86 6.10 Database Compatibility 88 Chapter 7: Epilogue 89 References Bibliography 84 \ List of Figures 2.1 The Laser RST 6 2.2 Characteristics of the Laser RST 6 2.3 The Laser RST principle 7 2.4 Overview of the Laser RST system 7 2.5 Schematic description of the Laser RST processing system 8 2.6 Measurement of macrotexture at six different speeds 9 2.7 Measurement variables 9 2.8 Laser measurement principle 10 2.9 Laser unit positions for the Laser RST (1987) from driver's viewpoint 10 2.10 Manual input to the supervisory computer 14 2.11 Road distance transmitter (pulse transducer) 16 2.12 Course for drivers 17 2.13 Layout of the videologging system V-RST 19 2.14 Two cameras used in the videologging system 19 2.15 Video equipment used in the videologging system 20 2.16 The output pictures from the V-RST 20 2.17 Printout from a survey done in Stockholm 21 2.18 Example of a printout available directly from the Laser RST 23 2.19 Calibration of the LRFs 24 2.20 Laser test stand 25 2.21 Test surface