A Synopsis on the Current Equipment Used for Measuring Pavement Smoothness

By Joseph Budras P.E. - August 2001

Introduction
Current Equipment Used in Measuring Pavement Smoothness

Appendix A - Glossary

Appendix B - Bibliography

Appendix C - A Partial List of Equipment Manufacturers/Vendors

Introduction

During the early years of road construction in the United States, pavement smoothness was not a primary consideration for paving operations. It was assumed that the contractor would produce a pavement with acceptable smoothness. Since these early days, studies have confirmed that highway users judge the condition of the highway system primarily by the ride that they experience when traveling over the roadway. The most recent study was a 1996 Federal Highway Administration (FHWA) national survey of frequent public highway users throughout the country. This study confirmed that road condition was the top priority regarding what highway users were looking for in their highway product. Research as shown that smooth roads cost the highway agencies less over the life of the pavement resulting in decreased highway user operating costs.

With the highway users' national emphasis on pavement smoothness, FHWA has set a performance goal to significantly improve the quality of measured pavement smoothness of the National Highway System by 2008. We cannot improve pavement smoothness across the U.S. without the instrumental involvement of all FHWA employees. This includes not just pavement specialists, but also planners, marketers, program and quality coordinators, policy development specialists, and public affairs specialists. Each of these specialties is involved in some component of FHWA's strategic Mobility Goal of which pavement smoothness constitutes an integral part.

With the agency-wide attention on measuring the progress toward attaining pavement smoothness, it is believed that professionals in non-pavement related fields would benefit from becoming acquainted with the current equipment used to measure pavement smoothness. To that end, this document is intended to inform the non-pavement specialist of the various devices used for measuring pavement smoothness. This synopsis provides information on the equipment, characteristics, capabilities, and costs. It is not meant to elaborate on the technical aspects of measuring pavement smoothness. For this type of detailed technical information, a bibliography, as well as a partial listing of equipment manufacturers and vendors are provided at the back of the document. The inclusion or omission of any particular device or manufacturer/vendor should not be construed as an endorsement or disapproval.

Pavement smoothness data collection has several applications. Essentially it consists of: 1) to evaluate the quality of newly constructed or repair sections, 2) to study the conditions of specific sites for research, 3) to diagnose the condition of specific sites and determine the appropriate remedies, and 4) to monitor the condition of a road network for pavement management systems (PMS). When reading this document, it is important to realize that pavement smoothness (or degree of smoothness) is related only to the vertical changes in the level of the road in the wheelpaths of the vehicle, measured as a summary of vertical deviations that occur over an interval between two points.
Current Equipment Used in Measuring Pavement Smoothness
1. Profilographs
  
  The profilograph is used to measure the longitudinal profile of a concrete pavement. Its principle use has been for the construction control of pavements. Profilographs have successfully been used for construction quality control on thousands of miles of pavements over the last several decades. In the mid-1980's, computerized data collection was introduced to record and analyze the pavement surface profile. With most states using profilographs for measuring smoothness, the profile index has become a standard index for smoothness measurement in construction specifications.
  
  Two basic types of profilographs have evolved, each with different support wheel configuration, the California type profilograph, and the Rainhart type profilograph. The profilographs are relatively inexpensive, simple to operate and maintain, and provides a trace of surface users can easily understand. Both are manually operated by one person at walking speed; however, because of its wheel linkage, it can not be used for high speed network pavement smoothness data collection. Support wheels on the California type profilograph have varied in number from four to twelve, with systems in many States using twelve wheels. These wheels are attached to the ends of a 25 foot (7.6m) long truss and mounted on a multiple axle carriage that includes four wheels spaced 17 inches (432mm) from the truss centerline and two wheels spaced 17 inches (432mm) on the opposite side of the truss centerline. The support wheels are commonly spaced at 2.7 feet (0.82m) intervals and positioned near the ends of the truss, resulting in an overall profilograph span of approximately 33 feet (10m).
  
  The Rainhart profilograph operates similar to the California profilograph. The major difference is that the Rainhart uses twelve wheels arranged in four groups of three. This wheel arrangement ensures that each wheel travels a separate path. This allows measurement of twelve wheel paths instead of just three as with the California profilograph.
  
  With the advent of non-contact lightweight profilers, the profilograph may become most suited to retest short defective pavement sections for verifying the correction of such defects. Profilographs are also highly suited to bridge deck testing, as those jobs require only a short profile distance.
  
