Distributing State Road Use Tax Funds to Counties, HR-386, 1996

Iowa's county road system serves many critical functions in a changing environment. Many counties with very different social, economic, and demographic circumstances do not have adequate resources to provide the desired level of service on their secondary road systems. How the state's Road Use Tax Fund (RUTF) is distributed among counties is therefore of great importance. This report presents the results of a year-long study of how to distribute RUTF resources among Iowa's 99 counties. The project was undertaken at the request of county engineers who wish to replace the current method of allocation with one that is more stable, comprehensible, and predictable. This report describes the current allocation method, examines how other states distribute road funds to counties, and discusses potential allocation factors that could be included in a revised procedure. The process undertaken to narrow the range of possible formulas and determine the one to recommend is summarized. Finally, the report presents the allocation formula recommended by the project advisory committee, along with how it would operate.

Identification of Laboratory Techniques to Optimize Superpave HMA Surface Friction Characteristics, TR-450, 2010

Wet pavement friction is known to be one of the most important roadway safety parameters. In this research, frictional properties of flexible (asphalt) pavements were investigated. As a part of this study, a laboratory device to polish asphalt specimens was refined and a procedure to evaluate mixture frictional properties was proposed. Following this procedure, 46 different Superpave mixtures, one stone matrix asphalt (SMA) mixture and one porous friction course (PFC) mixture were tested. In addition, 23 different asphalt and two concrete field sections were also tested for friction and noise. The results of both field and laboratory measurements were used to develop an International Friction Index (IFI)-based protocol for measurement of the frictional characteristics of asphalt pavements for laboratory friction measurements. Based on the results of the study, it appears the content of high friction aggregate should be 20% or more of the total aggregate blend when used with other, polish susceptible coarse aggregates; the frictional properties increased substantially as the friction aggregate content increased above 20%. Both steel slag and quartzite were found to improve the frictional properties of the blend, though steel slag had a lower polishing rate. In general, mixes containing soft limestone demonstrated lower friction values than comparable mixes with hard limestone or dolomite. Larger nominal maximum aggregate size mixes had better overall frictional performance than smaller sized mixes. In addition, mixes with higher fineness moduli generally had higher macrotexture and friction.