Institute for Transportation

About the research

The project evaluated two pre-manufactured pavement marking tapes (380AW and XRP-R) over three winter seasons at two different Illinois DOT locations (central and southern Illinois). The two products were installed on I-80 within a recessed groove in contrast to IL-3 where they were rolled in with the last pass of the asphalt finishing machine. Retroreflectivity was measured under three standard conditions including dry, wet-recovery, and continuously wetted. The 380AW tape measured 148 mcd under continuously wetted conditions after 3 winters on I-80 and overall measured significantly higher than the XRP-R tape under the two wet conditions (recovery and continuously wetted). The XRP-R tape performed well under dry conditions; however, wet-recovery retroreflectivity was below 100 mcd (after initial conditions) and continuously wetted retroreflectivity did not exceed 100 mcd. Short of a minimum retroreflectivity threshold for wet conditions, these findings will support IDOT decision making in terms of product selection where trying to enhance safety through providing higher levels of wet night visibility. The findings also highlight the potential negative impacts on performance when rolling these products in as opposed to placing them within a groove.

About the research

While for decades horizontally curved steel girder bridges have been a solution for constructing interchanges between state and Interstate highways, concerns remain regarding their design and construction. The cross-frames in these bridges are especially critical because, unlike in straight bridges, they are major load carrying elements.

The design and analysis of cross-frames in curved bridges is complex due to complexities in how loads are transmitted throughout these types of bridges. However, a unique opportunity exists to improve the design of these components using modern computer software and short- and long-term monitoring.

This project investigated a horizontally curved bridge located in Story County near Ames, Iowa, to understand the behavior of cross-frames during construction and over the service life of the bridge. The project involved a numerical investigation using finite element modeling and short-term and long-term monitoring in the field to (1) identify sections of the bridge to instrument under dead, live, and temperature loading; (2) evaluate the performance of cross-frames through long-term monitoring; (3) evaluate the performance of cross-frames using live load tests; and (4) provide recommendations for practice.

The research results suggest that the cross-frames close to supports may experience high stress levels, and therefore special attention is required for their design compared to the other cross-frames. The cross-frames within the interior bays were also found to carry higher forces than those in the outer bays. This situation requires additional analysis during design to ensure the safety and performance of curved girder bridges.

About the research

This project is a task order under the main Federal Highway Administration (FHWA)-sponsored project, “Infrastructure Research and Technology Deployment Program.”

The U.S. has more than 600,000 bridges, making the distributed load rating and posting processes across the nation a significant effort that does and can benefit from improvements in efficiency. Bridge load rating, posting, and overweight permitting processes evolve due to the regulatory requirements regarding the frequency of inspections and relevant changes to bridges that necessitate re-rating them. These factors include changes to the dead load, strength of members, and any maintenance or rehabilitation work.

As such, States are interested in modifying their procedures to implement technology and improved means and

methods to reduce the time associated with load rating. Being able to load rate bridges efficiently and accurately is a necessity, particularly in the use case of permit load routing.Based on the extensive findings during the information collection processes for this project, frameworks for future

bridge load rating, posting, and overweight permitting were developed to improve productivity, efficiency, and consistency by closing process gaps and through the application of newer technologies. The newer technologies include digital twin concepts; integrating various (new) data; creating, updating, and reusing models; integrating sensing data (bridge, traffic, weigh-in-motion); and better analysis methods.

This work may help develop the state of practice.

About the research

Computer vision algorithms have been improved significantly to provide accurate detection, tracking, and recognition of objects in general. Available public datasets are crucial for extracting key features thanks to ever developing machine learning and deep learning algorithms. Since cameras are becoming vastly available to be employed on vehicles to extract useful information for both autonomous driving and intelligent driver assistance, we are aiming to develop intelligent driver state estimation algorithms that are based on state-of-the-art detection and recognition using computer vision. One of the main drawbacks for naturalistic driving data is having low-resolution and noisy video data that limits the overall accuracy when we test with the models trained on clear images. The research team has proposed (1) a comprehensive AI platform for data management, modeling, and enhanced annotations; (2) video quality enhancement using deep models, (3) face detection at acute angles, and (4) recurring network-based driver state estimation.

About the research

Coarse aggregate, depending on intended usage, constitutes roughly 20–45% of portland cement concrete as well as being a major component in the construction of granular surface roads and shoulders for paved roads. However, coarse aggregate quality greatly varies among sources based on its petrophysical properties. Therefore, it is important to understand how these properties emerge from the depositional and diagenetic history of a deposit in order to accurately predict pavement durability, which can be negatively impacted by oscillating freeze/thaw cycles. To derive more information about a coarse aggregate’s pore system, this study used a “third generation” Iowa Pore Index (IPI) device capable of measuring the volume of intruded water at various time intervals ranging from 0.1–2.0 seconds, as well as measuring intrusion at variable pressures up to 70 psi (480 kPa). Using this new device, 21 carbonate samples (10 dolostones and 11 limestones) were compared to “traditional” IPI measurements. The new method gave slightly higher primary loads.