  The device is currently available from the following firms: Cox and Sons, Surface Systems Instruments, Ames Engineering, and ELE International-Soiltest. It sells for approximately $25,000 depending on the manufacturer.
  
  The following page contains illustrates the two different types of profilographs.
  
  Key terms: longitudinal profile, network, profile index
  
  CALIFORNIA PROFILOGRAPH
  side view
  
  RAINHART PROFILOGRAPH
  side view
2. Response-Type Road Roughness Measuring System
  
  For many years, most network pavement smoothness data was obtained with vehicles instrumented with road meters, call by several generic names including: "response-type road roughness measuring systems" (RTRRMS). RTRRMS operate at highway speeds, these devices are mounted in a vehicle, light truck, or special trailer. The RTRRMS measure the response (bounce) of the vehicle to the road smoothness, it is therefore not a true measurement of smoothness. Included in this category of equipment are devices that measure the relative axle-body motion and devices that measure the acceleration of the axle or the vehicle body.
  
  The Mays Ride Meter has been by far the most commonly used. This device determines the smoothness of the roadway by measuring the displacement between the axle housing and the body of the host vehicle. The method actually measures the relative motion of the sprung mass system in response to traveled surface smoothness where the mass is supported by the automobile type suspension and tires. The operation requires a two-person crew.
  
  The major components of the Mays Ride Meter are the rotary transducer, the pavement condition recorder, and the distance measuring instrument. The rotary transducer converts the axle/body movement to an electrical signal. The distance measuring instrument is an electronic odometer. The pavement condition recorder is a microprocessor, which accepts input from the rotary transducer, the distance measuring instrument, and the keyboard processes the various signals into an output. This output is commonly in the form of accumulated inches of relative motion over a distance.
  
  Road meters were devised to be cheap, rugged, and easy to use. Therefore, the fact that the response-type system depends on the dynamics of the host vehicle has several negative affects: Smoothness measuring methods have not been stable with time. Measurements made today with road meters cannot be compared with confidence to those made several years ago. Also, smoothness measurements have not been transportable. Road meter measurements made by one system are seldom reproducible by another.
  
  In spite of these and other problems associated with response-type meters, they have been in use for the past 50 years and even with the advent of non-contact profilers, a handful of states still use the Mays Road Meter. One reason this device has been in use for so long is that it has convinced engineers that this profiling method has produced meaningful pavement smoothness measurements.
  
  The cost of the Mays Ride Meter Trailer and associated strip chart recorder is about $8000. The price of the Pavement Condition Recorder is about $10,000. The prices vary depending on the manufacturer. The following page illustrates the Mays Ride Meter
  
  Key terms: transducer
  
  A car with a Mays Meter
3. Road Roughness Profiling Devices
  
  Profiling devices are quite common for network pavement data collection, however, they are not designed for project level quality control. They measure and record the longitudinal profile in one or both wheel tracks. In the U.S. the inertial type of profiling devices are used. Devices in this category of equipment include the K. J. Law Profilometer (K.J. Law's patented name for the profiler) and the South Dakota profiling device.
  
  Inertial profilometers are capable of measuring and recording road surface profiles for network use at speeds between 10 and 70 miles per hour (16 and 112 kph). The profilometer measures and computes the longitudinal profile of the pavement through the creation of an inertial reference by using accelerometers placed on the body of the measuring vehicle. Relative displacement between the accelerometers and the pavement surface is measured with a non-contact light or acoustic measuring system mounted with the accelerometer on the vehicle body.
  
  Operation requires a two-person crew, one as a vehicle driver and the other as a system operator. The entire system is mounted in a full size van. The profile computer, data recording and other system components are all contained in the vehicle. The profilometer contains sensors for measuring road surface profile and rut depth. The accelerometers establish the reference plane for the profilometer system's measurement by measuring the vertical accelerations of the vehicle body. The distance traveled by the system is measured with a distance encoder. This is usually a pulse type distance measuring device which is mounted to the front wheel of the vehicle.
  
  The profile signal processing is performed by a digital computer mounted in the vehicle. Profile computations are performed in real time as the vehicle is driven down the road. Interface between the user and the profilometer system is provided through a system terminal and printer.
  
  Pavement profile data points, taken every inch (centimeter), are averaged over a running 12-inch interval and stored as profile points for every 1, 2, or 6 inches (25, 50, 150 millimeters) of travel. The program for rut depth computes and stores average rut depth taken every 100 feet (55 meters) from data taken every 3 feet (1.6 meters), or at other selected points.
  
