Institute for Transportation

About the research

The project described in the report was developed in response to a documented need for more readily available guidance related to decision-making about roadway cross section reconfigurations. More specifically, there was a need for information that might help during the decision-making process involved in converting four-lane undivided roadway cross sections to three lanes (four- to three-lane conversion) with one through lane in each direction and a two-way left-turn lane.

In response to this need, this project, through consultation with practitioners, identified and developed summary responses to 14 commonly asked questions related to the planning, design, operation, and/or implementation of four- to three-lane conversions. Some of the responses to these questions may also be relevant to the process implemented for other types of conversions and roadway improvements. The summary responses to the questions identified were purposefully kept short and are contained in Appendix A of the report as well as separate standalone documents. References for each summary response, if needed by the user of this guidance, are provided in Appendix B of the report.

Conclusions and recommendations are summarized in the report based on the tasks completed as part of this project. The conclusions are related to the amount and relevancy of material available on four- to three-lane conversions and how the approach to roadway design and operational analysis is changing overall. Recommendations are made about the potential to answer more questions as they are identified, the development of materials specifically for elected officials, and a possible update of the Iowa guidelines for four- to three-lane conversions as an addendum to the national guidelines.

About the research

Live load field tests of bridges were carried out using certain implements of husbandry (IoH) to observe the transverse load distribution and the dynamic impacts. A finite element (FE) analysis of the field-tested bridges was performed. The strain data from the FE analysis were validated with the field test data to establish an FE analysis method for a parametric study. This parametric study was performed to observe the influence of various bridge parameters on the load distribution factors. Observation of the load distribution factors from the parametric study shows that the load distribution factor equations prescribed in the AASHTO LRFD (2020) capture the distribution for these IoH loads. Live load factors for this load type for prestressed concrete (PC) bridges and steel girder bridges were found through a calibration process using reliability theory, which involves the selection of a target safety index. The live load factor for each bridge type was calculated for the Strength I and II limit states. An Iowa-specific legally loaded vehicle (Terragator Max) was established using a conservative axle configuration and axle loads of 25 kips. Calibration of the live load factors yielded the following key findings:

• An update to the AASHTO load and resistance factors (LRFs) is not needed for existing terragator loads as long as the axle loads comply with the legal load limit of 25 kips.
• When a target safety index of 3.5 is considered, the current live load factor of 1.75 for Strength I should be increased to 1.90 if husbandry vehicles of a configuration similar to that of Terragator Max are manufactured.
• When a target safety index of 2.0 is considered, the same case does not suggest an update to the AASHTO live load factor.
• An update to the AASHTO Strength II LRFs is not required.
• The dead load factors were found to be lower than the current AASHTO-prescribed values. Therefore an update to the AASHTO LRFs is not required.

About the research

The design of drilled shafts in Iowa currently relies on the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications. To improve design efficiency at the state level, a series of research projects was conducted to develop the Drilled SHAft Foundation Testing (DSHAFT) database, a regional database facilitating the collection, storage, and efficient access of load test data from Iowa and other states, and to utilize the collected data to establish regional resistance factors that are reflective of the uncertainties associated with predicting drilled shaft capacity under Iowa’s specific geological conditions and construction practices. Resistance factors established in a 2019 study for various resistance prediction methods generally showed improvements over those recommended by AASHTO.

The present research aimed to validate the proposed resistance factors and formulate design recommendations for implementation. To this end, the DSHAFT database was further expanded with additional test data. Additionally, regression analyses were conducted on test data from Iowa to develop local resistance predictions that may provide more accurate estimates of drilled shaft capacity locally. Results from the analysis indicated that a linear correlation between soil parameters and measured unit side resistance was the best fit for most soil types. Moreover, settlement data were collected at several production shafts that were part of a few Iowa DOT bridge replacement projects to evaluate the field performance of drilled shafts designed under the current Iowa DOT guidelines. Various challenges were encountered during the data collection process. Some of the data indicated unexpected negative settlements, and further investigation is needed to develop appropriate conclusions. Design recommendations were formulated based on all findings, and design examples were developed to illustrate the application of the design recommendations.

About the research

The Iowa Work Zone Safety Workshops have provided an opportunity for operations personnel from various cities in Iowa to improve their work zone safety and setups when conducting routine street maintenance. Many participants come from cities with a population of less than 10,000 residents and small city budgets for this type of work can sometimes lead to a lack of funding for temporary traffic control devices and the use of signs, barricades, cones, and vests that are deteriorated and may be out of compliance with the 2009 Manual on Uniform Traffic Control Devices (MUTCD).

This project was developed to assist smaller cities with the introduction or upgrade of their temporary traffic control devices and vests to meet current standards for compliance and to make their work zones safer for workers and motorists. The program has grown from 10 applications in 2017, the initial year of the project, to over 100 in 2022–2023, and nearly 200 in 2023–2024.

The goal of this project is to provide an avenue for smaller cities to be able to obtain a basic work zone sign package that is in compliance with the 2009 MUTCD and to make their work zones safer for operations personnel and motorists. It is currently proposed that the materials to be included in the package will be the following:

• One Lane Road Ahead Signs
• Road Work Ahead Signs with “CLOSED” snap on
• Be Prepared to Stop Signs
• Type III Barricades
• 28” Traffic Cones
• Class 2 Safety Vests
• Sign Stands
• 42 inch Channelizers

About the research

A Performance Centered Concrete Construction initiative will assure that any new concrete pavement or overlay will last for the intended period, with a minimum of distress, at a low life-cycle cost in an increasingly sustainable way. Reducing the need to replace or repair any concrete pavement will provide the direct benefits of saving money, decreasing CO2 footprint, and easing traffic delays – all of which are beneficial to sustainability. Fewer closures over the life of the pavement also enhances the safety of the traveling public and road workers.