Additionally, with cumulative volume plotted for the first five minutes of intrusion, dolostones and limestones with elevated primary loads stood apart from the remaining, less macroporous limestone sources. By decreasing apparatus chamber size, higher total intrusion was recorded and IPI values were more correlative with traditional measurements. However, by analyzing the effect of variable pressure intrusion (15, 35, and 60 psi), it was observed that the transition point between intrusion of macropores and micropores was sample-dependent based on lithological properties (i.e., porosity, connectivity of pores, and pore-throat sizes). Although prior methods utilized 60 seconds as this transition point, incremental intrusion data suggest most samples complete macropore intrusion within the first 12 seconds. Therefore, by assessing the incremental intrusion of each source, new primary and secondary loads were calculated, which may be more characteristic of individual lithologies. As a result, secondary load values increased as more intrusion was accounted to micropores than through utilization of the previous method.

With further study, this method could better predict the longevity and overall durability of coarse aggregate based on pore structure in a more individualized fashion than the previous IPI method.

About the research

Buchanan County, Iowa, has been working with the National Center for Wood Transportation Structures and a timber fabricator to develop the next-generation timber bridge. The goal is to increase the structural efficiency of timber bridges and increase longevity by (1) creating a composite deck-girder system and (2) using an epoxy overlay. These design elements have the potential to increase viable bridge options for use not only on Iowa’s roadways, but nationally and internationally as well.

The bridge system developed for this research was a composite glue-laminated (glulam) girder-deck system utilizing epoxy for the connection and an epoxy overlay wearing surface on the deck. This design was investigated through small- and large-scale laboratory testing of the composite epoxy connection and a field demonstration bridge built utilizing this girder to deck connection detail and epoxy overlay.

The small-scale tests showed that the best overall joint connection is an epoxy and lag bolt connection. The joints with epoxy at least tripled the shear capacity of the lag bolt joint, and addition of mechanical fasteners to the epoxy connection marginally increased performance. The large-scale laboratory tests showed a small increase in the load capacity and movement of the neutral axis when the deck panels are affixed to the girders, both of which indicate potential composite action. Furthermore, the epoxied connection exhibited an improved composite connection over the lag bolt connection.

Three live load tests on the field demonstration bridge in 2015, 2016, and 2017 indicated that transverse load distribution for all load cases was adequate. The composite action observed was not likely substantial enough to be accounted for in design. The chip seal shows signs of cracking at the transverse deck panel joints, but because of the epoxy the joints remain sealed and show no signs of moisture intrusion on the underside of the deck. The epoxy wearing surface on the deck performed better as an impermeable joint filler than a wearing surface.

About the research

In cold climates, the modern method for making durable portland cement concrete (PCC) pavement has been to entrain air in the paste. This method enables the formation of an air void network that permits the drainage of liquid water and accommodates pressure increases during freezing conditions. The Iowa Department of Transportation (DOT) has required air entrainment since the mid-1950s, and yet some pavements constructed before this period show little to no deterioration and remain in service. It remains uncertain which properties have allowed these pavements to last so long and if these properties can be used to increase the durability or reduce the cost of modern pavement designs.

This project aimed to study the evolution of pore networks in pre-1950 and post-1950 Iowa PCC pavements and interpret the deterioration of pavement aggregates. For this study, helium pycnometry was used to examine the total connected porosity of the air void network. Computed tomography (CT) scanning was used to cross-validate the helium porosity results as well as to calculate pore and aggregate size distributions. Mercury porosimetry was used to identify pore-throat size distributions and cross-validate the CT-measured values. Samples were also thin sectioned to characterize the physical state of coarse aggregate particles, determine their lithology, and identify their modes of deterioration. Finally, a script was developed for the coding platform, MATLAB, to provide similar metrics to the RapidAir 457 Air Void Analyzer but for CT images (e.g., porosity, pore size distribution, grain size distribution).

The initial hypothesis motivating this study was that pores forming around and inside deteriorating coarse aggregate particles in some unusually durable pre-air-entrainment PCC pavements are connected through pore throats in the paste serving to create effective air void networks. It was instead found through this study that the porosity of pavements showed strong correlation between decreasing porosity and increasing age. These results indicate that PCC porosity can be predicted from pavement age, at least in Iowa. Petrographic data suggest that this phenomenon is due to a reduction of pore space in the paste, with the reduction in paste porosity having more impact than the increase in porosity due to coarse and fine aggregate deterioration.