  Vehicle response simulation programs for smoothness index calculations are available with the profilometer system. The selected roughness index is normalized to read inches per mile and is printed out on the system printer. Metric (SI) programs are also available.
  
  The cost of a non-contact inertial profilometer varies with the level of precision. The K.J. Law profilometer is the most precise device and is available from K.J. Law Engineers for about $160,000 to $220,000 depending on the options. The South Dakota device contains less inexpensive ultrasonic sensors, which are less precise. It measures the profile in one wheel path and rut depth. The South Dakota device is estimated to cost $50,000 depending on the manufacturer.
  
  Key terms: accelerometer, non-contact sensor, rut depth
  
  Photo of road roughness profilometer van
  
  Schematic of road roughness profilometer van
4. Non-Contact Lightweight Profiling Devices
  
  A new generation of lightweight non-contact profilers have emerged for construction quality control and quality acceptance purposes. They are much smaller and lighter than the network level profilers, providing the benefit of use immediately after hot-mix asphalt (HMA) construction and much sooner than would be possible with the network level devices on new portland cement concrete (PCC) pavements. However, they have operating speeds ranging from 8 (13km) to 25 miles (40km) per hour, which makes it impractical for high speed, large road network data collection. These non-contact profilers require a one to two person operation, some are battery powered, others have gasoline engines. The basic system consists of an accelerometer, a non-contact sensor distance measuring instrument, a graphic display, an IBM-compatible PC, with a graphics printer. Inputs from the accelerometer and non-contact sensor are fed to the system's on-board computer, which calculates and stores a user selected smoothness index, and capable of storing as much as 13,000 miles (21,000km) of data. Pavement profile data points, taken every inch, are averaged over a running 12-inch (305mm) interval and stored as profile points every 6 inches (152mm), or every inch if required. The results can be viewed on-screen or output to the printer. The longitudinal measurements are independent of variations in vehicle weight, speed, extremes in temperature, sunlight, wind, and pavement color or texture. They can also calculate different smoothness indices using the same data. Some of the emerging profilers include the Lightweight Profiler T6400, manufactured by K.J. Law; Liteweight Inertial Surface Analyzer (LISA), manufactured by Ames Engineering; and the Lightweight Profiler, manufactured by International Cybernetics Corporation; Surface Systems Inc, and Pathway Services, Inc. also manufacture lightweight profilers. The profilers sell from approximately $45,000-$60,000 depending on the manufacturer.
  
  non-contact lightweight profiler
  non-contact sensor
5. Portable Laser Profiler Systems
  
  For road network data collection, the Multi-Laser Profiler (MLP) provides a vehicle mounted system that automatically collects integrated road condition data by recording laser profilers of the road surface at highway speed. It is very useful for monitoring large road networks. The speed of operation ranges from 18 miles (29km) to 75 miles (120km) per hour. The MLP requires a two person operation and comes with an on board computer system and a range of software for data acquisition and analysis tasks. It simultaneously measures surface smoothness in IRI, rutting depth and macro texture in both longitudinal and transverse profiles. The inertial sensors compensate for suspension and tire characteristics. It surveys up to approximately 370 miles (600km) of road per day at intervals as close as two inches (50mm) for smoothness rutting and approximately 1/4 inch (6mm) for texture.
  
  Portable laser profiler systems contain many other sensors and modules not required for pavement smoothness measurement. Among these optional features of the system include a global positioning system, a road alignment data and digital mapping system, and a voice defect logging which allows an operator to log road defects while driving. These optional features provide framework data for asset management. Trigg Industries, Inc., and Pathway Services are among the manufacturers of the MLP. The cost is approximately $75,000 depending on the manufacturer. Smaller, less expensive portable devices, such as light weight profilers are better suited for quality control in road construction.
  
  Multi-laser profiler vehicle
  
  An emerging automated portable laser profiler measurement system is the ROSAN. The ROSAN stands for Road Surface Analyzer. Originally designed by FHWA, the ROSAN serves as a vehicle mounted portable system for measuring longitudinal pavement profile depth at highway speeds, preferably over 30 miles (48km) per hour. This system is suited for measurement of texture and smoothness. The texture measurements are performed at a 0.25mm (0.010inch) sampling interval and are limited to a speed of 15 miles (24km) per hour. The ROSAN system relies upon software to register these measurements. The ROSAN requires a vehicle with a step bumper. The entire package, excluding the notebook computer, fits in a wheeled protective case. The ROSAN can be purchased as a complete system from Surfan Engineering for approximately $50,000. The operators attend a 2 ½ day training to learn the operation of the ROSAN. At this time, FHWA's Eastern Federal Lands is its main user.
  
