Institute for Transportation

About the research

The overall goal of this project is to understand the impact of using geocells in granular-surfaced road construction in terms of field performance assessed through measurements of rutting, breakage, stiffness, and strength profiles, as well as resilient properties measured in a large scale laboratory test device with cycling loading. The overall workplan includes construction of field test sections, performance of in-situ tests and sampling through two winter-spring seasons, and laboratory investigations to quantify both the short-term and long-term benefits of geocells to help develop construction guidelines and specifications.

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 more than 150 in 2024–2025.

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

More information on the program can be found on the Iowa LTAP Work Zone Sign Package Program page.

About the research

Inclusion of randomly-oriented, discrete fibers in cementitious materials is proven to enhance many of the desired engineering properties, such as fracture toughness, flexural strength, and resistance to the formation and propagation of micro/macro cracks under extreme loads, in addition to reducing the risk of early-age cracks in concrete. The concrete fibers can be broadly categorized to metallic and non-metallic fibers. Among their differences, non-metallic fibers offer high corrosion resistance, in contrast to metallic fibers, which are vulnerable to corrosion, despite offering superior mechanical properties.

This project aims to conduct a holistic investigation of a hybrid of metallic and non-metallic fibers to introduce expected functionalities to fiber-reinforced cementitious materials, especially ultra-high performance concrete (UHPC). Use of alternative fibers for non-structural UHPC applications will particularly reduce costs and eliminate the need for Buy America as required with steel fibers. Considering the latest fiber products available in the market, this project will investigate the promise of a new generation of UHPC mixtures engineered by appropriate choices and dosages of fibers. Based on a suite of laboratory investigations, the ultimate goal of this project will be to develop practical guidelines to select a hybrid of metallic and non-metallic fibers for non-structural UHPC. The fiber selection criteria will be consistent with target applications, providing the desired mechanical and durability properties, paired with high corrosion resistance and adequate bond with the cementitious matrix.

About the research

Between 2016 and 2020, nearly 2,900 fatal, serious injury, and minor injury crashes occurred in Iowa at paved, all-way stop control and partial stop control intersections with at least one approach having a speed limit exceeding 45 mph, i.e., high-speed intersections. This increases to nearly 7,800 fatal, serious injury, and minor injury crashes when considering all paved, unsignalized intersections in the state. At the national level, 18% of all fatal crashes occurred at unsignalized intersections in 2018.

Several factors can contribute to crashes at unsignalized intersections, including drivers failing to recognize the intersection, not complying with the traffic control, or selecting inappropriate gaps. Additionally, reaction times are reduced as speeds increase, and the severity of crashes is greater. In fact, the safe system speed for “car/car (side impact, intersections)” crashes is only approximately 30 mph. Traffic signal installation is a countermeasure that may be considered at high-speed intersections; however, national research presents mixed findings on its effectiveness.

Since Iowa has a robust intersection database, high-quality crash data, and prior experience developing intersection safety performance functions (SPFs), this research focused on creating Iowa-specific crash modification factors (CMFs) for signalizing high-speed intersections. A five-step methodology was implemented.

This research revealed that signal installations at non-ramp high-speed locations increase all but broadside crashes on most facility types. The findings showed that signal installation at high-speed intersections reduced broadside crashes by less than 64%, while rear-end crashes increased by more than 70%, depending on intersection geometric characteristics. Additional CMF values were derived for subsets of high-speed intersection types, including divided, undivided, three-leg, and four-leg intersections. The report showcases a comparative analysis of the impact of signalization on different classes of high-speed intersections. The study’s results were validated through hypothesis tests of proportions analysis and comparisons with existing literature.

About the research

In 1999, the Center for Transportation Research and Education (CTRE) at Iowa State University’s (Iowa State’s) Institute for Transportation (InTrans) developed the book Iowa Highway Research Board: 1949–1999. The book summarized the history of highway research in Iowa, the germination of the Iowa Highway Research Board (IHRB), and highlights of the board’s research program in its first 50 years.

Given the technological, computational, and theoretical advances in transportation engineering over the past 25 years, along with a desire to highlight the board’s historical and current impacts, the IHRB was interested in continuing the narrative begun in Iowa Highway Research Board: 1949–1999 to cover the board’s history since 1999.

The objective of this project was to create a book that encompasses the IHRB’s history and funded projects from 2000 to 2024.

About the research

Pavement friction significantly contributes to roadway safety by providing the grip required for safe travel. The Iowa Department of Transportation (DOT) has long recognized the importance of evaluating pavement skid resistance and its impact on traffic safety.

Several devices have been developed to measure skid resistance. The Iowa DOT currently uses the locked-wheel skid tester (LWST), which is well accepted across the United States and globally. Due to its relatively narrow speed range and limitations on curves and short, low-speed segments, various types of continuous friction measurement equipment (CFME) have been proposed as alternatives, including the GripTester and sideway-force coefficient routine investigation machine (SCRIM). A broader issue in friction measurement is repeatability and reliability under different operational conditions, with temperature, pavement wetting, and test speed affecting the correlation between different devices.

