Evaluation of Bias in the Hamburg Wheel Tracking Device, RB00-010, 2013

As the list of states adopting the HWTD continues to grow, there is a need to evaluate how results are utilized. AASHTO T 324 does not standardize the analysis and reporting of test results. Furthermore, processing and reporting of the results among manufacturers is not uniform. This is partly due to the variation among agency reporting requirements. Some include only the midpoint rut depth, while others include the average across the entire length of the wheel track. To eliminate bias in reporting, statistical analysis was performed on over 150 test runs on gyratory specimens. Measurement location was found to be a source of significant variation in the HWTD. This is likely due to the nonuniform wheel speed across the specimen, geometry of the specimen, and air void profile. Eliminating this source of bias when reporting results is feasible though is dependent upon the average rut depth at the final pass. When reporting rut depth at the final pass, it is suggested for poor performing samples to average measurement locations near the interface of the adjoining gyratory specimens. This is necessary due to the wheel lipping on the mold. For all other samples it is reasonable to only eliminate the 3 locations furthest from the gear house. For multi‐wheel units, wheel side was also found to be significant for poor and good performing samples. After eliminating the suggested measurements from the analysis, the wheel was no longer a significant source of variation.

Pieces of Iowa’s Past, January 23, 2013

Pieces of Iowa’s Past, published by the Iowa State Capitol Tour Guides weekly during the legislative session, features historical facts about Iowa, the Capitol, and the early workings of state government. All historical publications are reproduced here with the actual spelling, punctuation, and grammar retained. January 23, 2013 THIS WEEK: Iowa’s Grasshopper Plague of 1873 BACKGROUND: Fifteen General Assembly The 15th General Assembly convened January 12 and adjourned March 19, 1874—a 67-day session. The Senate had six Democratic members, 34 Republican members, and 10 Independent members. The House of Representatives had six Democratic members, 50 Republican members, and 44 Independent members. There were a total of 150 legislators in Iowa. By 1874, the Capital had been relocated to Des Moines. The legislature had occupied the old Brick Capitol since 1858. Joseph Dysart was the Lieutenant Governor presiding in the Senate, and John Gear was Speaker of the House of Representatives. Iowa’s population at the 1870 federal census had grown to 1,194,020. Both House and Senate journals from the 15th Iowa General Assembly include several references to assisting the destitution brought on by the 1874 plague of grasshoppers in Northwestern Iowa. Senator Perkins, from the Special Committee appointed to inquire into the reports of destitution in the northwestern counties of Iowa, submitted the following report, in part: “We have examined such evidence as is attainable here, and made such inquiries of parties interested in affording temporary relief as were to be met, and are pieces satisfied in our own minds that the case is one of sufficient importance to command the attention of the State.”