Accelerometer Method of Riding-Quality Testing

At a meeting of Highway Research Board Committee D-B4 last January, R. L. Rizenbergs presented an oral description of our development of the accelerometer method of measuring road roughness; and representatives from several state highway departments expressed an interest in duplicating our instrumentation. It became incumbent upon us then to prepare a more formal description for distribution to the Committee and other interested parties. The report submitted herewith is intended to fulfill that purpose. No specific action is requested. Copies are furnished for information only

Analysis of Pavement Roughness

In earlier progress reports dealing with the development of triaxial acceleration analysis as applied to the evaluation of pavement riding qualities, of which this report is a continuation, riding comfort or discomfort was emphasized. The accelerations monitored then were evaluated in terms of g\u27s per sec., or jerk which is considered by some authorities to be a more significant index of comfort. The earlier methods of analysis have been reviewed, and acceleration is considered here to be the most practical parameter to use as a measure of pavement roughness. Most of the equipment and instrumentation has been retained, and the recording of triaxial accelerations has been continued. However, only accelerations in the vertical direction are considered in the present method of analysis. In the summer of 1957, some 265 miles of bituminous concrete pavements were recorded and analyzed as part of a study on flexible pavement design. Since then, some 1000 additional miles of bituminous and portland cement concrete pavements have been tested. These include some older pavements, newly constructed pavements, and Inter-state sections thus far completed. Some of the roads have been re-tested periodically. These roads represent a cross section of Kentucky pavements and give an indication of the status of pavement roughness from the standpoint of workmanship on new pavements, rate of deterioration, and the effects of re-surfacing

Discussion on Skid Resistance of Pavement Surfaces

The concern for adequate skid resistance or friction of pavement surfaces is confined to wet weather conditions. Dry pavements are highly skid resistant unless the surface contains loose material, such as gravel, sand, etc., which could provide rolling action by the particles under the tires. Surface contaminates, such as oil, soft tars and asphalt, etc., could also provide lubrication to the surface and create a slippery condition. Normally, however, water is the lubricating agent reducing pavement friction and in some cases creating very hazardous driving conditions. Another situation of concern is drainage, or lack of proper drainage, of the pavement. Excessive water depth may cause the vehicle tires to hydroplane, i.e., the tires may become separated from the surface and ride partially or entirely on a water layer, thus causing loss of traction. Both of these conditions will be discussed in detail

Florida Skid Correlation Study of 1967 – Skid Testing with Automobiles

The inclusion of automobiles in the Florida skid correlation study was promoted by the recognition of the following needs: 1) to compare stopping-distance measurements obtained with different instrumentation, 2) to suggest a standard method of stopping-distance testing, 3) to relate skid-resistance measurements of trailer-type testers with stopping distances of automobiles, and 4) to explore other skid-resistance measurements techniques using an automobile. The vehicles were all full-size automobiles. Each vehicle was instrumented to measure a distance from a predetermined pressure in the brake hydraulic system to where the vehicle came to rest. Stopping distance in most of the automobiles was read directly from summating counters. Two of the automobiles were equipped with strip-chart recorders to measure distance, velocity and deceleration during the skid. The measured stopping distances displayed minor differences between automobiles regardless of the instrumentation. The primary cause of variation in the test results was attributed to the ability of the driver to apply brakes at the prescribed test velocity. Lag between brake application and wheel lock and errors in the distance-measurement instrumentation were of secondary concern. The stopping-distance data were correlated with the trailer-measured skid resistances for several velocities. Approximate stopping distance, therefore, can be predicted from trailer tests, or vice versa. The results of the stopping-distance tests were sufficiently encouraging to consider standardization. Adoption of a standard method of test would serve several useful purposes. The principal benefits would be derived from having a reliable, alternate method of skid testing and references to stopping distance of automobiles would acquire a uniform understanding of the measurement and, therefore, common usage of the term

High-Intensity Reflective Materials for Signs

Field observations and laboratory tests and evaluations were conducted on High-Intensity and Engineering Grade materials (Scotchlite), manufactured by the Minnesota Mining and Manufacturing Company, and were compared in regard to reflectivity, durability, and cost. The High-Intensity Grade materials were found to have outstanding performance characteristics in comparison to Engineering Grade materials. The material significantly enhances sign legibility under low-beam illumination, and accelerated weathering tests showed superior durability