This study aimed to evaluate candidate CFME technologies for their ability to measure pavement friction at different test speeds and in different operational conditions relative to the LWST currently available at the Iowa DOT. Promising CFME technologies were selected, and a testing program based on statistical procedures was designed to evaluate the devices’ suitability for pavement friction evaluation in relation to the friction demand and safety analysis. CFME and LWST testing was performed at three asphalt and three concrete pavement test segments at different speeds and using smooth and ribbed tires, and tests were repeated on different days to determine performance in different operational conditions. A dynamic friction tester (DFT) and laser texture scanner (LTS) were used to verify the correlation between the CFME and LWST and to investigate the impact of pavement texture on dry and wet skid resistance.

The research resulted in guidance and recommendations for friction evaluation on different components of the network, including curves and low-speed segments. These outcomes represent a step toward a consistent procedure for both routine pavement friction evaluation at the network level and spot investigation for high-risk areas.

About the research

The Federal Highway Administration has provided funding to the state Local Technical Assistance Programs (LTAPs) to assist, as they are able, in the provision of training and/or technical assistance in the area of construction project environmental reviews. The funds could be used for a variety of activities (to be defined in the LTAP application) that facilitate the environmental review process and build capacity to complete the reviews. Iowa LTAP, in collaboration with its partners, submitted an application that included the development and offering of a webinar, two National Highway Institute courses, an interactive form to help track activities, and a flipbook or brochure on mitigation measures connected to threatened and endangered species in Iowa.

About the research

The Iowa Department of Transportation (DOT) Modal Transportation Bureau Office of Public Transit requested a proposal from the Iowa Local Technical Assistance Program at the Institute for Transportation. The work plan in the proposal was asked to include several tasks focused on the provision of technical training to the public transit agencies in Iowa. The tasks documented in the work plan include the development and offering of three workshops on different subjects that will be offered either online or on-site. Two of the subjects have been identified by the Iowa DOT and a third will be selected from the responses to a training and/or technical assistance needs assessment that will also be completed as part of the project. The results of this assessment will be summarized and shared with a technical advisory committee for the selection process. As currently proposed, the third workshop will be offered on-site in Ames and the other two will be online.

About the research

An increasing number of concrete overlay projects in Iowa and around the United States have used fiber-reinforced concrete (FRC) mixtures. Fibers provide residual strength to concrete mixtures, and concrete overlay design procedures currently assume that fiber reinforcement enhances fatigue life. A number of studies have suggested that fibers may offer a number of additional performance benefits to concrete overlays. This study conducted a field investigation of six different concrete overlay sites in Iowa. Three of these sites contained test sections with varying thickness and joint spacing designs, and with and without fiber reinforcement. The field investigation performed a variety of tests to measure properties such as joint activation behavior, load transfer, structural response, pavement smoothness, and curling and warping behavior. This test regime allowed for a broad characterization of many aspects of the behavior and performance of concrete overlays, both with and without fiber reinforcement. The results indicated that, to date, fiber reinforcement did not appear to have a significant impact on load transfer, smoothness, or curling and warping at these concrete overlay sties. However, the comprehensive testing regime provided a number of insights into other aspects of concrete overlay design and performance, both with and without fiber reinforcement. The bond between concrete and asphalt was particularly important, even when the overlays were not intentionally designed to bond to the underlying asphalt layer. Finally, the report for this project also contains an appendix detailing a separate investigation of the behavior of FRC pavements placed without transverse joints.

About the research

Effective and timely bridge inspections are crucial for extending bridge lifespans and preventing catastrophic failures. Traditional inspection methods often involve manual visual assessments and can be time-consuming, labor-intensive, and prone to human error. Recent technological advancements in unmanned aerial vehicles (UAVs), artificial intelligence (AI), and machine learning (ML) offer promising solutions to these challenges. When high-quality images captured by UAVs are analyzed using AI and ML algorithms, structural defects can be detected and quantified with greater precision and efficiency than manual inspections.

The primary objective of this research was to enhance the accuracy and efficiency of structural inspections by integrating UAV technology for image capture and AI-based detection models for analysis. High-resolution images of bridge components were collected using UAVs operating at various distances and angles and were then processed through a custom-developed convolutional neural network (CNN) to detect critical defects such as cracking and spalling. The model’s performance was assessed through multiple case studies, and its ability to detect and quantify defects under different conditions was validated against field data. This approach yielded significant improvements over traditional bridge inspection methods in terms of the precision with which structural vulnerabilities were identified and accurately quantified defect dimensions.

Furthermore, the research incorporated the development of three-dimensional (3D) models of bridge structures using commercially available software to enable detailed structural assessments. High-resolution UAV imagery was successfully integrated into 3D modeling software to generate detailed models of bridge structures enabling comprehensive structural assessments and allowing for the quantification of detected defects. The results demonstrate the potential of UAV-based inspections combined with AI-powered detection models to revolutionize bridge inspection practices by offering a more reliable, efficient, and cost-effective approach to infrastructure maintenance and supporting more informed decision-making for infrastructure safety and longevity.