  Key terms: macro texture, sampling interval
  
  Rosan System

Appendix A - Glossary

Accelerometer - is a sensor that measures acceleration

International Smoothness Index (IRI) - is recognized as a general purpose smoothness index. It summarizes the smoothness qualities that impact vehicle response.The IRI was created to provide a universal rating for the international pavement community. Almost every automated road profiling system includes software to calculate the IRI.The IRI is expressed in units of inches/mile (in/mi) and meters/ kilometer (m/km).

Longitudinal profile - is a two-dimensional slide of the road surface, taken along an imaginary line which show the design grade, smoothness, and texture. Refer to the figure below:

Schematic of road surface showing longitudinal and lateral profiles

Macro texture - is the feature of the road surface that ultimately determines most tire/road interactions, including noise and tire wear.

Network - the configuration of highways that constitutes the total system.

Non-contact sensor - determines the vehicle to road displacement for computation of longitudinal profile.

Profile index (PI) - is derived from the profilograph output. PI is expressed in units of inches per mile (in/mile) or millimeters per kilometer (mm/km).

Rut depth - the depth of a track worn out by the habitual passage of traffic wheels.

Smoothness indices - measure different ranges of wavelengths based on specific profilers. IRI and PI are among the two most common pavement smoothness indices.

Sampling interval - is the longitudinal distance between points that are digitized for computation of profile.

Transducer - a device that is actuated by power from one system and supplies power usually in another form to a second system.

Appendix B - Bibliography

Sayers, M.W. and S.M. Karamihas, The Little Book of Profiling, The University of Michigan Transportation Research Institute, September 1998.

Evaluation of Lightweight Non Contact Profilers, FHWA/IN/JTRP-2000/6, Indiana Department of Transportation/Purdue University, July 2000.

Guidelines for Conducting and Calibrating Road Smoothness Measurements, World Bank Technical Paper Number 46, 1986

Operational Guidelines for Longitudinal Pavement Profile Measurement, NCHRP Project 10-47, The University of Michigan Transportation Research Institute, February 1999.

Profile Equipment Evaluation, Research Report 1378-2, Texas Transportation Institute, December 1997.

Profilograph Limitations, Correlations, and Calibration Criteria for Effective Performance-Based Specifications, NCHRP Project 20-7, Task 53, 1993

A special thanks to the following companies/organizations for providing material:

Ames Engineering

K. J. Law Engineers, Inc.

Surface Systems & Instruments

Trigg Industries Intl., Inc.

University of Michigan Transportation Research Institute

Appendix C - A Partial List of Equipment Manufacturers and Vendors

Profilographs, Profilers and Non-Contact Lightweight Profiling Devices:

K. J. Law Engineers, Inc.
42300 W. Nine Mile Road
Novi, Michigan 48375-4103
Tel: 800-521-5245
Fax: 248-347-3345

James Cox and Sons
1085 Alpine Way
Colifax, CA 95722
Tel: 530-346-8322
Fax: 530-346-6854
www.jamescoxandsons.com

International Cybernetics Corporation
P.O. Box 17246
Clearwater, Florida 33762
Tel: 727-547-0696
Fax: 727-547-0251
www.internationalcybernetics.com

ELE International, Inc
2421 Highway 11
Pelham, AL 35124
Tel: 800-323-1242
Fax: 205-620-5558
www.soiltest.com

Ames Engineering
Box 310
Ames, Iowa 5010
Tel: 800-205-6355
Fax: 515-432-1656
www.amesengineering.com

Surface Systems & Instruments
304 S. Wisconsin Avenue
P.O. Box 404
Medford, Wisconsin 54451
Tel: 800-662-5656
Fax: 415-332-2909
www.ssi-profile.com

Portable Laser Profiler Systems:

Trigg Industries Intl., Inc
7007 Willoughby Avenue
Los Angeles, California 90038
Tel: 323-845-9390
Fax: 323-845-9503
www.triggindustries.com

Surfan Engineering and Software, Inc
3504 Littledale Road
Kensington, MD 20895
Tel: 803-506-2791
Fax: 803-506-2198

PathRunner Services, Inc.
P.O. Box 513
Noble, OK 73068
Tel: 800-234-0811
Fax: 405-872-9773
www.pathwayservices.com