A Survey of Reflective Sheeting for Highway Signs

A questionnaire (see the APPENDIX) was sent to highway agencies in all 50 states, the District of Columbia and Puerto Rico for the purpose of surveying state practices in regard to reflective sheeting purchase, usage specifications, testing, etc. The response was 100 percent and, thus, demonstrated a high degree of interest in the subject. Responses to the questionnaire are tabulated on the attached tables. An attempt was made to report answers provided by the agencies without interpretation except in a few isolated cases where the necessafy information was available to properly relate the response to a given question. In a few instances, the agency was contacted for additional information or clarifications. A detailed analysis of information obtained from the questionnaire, copies of specifications and purchase requisitions submitted by the respondents is intently omitted here. Instead, each contributor is invited to review the attached tables and to extract whatever information may be of value. However, the commentary and summary of findings, which follows, may be of interest

Pavement Roughness Studies (A Progress Report)

Road roughness testing in Kentucky was first reported in 1949 (1). At that time, emphasis was placed on localized irregularities in pavement profiles detectable by a roller-type straight edge. The experience gained then pointed to the necessity for making a fast, continuous recording of characteristics of the road which would be more closely related to riding quality. Subsequent progress reports (2)(3) dealing with the development of triaxial acceleration as applied to the evaluation of pavement riding qualities emphasized riding comfort or discomfort. The accelerations monitored then were evaluated in terms of g\u27s per seconds or jerk , which is considered by some authorities to be a more significant index of comfort. This earlier method of analysis was later reviewed, and the resultant report (4) in 1961, of which this report is a continuation, considered acceleration in g\u27s to be the most practical parameter to use in describing pavement roughness. However, only the accelerations in the vertical direction are considered in the present method of analysis. The previous reports contain descriptions of instruments and methods of recording roughness and of determining roughness indexes

High-Intensity Reflective Materials for Signs

The intuitive need for improved sign legibility has increased through the years as traffic volumes, speeds and roadway designs have advanced. Because of increased traffic volumes, low-beam headlight illumination at night has become more imperative. Signs are being located farther from the travelled lanes; higher speeds are requiring messages to be more legible at greater distances (for driver decision and response). Recent studies have indicated that even Engineering Grade (2200 and 3200 Series) Scotchlite or materials designated as Type I, Class A in S.P. No. 89-A, may be inadequate for some signing situations. Signs may be made larger and(or) incorporate materials which are brighter. Thus far, neither brightness nor sign size has exceeded optimum. Obviously, economics and other considerations come into issue

High-Intensity Reflective Materials for Signs

Field observations and laboratory tests and evaluations were conducted on High-Intensity and Engineering grade materials (Scotchlite), manufactured by the Minnesota Mining and Manufacturing Company, and were compared in regard to reflectivity, durability, and cost. The High-Intensity type materials were found to have outstanding performance characteristics in comparison to Engineering Grade materials. The material significantly enhances sign legibility under low-beam illumination, and accelerated weathering tests showed superior durability

Frictional Performance of Pavements and Estimates of Accident Probability [Dec. 1980]

Objectives of this study were to evaluate standard and experimental surfaces throughout Kentucky in terms of skid resistance and effects of traffic, and to provide criteria for judging suitability of these surfaces to satisfy requirements for skid resistance and economics. The effects of traffic were quantified by regression analysis and scatter of data. Criteria included an estimate of accident risks, effects of speed on skid resistance, and seasonal variations in skid resistance. Pavements on low volume roads (less than 1,000 vehicles per day) maintained adequate skid resistances. Open-graded friction courses, with the possible exception of sections using phosphate slag aggregate, maintained adequate skid resistance to meet design requirements. The adequacy of other pavements may be judged from the criteria provided herein. Estimates of accident reduction were made by combining the relationship between skid numbers and accidents with the distribution of skid numbers for each pavement type. Those reductions were used to calculate benefits that, along with costs of overlay, were used to determine benefit-cost ratios. Benefits exceeded costs for roads having AADT\u27s greater than 750, 2,500, and 5,000 and SN\u27s less than 24, 30, and 35, respectively