Federal Highway Administration

About: Federal Highway Administration is a government organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Poison control & Bridge (interpersonal). The organization has 574 authors who have published 950 publications receiving 17884 citations. The organization is also known as: FHWA.

Estimating safety by the empirical bayes method: a tutorial

Abstract: The empirical Bayes (EB) method addresses two problems of safety estimation: it increases the precision of estimates beyond what is possible when one is limited to the use of a 2- to 3-year accident history, and it corrects for the regression-to-mean bias. The increase in precision is important when the usual estimate is too imprecise to be useful. The elimination of the regression-to-mean bias is important whenever the accident history of the entity is in some way connected with the reason why its safety is estimated. The theory of the EB method is well developed. It is now used in the Interactive Highway Safety Design Model and will be used in the Comprehensive Highway Safety Improvement Model. The time has come for the EB method to be the standard and staple of professional practice. The study's goal is to facilitate the transition from theory into practice.

Accident models for two-lane rural segments and intersections

Abstract: Data collected from the states of Minnesota and Washington on rural two-lane highways are used to build accident models for segments and three-legged and four-legged intersections stop-controlled on the minor legs The quantity, quality, and variety of data collected, together with the advanced techniques applied in the analysis, make this study of special interest Variables include traffic, horizontal and vertical alignments, lane and shoulder widths, roadside hazard rating, channelization, and number of driveways Models are of negative binomial and extended negative binomial form and yield R2 values from 042 to 073 and overdispersion parameters from 020 to 051 A segment model combining both states and including state as a variable, and intersection models derived from Minnesota data, are featured, along with summary statistics, goodness-of-fit measures, and cross-validation between the states Segment accidents depend significantly on most of the roadway variables collected, while intersection ac

Characterization of air void distribution in asphalt mixes using x-ray computed tomography

Abstract: This study describes experimental and analytical methods to quantify the structure of air voids in asphalt mixes. An x-ray computed tomography system along with image analysis techniques were used to measure air void sizes at different depths within asphalt mix specimens. The statistical analyses performed validated the applicability of the Weibull model for describing the air void distribution. Consequently, the Weibull model was used to quantify the effect of the compaction effort, method of compaction, and aggregate size distribution on air voids. The air void size distribution in Superpave gyratory compacted specimens was found to exhibit a “bathtub” shape, whereby larger voids were present at the top and bottom parts of a specimen. This shape was more pronounced at higher compaction efforts. The method of compaction was significant in influencing the air void size distribution. Specimens prepared using the Superpave gyratory compactor with different aggregate sizes were found to have noticeably diffe...

The Relationship of the MSCR Test to Rutting

Abstract: The Multi-stress Creep and Recovery (MSCR) Test is currently being considered as a replacement for the Superpave high temperature binder criteria G* sinδ. The MSCR test can distinguish between the rutting properties of both neat binders and polymer modified binders. The test is run on the same dynamic shear rheometer test equipment currently used for the current Superpave binder testing and is easy to run. The validation of the MSCR compliance value Jnr to rutting was done through extensive mix testing using laboratory rut testers, large Accelerated Loading Facilities and actual roadway sections. This paper covers the validation of the MSCR test binder compliance value Jnr to mixture rutting for modified and neat binders. Multiple binders and mix types are included in the validation and it is demonstrated that the MSCR test provides a much better correlation to mixture rutting than the existing Superpave binder criteria.

Using Semi Circular Bending Test to Evaluate Low Temperature Fracture Resistance for Asphalt Concrete

Abstract: This work presents a repeatable semi circular bending (SCB) fracture test to evaluate the low temperature fracture resistance of asphalt mixture. The fracture resistance of six asphalt mixtures, which represent a combination of factors such as binder type, binder modifier, aggregate type, and air voids, and two testing conditions of loading rate and initial notch length, was evaluated by performing SCB fracture tests at three low temperatures. Fracture energy was calculated from the experimental data. Experimental results indicated strong dependence of the low temperature fracture resistance on the test temperature. Experimental plots and low coefficient of variation (COV) values from three replicates show a satisfactory repeatability from the test. The results of the analysis showed that fracture resistance of asphalt mixtures is significantly affected by type of aggregate and air void content. Experimental results also confirmed the significance of binder grade and modifier type with relation to cracking resistance of asphalt mixtures. Analysis of result also indicated that both the loading rate and initial notch length had significant effect on the fracture energy at the highest test temperature, whereas the effect was strongly diluted at the two lower temperatures. No clear trend was found with the fracture peak load from either the effect of loading rate or notch length.