Signing on Very Low Volume Rurd Roads Iowa DOT Project HR-262, July, 1984

Research was undertaken to define an appropriate level of use of traffic control devices on rural secondary roads that carry very low traffic volumes. The goal of this research was to improve the safety and efficiency of travel on the rural secondary road system. This goal was to be accomplished by providing County Engineers with guidance concerning the cost-effective use of traffic control devices on very low volume rural roads. A further objective was to define the range of traffic volumes on the roads for which the recommendations would be appropriate. Little previous research has been directed toward roads that carry very low traffic volumes. Consequently, the factual input for this research was developed by conducting an inventory of the signs and markings actually in use on 2,069 miles of rural road in Iowa. Most of these roads carried 15 or fewer vehicles per day. Additional input was provided by a survey of the opinions of County Engineers and Supervisors in Iowa. Data from both the inventory and the opinion survey indicated a considerable lack of uniformity in the application of signs on very low volume rural roads. The number of warning signs installed varied from 0.24 per mile to 3.85 per mile in the 21 counties in which the inventory was carried out. The use of specific signs not only varied quite widely among counties but also indicated a lack of uniform application within counties. County officials generally favored varying the elaborateness of signing depending upon the type of surface and the volume of traffic on different roads. Less elaborate signing would be installed on an unpaved road than on a paved road. A concensus opinion was that roads carrying fewer than 25 vehicles per day should have fewer signs than roads carrying higher volumes. Although roads carrying 0 to 24 vehicles per day constituted over 24% of the total rural secondary system, they carried less than 3% of the total travel on that system. Virtually all of these roads are classified as area service roads and would thus be expected to carry only short trips primarily by local motorists. Consequently, it was concluded that the need for warning signs rarely can be demonstrated on unpaved rural roads with traffic volumes of fewer than 25 vehicles per day. It is recommended that each county designate a portion of its roads as an Area Service Level B system. All road segments with very low traffic volumes should be considered for inclusion in this system. Roads included in this system may receive a lesser level of maintenance and a reduced level of signing. The county is also afforded protection from liability arising from accidents occurring on roads designated as part of an Area Service Level B system. A uniform absence of warning signs on roads of this nature is not expected to have any discernible effect on the safety or quality of service on these very low volume roads. The resources conserved may be expended more effectively to upgrade maintenance and traffic control on roads carrying higher volumes where the beneficial effect on highway safety and service will be much more consequential.

A Comparison of Mobile Scanning to a Total Station Survey at the I-35 and IA 92 Interchange in Warren County, Iowa, August 15, 2012

The purpose of this project was to investigate the potential for collecting and using data from mobile terrestrial laser scanning (MTLS) technology that would reduce the need for traditional survey methods for the development of highway improvement projects at the Iowa Department of Transportation (Iowa DOT). The primary interest in investigating mobile scanning technology is to minimize the exposure of field surveyors to dangerous high volume traffic situations. Issues investigated were cost, timeframe, accuracy, contracting specifications, data capture extents, data extraction capabilities and data storage issues associated with mobile scanning. The project area selected for evaluation was the I-35/IA 92 interchange in Warren County, Iowa. This project covers approximately one mile of I-35, one mile of IA 92, 4 interchange ramps, and bridges within these limits. Delivered LAS and image files for this project totaled almost 31GB. There is nearly a 6-fold increase in the size of the scan data after post-processing. Camera data, when enabled, produced approximately 900MB of imagery data per mile using a 2- camera, 5 megapixel system. A comparison was done between 1823 points on the pavement that were surveyed by Iowa DOT staff using a total station and the same points generated through the MTLS process. The data acquired through the MTLS and data processing met the Iowa DOT specifications for engineering survey. A list of benefits and challenges is included in the detailed report. With the success of this project, it is anticipate[d] that additional projects will be scanned for the Iowa DOT for use in the development of highway improvement projects.

Evaluation of Mitigation for Safety Concerns on Low-Volume, Unpaved Rural Roads, 2013.

The Institute for Transportation (InTrans) at Iowa State University completed work on an in-depth study of crash history on lowvolume, rural roads in Iowa in December 2010. Results indicated that unpaved roads with traffic volumes greater than 100 vehicles per day (vpd) exhibit significantly higher crash frequencies, rates, and densities than any other class of low-volume road examined, paved or unpaved. The total mileage for this class of roadway in Iowa is only about 4,400 miles, spread over 99 counties in the state, which is certainly a manageable number of miles for individual rural agencies. The purpose of this study was to identify and examine several unpaved, local road segments with higher than average crash frequencies, select and undertake potentially-beneficial mitigation, and evaluate the results as time allowed. A variety of low-cost options were considered, including engineering improvements, enhanced efforts by law enforcement, and educational initiatives. Using input, active support, and participation from local agencies and state and Federal safety advocates, the study afforded a unique opportunity to examine useful tools for local rural agencies to utilize in addressing safety on this particular type of roadway.