About the research

The National Pollutant Discharge Elimination System General Permit No. 2 requires the Iowa Department of Transportation (DOT) to develop a stormwater pollution prevention plan for all construction activities that are covered by the permit. The Stormwater Pollution Prevention Plan includes the design, installation, and maintenance of erosion and sediment control (E&SC) practices to minimize downstream impact from stormwater discharges. The Iowa DOT has specifications, standard drawings, and guidance for the design of E&SC practices, but these practices had not been formally evaluated for field performance.

This research aimed to understand the performance of current E&SC practices and enhance the design guidance available to the Iowa DOT. Silt fence ditch checks, wattle ditch protection, silt fence perimeter control, and temporary sediment control basins were monitored for performance on US 30 in Tama County, Iowa. Two modified silt fence ditch check installations had an average of 2.5 and 4 times as much sediment accumulation as a standard silt fence, the modified wattle ditch protection had 13.15 times the sediment retention of a standard wattle installation, and silt fence perimeter control modifications led to less T-post deflection and failures observed than with the standard installation.

A temporary sediment control basin was monitored as a single basin and as basins in series. In the single basin, turbidity increased by an average 92 nephelometric turbidity units (NTUs) after residence in the basin, whereas the basins in series provided a turbidity reduction of 215 NTUs in the first basin and 870 NTUs in the second basin. However, the system of basins provides negligible turbidity reduction.

In addition to field monitoring, laboratory flume testing was conducted to compare the hydraulic performance of wattles. Average depth and length ratios were calculated for each tested wattle in addition to the percent difference between the wattle and an impervious weir and were classified from Class 1–4 with Class 1 being the least effective and Class 4 being the most effective at reducing supercritical flows. From flume testing, straw wattles meet Class 2; coconut coir, wood chips, and synthetic fiber wattles fall into Class 3; and miscanthus fiber would qualify as Class 4.

This field study provided researchers insight on the performance of standard and several trial modified E&SC practices. Controlled testing should continue to verify results observed in the field.

About the research

Maintaining optimal mobility on high-volume arterial traffic corridors is important to transportation agencies and the public. Corridor performance often can be enhanced by updating traffic signal timing, but most agencies find it necessary to prioritize their retiming efforts based on resource constraints. To facilitate prioritization, a set of arterial corridor performance measures was developed using INRIX probe vehicle data. These commercially available data are derived from in-vehicle global positioning system (GPS) observations transmitted wirelessly, eliminating the need for supplemental traffic observation infrastructure to be installed in the field.

The main objective of this study was to present a methodology to compare arterial corridors in terms of mobility-based performance measures. This process can help agencies select the corridors that are in need of signal retiming and can help identify corridors suited for adaptive signal control implementation. The two-step methodology began by identifying the number of days in a year with abnormal traffic patterns and comparing the volume-normalized performance of the remaining segments to identify corridors that are problematic on normal days.

The proposed methodology was applied to 12 corridors in Des Moines, Iowa, and 1 in Omaha, Nebraska. Three corridors were found to have a high number of anomalous days. Among the remaining corridors, three were identified as under-performing on normal days. In addition, the impact of implementing an adaptive signal control system on one corridor (University Avenue) was evaluated, where small improvements in travel rate and daily variation were observed, but the overall variability increased.

Funding Sources:
Federal Highway Administration State Planning and Research Funding
Iowa Department of Transportation ($47,758.00)
Midwest Transportation Center
USDOT/OST-R ($46,040.00)
Total: $93,798.00

Contract Number: DTRT13-G-UTC37

About the research

Maintaining effective pavement markings year-round is a challenge in Iowa, where winter maintenance causes so much damage due to the harsh winter exposure from snow plow blades, sand, and salt brine. Given these conditions, and a limited painting season, it is critical that agencies select the proper pavement marking materials for the roadways in their network.

The overarching objective of this work was to support the Iowa Department of Transportation (DOT) Pavement Marking Task Force (PMT) in achieving better pavement markings statewide.

While the initial scope of this project was to evaluate different durable markings and pavement grooving configurations in an effort to make better choices for year-round markings, limited funding, difficulty in finding a contractor for a small test site, and adverse weather conditions caused the project to be revised to omit the field evaluation.

Instead, the project focused on supporting PMT decision making in light of challenging financial conditions, and particularly supporting efforts to determine paint truck and material choices by looking at peer states, and also by looking at contracting options for installation on the state system.

Pavement markings play a critical role in guiding motorists and delineating roadways for safe travel. The identification and use of more durable pavement markings may be the key to improving visibility, operations, and—most importantly—safety.