About the research

Roads pose several risks to wildlife due to several sources, including direct mortality from vehicle collisions, fragmentation of key habitat, and creating barriers to movement that result in isolated populations. For imperiled species, such threats can have an outsize impact on species persistence. Mitigation efforts such as wildlife crossings, fencing, roadside vegetation management, and retrofitting roads with wildlife-friendly design features have been shown to be effective at reducing the negative impacts of roads on wildlife.

This project seeks to identify priority sites in Iowa where road mitigation can provide the largest benefit to Species of Greatest Conservation Need (SGCN). The research will build upon ongoing work developing habitat suitability models for a suite of SGCN to predict statewide species’ occurrence under both current conditions and predicted future climate and land use change to develop a gridded biodiversity index. The research will use geospatial data on road configuration, traffic intensity, and wildlife mortalities to quantify road risk to identify sites with the highest combined biodiversity scores and road risk. Field surveys at these sites will be conducted in order to ground-truth model predictions, provide empirical estimates of species richness and density, and evaluate the feasibility and expected benefits of different mitigation efforts. Project deliverables include: (1) recommendations for road mitigations at 10 sites identified to be SGCN hotspots, (2) geospatial data layers of current and future predicted SGCN occurrence and road risk to prioritize future sites for mitigation, and (3) a proposed monitoring plan for evaluating mitigation measures post-implementation.

This project will help the Iowa DOT reduce negative impacts of roads, support conservation of Iowa’s wildlife, and provide a framework for prioritizing mitigation efforts that can serve as a model for other states in the Midwest.

About the research

The objective of this project is to conduct an independent evaluation of the impact of biodiesel on fuel economy and carbon reduction in the Iowa DOT snowplow fleet. This includes an evaluation of fuel economy, maintenance, and driver/maintenance personnel concerns.

The team will coordinate with the Iowa DOT and monitor snowplow operations. Fuel use and snowplow maintenance using varying levels of both biodiesel and regular diesel will be monitored.

The following tasks will be carried out in the Phase II research:

• Track fuel economy and maintenance through maintenance records for 2023/2024 winter season
• Summarize fuel economy and maintenance impacts overall
• Survey operators to identify barriers to adoption
• Develop tool for agencies to estimate fuel savings, carbon reduction, and costs when considering the use of biodiesel in snowplows and maintenance equipment
• Provide recommendations to overcome barriers to adoption
• Outreach and implementation activities such as a workshop for local agencies

About the research

The objectives of this study are as follows: (1) Provide communication and information sharing among member states. Discuss research needs and provide research ideas to be developed through TRB (and other research opportunities). (2) Provide a technology and knowledge exchange forum to enhance the practical knowledge of member states concerning asset management implementation. (3) Enhance the working knowledge of the asset management community.

About the research

The goal of this project is to study the effectiveness of stabilization of granular-surfaced (“gravel”) roads using wicking and non-wicking geosynthetics. The project will continue a newly established cooperative partnership with the Iowa Army National Guard that enables long-term research on granular-surfaced roads at the Camp Dodge base in Johnston, Iowa. The Camp Dodge facility contains several miles of granular-surfaced roads that routinely exhibit various types of damage and distress including rutting, potholes, washboarding, frost boils, insufficient drainage, and other moisture related damage.

About the research

Superheavy loading vehicles, commonly referred to as superloads, exhibit non-standardized loading configurations along with high gross vehicle weights and axle loadings, all of which may cause unexpected distresses on Iowa road infrastructure systems compared to those caused by conventional vehicle class types categorized by the Federal Highway Administration. Superloads encompass various types of vehicles, including implements of husbandry and superheavy loads, prevalent in the Midwestern region of the United States. The determination of critical load factors affecting road damage due to superloads is intricate due to their non-standardized loading configurations and high loading capacities.

This study developed methodologies to quantify superloads and evaluate their impact on Iowa’s road infrastructure, encompassing jointed plain concrete pavements, flexible pavements, and granular roads. It employed extensive mechanistic-based numerical analysis, life-cycle cost analysis, artificial intelligence (AI)-based predictive modeling, forensic investigations, field data analysis, and prototype tool development, with the research aimed at comprehensively evaluating superload impacts on various road types and structures.

Through extensive numerical analyses, incorporating both mechanistic and empirical methodologies, critical findings regarding the effects of different superload types on pavement and granular road distress, associated treatment cost, and service life reduction emerged. Moreover, the Road Infrastructure-Superload Analysis Tool (RISAT) developed in this study has the potential to provide a user-friendly platform for engineers and planners to evaluate structural damages and associated treatment costs induced by superload traffic. The integration of AI-based predictive models into the RISAT enables users to input pavement and superload properties to obtain highly accurate predictions of pavement damages, treatment costs, and service life reductions. Incorporating field data into the RISAT also enhanced its reliability and applicability to pavement management practices, providing engineers and planners with valuable insights for informed decision-making regarding pavement design, maintenance, and rehabilitation strategies.