Evaluation of Mitigation for Safety Concerns on Low-Volume, Unpaved Rural Roads: Tech Transfer Summary, 2013.

The Institute for Transportation (InTrans) at Iowa State University completed work on an in-depth study of crash history on lowvolume, rural roads in Iowa in December 2010. Results indicated that unpaved roads with traffic volumes greater than 100 vehicles per day (vpd) exhibit significantly higher crash frequencies, rates, and densities than any other class of low-volume road examined, paved or unpaved. The total mileage for this class of roadway in Iowa is only about 4,400 miles, spread over 99 counties in the state, which is certainly a manageable number of miles for individual rural agencies. The purpose of this study was to identify and examine several unpaved, local road segments with higher than average crash frequencies, select and undertake potentially-beneficial mitigation, and evaluate the results as time allowed. A variety of low-cost options were considered, including engineering improvements, enhanced efforts by law enforcement, and educational initiatives. Using input, active support, and participation from local agencies and state and Federal safety advocates, the study afforded a unique opportunity to examine useful tools for local rural agencies to utilize in addressing safety on this particular type of roadway.

Investigation of Two Bridge Alternatives for Low Volume Roads Volume 2 of 2 Concept 2: Beam In Slab Bridge, HR-382, 1997

Recent reports have indicated that 23.5% of the nation's highway bridges are structurally deficient and 17.7% are functionally obsolete. A significant number of these bridges are on the Iowa secondary road system where over 86% of the rural bridge management responsibilities are assigned to the counties. Some of the bridges can be strengthened or otherwise rehabilitated, but many more are in need of immediate replacement. In a recent investigation (HR-365 "Evaluation of Bridge Replacement Alternatives for the County Bridge System") several types of replacement bridges that are currently being used on low volume roads were identified. It was also determined that a large number of counties (69%) have the ability and are interested in utilizing their own forces to design and construct short span bridges. After reviewing the results from HR-365, the research team developed one "new" bridge replacement concept and a modification of a replacement system currently being used. Both of these bridge replacement alternatives were investigated in this study, the results of which are presented in two volumes. This volume (Volume 2) presents the results of Concept 2 - Modification of the Beam-in-Slab Bridge. Concept 1 - Steel Beam Precast Units is presented in Volume 1. Concept 2 involves various laboratory tests of the Beam-in-Slab bridge (BISB) currently being used by Benton County and several other Iowa counties. In this investigation, the behavior and strength of the BISB were determined; a new method of obtaining composite action between the steel beams and concrete was also tested. Since the Concept 2 bridge is primarily intended for use on low-volume roads, the system can be constructed with new or used beams. In the experimental part of the investigation, there were three types of laboratory tests: push-out tests, service and ultimate load tests of models of the BISB, and composite beam tests utilizing the newly developed shear connection. In addition to the laboratory tests, there was a field test in which an existing BISB was service load tested. An equation was developed for predicting the strength of the shear connection investigated; in addition, a finite element model for analyzing the BISB was also developed. Push-out tests were completed to determine the strength of the recently developed shear connector. A total of 36 specimens were tested, with variables such as hole diameter, hole spacing, presence of reinforcement, etc. being investigated. In the model tests of the BISB, two and four beam specimens [L=9,140 mm (30 ft)] were service load tested for behavior and load distribution data. Upon completion of these tests, both specimens were loaded to failure. In the composite beam tests, four beams, one with standard shear studs and three using the shear connection developed, were tested. Upon completion of the service load tests, all four beams were loaded to failure. The strength and behavior of the beams with the new shear connection were found to be essentially the same as that of the specimen with standard shear studs.

Evaluation of Gap-Graded Asphalt Concrete Mixtures, Vol. 1. Physical Properties (Part I: Mechanical Properties), HR-157, Volume 1, 1972 (1973)

This report presents the results of a comparative laboratory study between well- and gap-graded aggregates used in asphalt concrete paving mixtures. A total of 424 batches of asphalt concrete mixtures and 3,960 Marshall and Hveem specimens were examined. There is strong evidence from this investigation that, with proper-combinations of aggregates and asphalts, both continuous- and gap-graded aggregates can produce mixtures of high density and of qualities meeting current design criteria. There is also reason to believe that the unqualified acceptance of some supposedly desirable, constant, mathematical relationship between adjacent particle sizes of the form such as Fuller's curve p = 100(d/D)^n is not justified. It is recommended that the aggregate grading limits be relaxed or eliminated and that the acceptance or rejection of an aggregate for use in asphalt pavement be based on individual mixture evaluation. Furthermore, because of the potential attractiveness of gap-graded asphalt concrete in cost, quality, and skid and wear resistance, selected gap-graded mixtures are recommended for further tests both in the laboratory and in the field, especially in regard to ease of compaction and skid and wear resistance.

