Driveways are private roads that provide access (both ingress and egress) between a public way and abutting properties, and any facilities on those properties. The roadway engineers’ focus is often on a part of the driveway, the area where the driveway intersects the public highway or street. Since these connections form the link or interface between public streets and highways and the activities they serve, driveways are an integral part of the roadway transportation system. There has been relatively little comprehensive research on or national guidance for the geometric design of driveways in recent decades. The objective of this project was to develop recommendations for geometric design of driveways that will be useful to state departments of transportation, local governments, and consultants in preparing driveway design standards and practices. The project included an extensive review of related literature, a survey of transportation agencies, a listing of almost 100 factors that can affect the design of a driveway, a list of needed research topics, and research on issues related to driveway vertical alignment. The project produced two documents, the project report and a driveway design guide.
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This research provides a methodology for evaluation of durability related strength loss of bonded carbon fiber reinforced polymer (CFRP) systems applied to concrete beams. The report addresses test methods to establish a durability strength reduction factor, identification of corresponding field exposure conditions affecting durability, and suggestions for the application of the durability strength reduction factor for design of field applications. The durability strength reduction factor is a measure of the loss in strength over time due to environmental exposure. It is defined as the ratio of the flexural strength of a 4 in. x 4 in. x 14 in. concrete beam reinforced with CFRP exposed at 140°F and submerged in water or 100% relative humidity for 60 days to the flexural strength of a control specimen. The resulting durability strength reduction factor may be used to evaluate CFRP system performance. Two field environments are suggested: Wet and Air. In a Wet environment water accumulates at the bond surface. This is the default condition and corresponds to test results in submerged water at 140°F for 60 days. An Air environment allows drying between wetting episodes so water cannot accumulate on the bond surface. This condition corresponds to test results in 100% relative humidity at 140°F for 60 days.
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The objective of the first two phases of NCHRP Project 3-70 was to develop and test a framework and enhanced methods for determining levels of service for automobile, transit, bicycle, and pedestrian modes on urban streets, in particular with respect to the interaction among the modes. Phase 2 resulted in the multimodal level of service method (MMLOS) described in NCHRP Report 616, "Multimodal Level of Service for Urban Streets." The objective of Phase 3 of NCHRP Project 3-70 was to field test the MMLOS method with various public agencies around the United States. This Final Report presents the results of this third phase of the research. During Phase 3 the MMLOS method was field tested in 10 metropolitan areas of the United States. Public agency staffs were trained on the MMLOS method and it’s implementing software. They assisted in data collection and evaluated the suitability of the MMLOS method for use within their agency. Based on the results of these field tests several revisions were made to the spreadsheet software for implementing MMLOS. Additional guidance was provided to deal with conditions encountered in the field that were not anticipated when the original guide, NCHRP Web-Only Document 128, was written. Finally, a few minor modifications to the pedestrian level of service model are recommended to improve its sensitivity to some of the conditions encountered in the field tests.
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The research focused on: 1) Finalizing the two primary model components [i.e., a viscoelastic continuum damage (VECD) model for crack initiation and a hot mix asphalt fracture mechanics (HMA-FM) model for crack propagation], involving development and integration of sub-models that are relevant to dominant top-down cracking mechanisms into each model component; 2) Verifying the reasonableness of the two enhanced primary model components (i.e., the VECD-based model and the HMA-FM-based model); and 3) Developing for and integrating with the HMA-FM-based crack propagation model a simplified fracture energy-based crack initiation model to illustrate the potential of a completed system and to help formulate a plan for integrating, calibrating, and validating the two enhanced primary model components. In summary, the work performed clearly indicates that the VECD-based model and the HMA-FM-based model developed and evaluated in this project can form the basis for a top-down cracking model suitable for use in the Mechanistic-Empirical Pavement Design Guide (MEPDG). Furthermore, the component models can form the basis for an improved performance model to predict multiple cracking distresses simultaneously, including top-down cracking, bottom-up cracking, and thermal cracking. The project also identified and recommended research efforts to develop calibrated/validated top-down cracking performance models for use in the MEPDG.
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This report presents the results of an interlaboratory study (ILS) to prepare precision estimates for AASHTO T265 test method used for Laboratory Determination of Moisture Content of Soils. The materials for the ILS included two coarse- and two fine-grained soil-aggregate blends that were prepared according to Grading A and Grading E of AASHTO M147, “Materials for Aggregate and Soil-Aggregate Subbase, Base, and Surface Courses.” Each of the four blends had less than 10% soil passing #200 sieve to represent suitable materials for base and subbase. The comparison of the statistics of moisture content data for the four soil-aggregate blends indicated that the variability of moisture content measurement is the same for the blends with clay and silt; however, the variability is different for the blends with fine and coarse gradations. A precision statement for AASHTO T265 that includes the precision estimates developed in this study has been prepared and provided in the report.
