Sponsoring Agency Code Supplementary NotesPrepared in cooperation with the Indiana Department of Transportation and Federal Highway Administration. AbstractThis study investigated many important issues associate with pavement surface friction testing, in particular using the smooth tire. This study utilized 3-D FEM program to investigate the fundamental friction phenomenon in light of energy dissipation during friction process. It was demonstrated that the pavement friction depends on many factors such as test tire, test speed, surrounding conditions, pavement surface texture, and pavement type. A great amount of friction data has been collected so as to investigate variations involved in pavement friction measurements. System variations depend on the feature of pavement surface. The standard deviations due to system errors are usually less than 5. The smooth tire tends to provide greater variations than the ribbed tire. As air temperature increases, the friction number does not necessarily decrease. No consistent relations were identified between friction measurements and test seasons. Seasonal friction variations are negligible. The largest directional variation is 16 with the smooth tire on a State road. The State and U.S. roads tend to produce greater directional variations than the interstates. Driving lane usually has lower friction than other lanes. The greatest lateral variation arose due to the effect of wheel track. Longitudinal friction variations depend on traffic distribution, pavement type, and surrounding conditions. Friction measurements taken at 1.0-mile spacing can provide realistic network pavement friction information. Pavement frictions on interstates decreased faster than those on State and US roads. INDOT conducts pavement inventory friction test every year on interstates and every three years on State and US roads.The force transducers should be calibrated every month and the whole system performance verified every week so as to identify potential significant performance changes. A minimum of three to five test runs must be conducted for system verification. The standard smooth tire is recommended for INDOT network pavement inventory friction test. In general, the friction number measured with the ribbed tire is greater than that with the smooth tire. However, the differences decrease as the surface texture becomes rougher. The average friction difference is about 20 on highway pavements. Friction test speed should be determined in light of the traffic conditions. Three test speeds of 30 mph, 40 mph, and 50 mph are recommended for network pavement inventory friction testing. Determination of the minimum friction requirement should consider its impact on wet-pavement accidents and agency's budgets. Taking into account the minimum friction requirement recommended by NCHRP Report-37 and the differences between the ribbed and smooth tires, a friction number of 20 with the smooth tire at 40 mph is recommended as the minimum friction requirement for network pavement inventory friction testing. ...
The use of Global Positioning System (GPS) technologies has expanded to perform traffic data collection for transportation studies such as work zone studies. To generate reliable results from the data acquired by using GPS devices, it is necessary to investigate such factors as sample size requirements that may affect a specific study and to establish a consistent method for data collection. It has been confirmed that the Institute of Transportation Engineers’ Manual of Transportation Engineering Studies usually underestimates the sample sizes for travel time and delay studies. However, the hybrid method developed by Quiroga and Darcy overestimates the sample sizes. A modified equation is presented to estimate the minimum sample sizes for collecting field data with GPS devices. Travel speed may be more stable and can be easily measured for travel time and delay studies. Stopped delay varies considerably at intersections, and the sample sizes depend to a large extent on the permitted errors. Work zone layout and construction activities will create variations in vehicle flow within the work zone. To estimate the sample size requirements, it is advisable to use the standard deviation to measure the data dispersion, and a minimum of three initial test runs is required. GPS devices with sufficient accuracy usually require 5 to 10 samples for travel time and delay studies and work zone studies. Stopped delay studies may require a large sample of up to 30 test runs.
The contents of this report reflect the views of the author who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Indiana Department of Transportation or the Federal Highway Administration at the time of publication. This report does not constitute a standard, specification, or regulation.
The contents of this report reflect the views of the authors who are responsible for the facts and the accuracy of the data presented. The contents do not necessarily reflect the official views or policies of the Federal Highway Administration and the Indiana Department of Transportation. This report does not constitute a standard, specification or regulation.
Some researchers have investigated the evaluation of pavement friction using macrotexture measurements and found that the relationship between friction and macrotexture is extremely weak. Textures that affect surface friction include both macrotexture and microtexture. While macrotexture can be readily measured at highway speeds currently, micro-texture is evaluated by the friction from a surrogate device at low speeds. Microtexture depends mainly on the surface properties of the aggregates and plays an important role in developing friction force. The evaluation of pavement friction solely from texture measurements will be undermined without considering microtexture. This paper presents a study conducted to examine the use of laser-based sensors in measuring microtexture. The requirement of frequency was first established for choosing lasers for measuring pavement textures. Three variables, including the mean profile depth the slope variance and the root-mean-square were evaluated and utilized to characterize the microtexture profiles. These three variables varied with the baseline length and produced useful information for evaluating pavement friction. The correlation between surface friction and macrotexture and microtexture was also examined.
This paper reviews the requirements established by the Indiana Department of Transportation for the properties of aggregate materials to avoid poor friction characteristics of the coarse aggregates and provide durable pavement friction performance. The focus is on the construction of the tables of the friction characteristics for the typical aggregates and the friction performance for the typical hot-mix asphalt (HMA) mixtures used in Indiana. Without traffic application, the aging of HMA materials may not cause enough changes in pavement friction. In order to better evaluate the friction characteristics of the aggregates, this paper introduces the decreasing rate of the British pendulum number, which provides more consistent evaluation of the friction durability. This paper divides the variations of pavement friction over time into three phases and shows the corresponding friction patterns. Open-graded friction course and stone mastic asphalt mix produce more consistent friction performance than SuperPave mix. For a certain mix, steel slag provides greater friction numbers than crushed gravel, crushed stone, and dolomite aggregates. For SuperPave 9.5-mm mix, crushed gravel provides more consistent friction properties than dolomite and crushed stone in the first year. However, they may become compatible with each other in friction properties later.
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