Evaluation of Gap-Graded Asphalt Concrete Mixtures Vol. 3. Appendix, HR-157, Volume 3 (Part 3), 1972 (1973)

This report presents the results of a comparative laboratory study between well- and gap-graded aggregates used in asphalt concrete paving mixtures. A total of 424 batches of asphalt concrete mixtures and 3,960 Marshall and Hveem specimens were examined. There is strong evidence from this investigation that, with proper combinations of aggregates and asphalts, both continuous- and gap-graded aggregates can produce mixtures of high density and of qualities meeting current design criteria. There is also reason to believe that the unqualified acceptance of some supposedly desirable, constant, mathematical relationship between adjacent particle sizes of the form such as Fuller's curve p = 100 (d/D)n is not justified. It is recommended that. the aggregate grading limits be relaxed or eliminated and that the acceptance or rejection of an aggregate for use in asphalt pavement be based on individual mixture evaluation. Furthermore, because of the potential attractiveness of gap-graded asphalt concrete in cost, quality, and skid and wear resistance, selected gap-graded mixtures are recommended for further tests both in the laboratory and in the field, especially in regard to ease of compaction and skid and wear resistance.

Field Testing of Railroad Flatcar Bridges Volume I: Single Spans, TR-498, 2007

Based on the conclusions of IHRB Project TR-444, Demonstration Project Using Railroad Flat Car Bridges for Low Volume Road Bridges, additional research on the use of RRFC bridges was undertaken. This portion of the project investigated the following: (1) Different design and rating procedures; (2) Additional single span configurations plus multiple span configurations; (3) Different mechanisms for connecting adjacent RRFCs and the resulting lateral load distribution factors; (4) Sheet pile abutments; and (5) Behavior RRFCs that had been strengthened so that they could be used on existing abutments. A total of eight RRFC bridges were tested (five single span bridges, two two-span bridges, and one three-span bridge). Based on the results of this study a simplified design and rating procedure has been developed for the economical replacement bridge alternative. In Volume 1, this volume, the results from the testing of four single span RRFC bridges are presented, while in Volume 2 the results from the testing of the strengthened single span bridge plus the three multiple span bridges are presented.

Field Testing of Railroad Flatcar Bridges Volume II: Multiple Spans, TR-498, 2007

Based on the conclusions of IHRB Project TR-444, Demonstration Project Using Railroad Flat Car Bridges for Low Volume Road Bridges, additional research on the use of RRFC bridges was undertaken. This portion of the project investigated the following: (1) Different design and rating procedures; (2) Additional single span configurations plus multiple span configurations; (3) Different mechanisms for connecting adjacent RRFCs and the resulting lateral load distribution factors; (4) Sheet pile abutments; and (5) Behavior RRFCs that had been strengthened so that they could be used on existing abutments. A total of eight RRFC bridges were tested (five single span bridges, two two-span bridges, and one three-span bridge). Based on the results of this study a simplified design and rating procedure has been developed for the economical replacement bridge alternative. In Volume 1, the results from the testing of four single span RRFC bridges are presented, while in Volume 2,this volume, the results from the testing of the strengthened single span bridge plus the three multiple span bridges are presented.

Development of LRFD Procedures for Bridge Pile Foundations in Iowa Volume III: Recommended Resistance Factors with Consideration of Construction Control and Setup, TR-584, 2012

The Federal Highway Administration (FHWA) mandated utilizing the Load and Resistance Factor Design (LRFD) approach for all new bridges initiated in the United States after October 1, 2007. As a result, there has been a progressive move among state Departments of Transportation (DOTs) toward an increased use of the LRFD in geotechnical design practices. For the above reasons, the Iowa Highway Research Board (IHRB) sponsored three research projects: TR-573, TR-583 and TR-584. The research information is summarized in the project web site (http://srg.cce.iastate.edu/lrfd/). Two reports of total four volumes have been published. Report volume I by Roling et al. (2010) described the development of a user-friendly and electronic database (PILOT). Report volume II by Ng et al. (2011) summarized the 10 full-scale field tests conducted throughout Iowa and data analyses. This report presents the development of regionally calibrated LRFD resistance factors for bridge pile foundations in Iowa based on reliability theory, focusing on the strength limit states and incorporating the construction control aspects and soil setup into the design process. The calibration framework was selected to follow the guidelines provided by the American Association of State Highway and Transportation Officials (AASHTO), taking into consideration the current local practices. The resistance factors were developed for general and in-house static analysis methods used for the design of pile foundations as well as for dynamic analysis methods and dynamic formulas used for construction control. The following notable benefits to the bridge foundation design were attained in this project: 1) comprehensive design tables and charts were developed to facilitate the implementation of the LRFD approach, ensuring uniform reliability and consistency in the design and construction processes of bridge pile foundations; 2) the results showed a substantial gain in the factored capacity compared to the 2008 AASHTO-LRFD recommendations; and 3) contribution to the existing knowledge, thereby advancing the foundation design and construction practices in Iowa and the nation.