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This report presents the results of an interlaboratory study (ILS) to prepare precision estimates for AASHTO T265 test method used for Laboratory Determination of Moisture Content of Soils. The materials for the ILS included two coarse- and two fine-grained soil-aggregate blends that were prepared according to Grading A and Grading E of AASHTO M147, “Materials for Aggregate and Soil-Aggregate Subbase, Base, and Surface Courses.” Each of the four blends had less than 10% soil passing #200 sieve to represent suitable materials for base and subbase. The comparison of the statistics of moisture content data for the four soil-aggregate blends indicated that the variability of moisture content measurement is the same for the blends with clay and silt; however, the variability is different for the blends with fine and coarse gradations. A precision statement for AASHTO T265 that includes the precision estimates developed in this study has been prepared and provided in the report.
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This report presents the results of a round robin study to prepare precision estimates for AASHTO T148 test method used for determining the length of a core drilled from a concrete pavement or structural element. The materials for the round robin included six concrete cores taken from LTPP test sections of FHWA. The cores were either 4” or 6” in diameter with varying length in the range of 4” to 12”. The cores were representative of different FHWA LTPP concrete pavement test sections from which they were removed. The apparatus for measuring the length of the cores was a 3-point callipering device specified in AASHTO T148 test method. The six specimens were carried around to eleven laboratories and the length measurements were collected. The results indicated that the repeatability and reproducibility precisions are significantly different for different core diameters. Therefore, the precision estimates were prepared separately for 4” and 6” diameter specimens.
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Determining Guidelines for Ramp and Interchange Spacing
Author: Ray, Brian L Kittelson and Associates, Incorporated Schoen, James Kittelson and Associates, Incorporated Jenior, Pete Kittelson and Associates, Incorporated Knudsen, Julia Kittelson and Associates, Incorporated Porter, Richard J University of Utah, Salt Lake City Leisch, Joel P Mason, John Roess, Roger | Size: 5.70 MB | Format:PDF | Quality:Original preprint | Publisher: Transportation Research Board | Year: 2010 | pages: 238 | ISBN: -
This project considered the effects of geometry, traffic operations, safety, signing, and other factors to develop guidelines for understanding the considerations that influence minimum ramp and interchange spacing values. Phase I included conducting a literature search and other information gathering activities, developing a work plan to assess the impact of ramp spacing on traffic operations and safety, and developing a framework for the research guidelines. Phase II included creating microscopic simulation models of closely-spaced ramp combinations calibrated with field data, constructing a crash database and developing crash prediction models, developing a set of guidelines for ramp and interchange spacing, and recommending changes to major resource documents within the transportation profession. As a final product, the team wrote NCHRP Report 687, "Guidelines for Ramp and Interchange Spacing," to assist users as they consider new or modified ramps and interchanges.
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Adapting Specification Criteria for Simple Performance Tests to HMA Mix Design
Author: Witczak, M W Arizona State University, Tempe El-Basyouny, M Arizona State University, Tempe Uzan, J Arizona State University, Tempe | Size: 1.99 MB | Format:PDF | Quality:Original preprint | Publisher: Transportation Research Board | Year: 2011 | pages: 64 | ISBN: -
The objective of this project was to develop a software program for evaluating the potential performance of hot mix asphalt (HMA) mix designs in combination with their intended pavement structures. This "Program for Integrated Analysis of HMA Mix And Structural Designs" is coded as a Microsoft Excel spreadsheet (9-33A(Sep10).xlsm) and supporting files. The program incorporates the Mechanistic-Empirical Pavement Design Guide (MEPDG) spreadsheet solutions developed in NCHRP Projects 9-19 and 9-22. Predictions of permanent deformation (rutting) and fatigue cracking are made on the basis of the estimated HMA dynamic modulus, E*; thermal cracking predictions are based on estimates of the HMA creep compliance, D. The program will serve as a multi-purpose tool for HMA mix and structural design engineers. First, it provides an easy graphical check that a prospective job mix formula (JMF) falls within the acceptable limits of air voids and effective binder volume established by the project’s HMA specification. Second, using powerful, pre-solved solutions of the MEPDG, it provides rapid estimates of the performance of the JMF over the design life of the HMA pavement and whether the JMF will satisfy specific pavement distress criteria established by the agency. Third, it can test “what-if” scenarios by estimating how changes in the JMF, pavement structure, or both may affect performance. Finally, it can be used in forensic investigations of pavement distresses, by assessing the potential contributions of the HMA and pavement structure to distress development before any testing is conducted. This report presents (1) a description of the program’s inputs and outputs, (2) a brief review of the underlying performance prediction models, and (3) examples illustrating the use of the program to analyze specific mix-structure combinations. Technical familiarity with the MEPDG design principles, the E* Simple Performance Test (SPT) Specification Criteria Program, and the Quality-Related Specification Software (QRSS) will enhance the user’s understanding of the program.
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