Institute for Transportation

About the research

In recent years, the Iowa Department of Transportation (DOT) as well as several other state DOTs have made increasing use of drilled shaft foundations on bridge projects. Due to soil variability and the lack of redundancy, the Iowa DOT typically requires that a bi-directional Osterberg cell (O-cell) load test be performed on a demonstration shaft at each new bridge project. The load test results are then used to verify the predicted capacity, and often to adjust the values of geotechnical shaft resistances used in designing the shafts for the entire bridge. However, O-cell tests are very costly (around $100k per test), and often provide inconclusive results, as only the upper or lower portion of the shaft (or neither) actually reach failure. As a result, extrapolation is commonly necessary to estimate the expected load-displacement behavior of the bridge foundations under the actual top-down loading conditions.

To address these shortcomings, this research investigates the use of top-down load tests on reduced-scale drilled shafts and develops scaling relations to predict the load-displacement curves of the full-scale shafts. Test results from the reduced-scale shafts will be compared to those from a planned full-scale O-cell test at an Iowa DOT bridge project site.

The research will contribute to the Midwest Transportation Center (MTC) theme of Data Driven Performance Measures for Enhanced Infrastructure Condition, Safety, and Project Delivery. Specifically, the project will contribute load-test data for the DSHAFT load and resistance factor design (LRFD) calibration database for drilled shafts, while enhancing the safety of the infrastructure system through more accurate and reliable design methods for drilled shaft foundations. The final products of this research will include design guides and tech-transfer materials for immediate use of the technology by the practicing engineers.

Funding Sources:
Federal Highway Administration State Planning and Research Funding
Iowa Department of Transportation
Iowa Highway Research Board ($100,000.00)
Midwest Transportation Center
USDOT/OST-R ($100,000.00)
Total: $200,000.00

Contract Number: DTRT13-G-UTC37

About the research

During winter road maintenance operations, the Iowa Department of Transportation (DOT) is responsible for servicing 24,000 lane miles of roadways, including Interstates, US highways, and Iowa roads. This project focused on operations for District 3, located in northwest Iowa, which services about 4,000 lane miles from 20 depots.

Two optimization problems were solved to determine the optimal snowplow routes in this district. The first problem was to design winter maintenance truck routes for single depots under the district’s current responsibility maps. The second problem was to design routes for multiple depots with intermediate facilities, with the service boundaries among the depots able to be redesigned. Both optimization problems were solved as capacitated arc routing problems (CARPs) using a memetic algorithm (MA) and considering the constraints of road segment service cycle time, heterogeneous vehicle capacities, fleet size, road-vehicle dependency, and work duration.

The results from solving the single-depot optimization problem show a 13.2% reduction in deadhead distance compared to current operations. The deadhead savings could be even larger because while the optimized routes strictly satisfy all constraints, the current operations might not. For the multiple-depot optimization problem, due to the network structure and current depot locations, the difference between the optimized routes based on a multiple-depot configuration and those based on a single-depot configuration is insignificant.

About the research

Iowa’s maximum speed limit for rural interstates has been 70 mph since 2005, and the Iowa legislature has recently discussed the possibility of further increasing the maximum speed limit. This research aims to inform this discussion by examining how traffic fatality rates have changed over time as maximum speed limits have been increased in Iowa and other states, with emphasis on the changes resulting from the more recent increases to 75 mph and above in other states.

The study included state-level and road-level analyses using nationwide data sets and an Iowa-specific analysis using data from within the state. The nationwide analyses confirm prior research showing that states with higher rural interstate speed limits experience a higher number of traffic fatalities. The state-level analysis shows that this effect is even larger when accounting for the proportion of rural interstate mileage in each state posted at the maximum speed limit. However, this increase in traffic fatalities may begin to taper off at the highest speed limits. The road-level analysis indicates that speed limit more strongly affects fatal crashes involving driver distraction than total fatalities or fatal crashes. Additionally, fatal crashes involving speeding are more strongly affected by speed limit on roads posted at 70 or 75 mph than on roads posted at 80 mph.

A simple before-and-after comparison of fatal and serious crash rates on Iowa interstates from 1991 to 2017 shows that crashes increased in the few years after the 2005 speed limit increase but have generally declined since then. Further analyses showed that average and 85th percentile speeds were influenced by roadway geometric characteristics and that speed variance was the primary factor affecting crash rate. The impacts of speed variance are most pronounced for the most severe crashes.

About the research

Winter highway maintenance is an annual multi-billion dollar operation aimed at improving the safety and mobility of the highway system. To help the winter highway maintenance agencies optimize the usage of resources, it is important to develop a performance measurement system that can evaluate how well maintenance activities have been performed. In Iowa Highway Research Board Project TR-491, researchers developed a performance measure based on average vehicle speed, which takes into account severity of the storm. The model uses six categorical variables to define a storm and compute the acceptable traffic speed drop.

A previous Iowa Department of Transportation (DOT) agreement developed a sequential Bayesian dynamic model based on the model in TR-491, which is capable of predicting the acceptable drops during the storm, and allow uncertainty in input variables (sensor measurements) to propagate into uncertainty in speed reduction. One limitation of the sequential Bayesian model is that its uncertainty measure does not account for model uncertainty and the uncertainty in human-weather interaction. The model in TR-491 is based on survey of expert opinion, and its uncertainty is not considered in the original development and our follow up work. The uncertainty in human behavior under different weather conditions is also not considered due to lack of time.

The Iowa DOT is interested in refining this sequential Bayesian model to produce more accurate real-time prediction of traffic speed drops with better uncertainty measures so that it can be used to evaluate the performance of snow/ice removal efforts and the effectiveness of different snow removal methods. Ultimately, the DOT is interested in using this model to help managers reallocate resources to optimize objective functions such as minimizing the total costs or the speed drops. The DOT is interested in developing a dynamic model capable of predicting in real-time acceptable drops in traffic speed on highways during major weather events with realistic uncertainty measures. The primary usage of such model is to evaluate the performance of highway winter maintenance operations and optimize resource allocation.

The researchers developed a model to relate weather variables to traffic flow changes at a local level. Weather station data and maintenance crew reports were used to develop an empirical adaptive stochastic model using a Bayesian formulation. Data from early time segments provide a prior quantification of the expected effects of weather variables on traffic speed over subsequent time segments. Data in the next time segment are then used to adjust these quantifications to reflect observed traffic speeds during that period. Thus, rather than explicitly determining numerous temporally dependent interactions, the main effects associated with key factors are allowed to undergo small shifts over time to fit the data. The model incorporates an autoregressive error structure to reflect temporal dependencies in observations that occur at reasonably high frequencies.

About the research

Pavement markings provide critical guidance to motorists, especially under dark (un-lit) conditions. However, the ability to see pavement markings on a wet, rainy night is problematic given that the presence of water considerably decreases pavement marking retroreflectivity.

This project evaluated the performance of several all-weather pavement marking products in an effort to provide guidance on their use on Illinois Department of Transportation (IDOT) roadways. In addition, a laboratory evaluation was completed in an effort to simulate degradation mechanisms of these pavement markings so that future all-weather materials can be evaluated in a timely manner within the laboratory rather than on public roadways.

The study found that only 15 percent of the all-weather products provided a retroreflectivity of 50 millicandelas per meter squared per lux (mcd/m²/lux), which is noted as (mcd) within the report, under continuous wetting conditions.

The laboratory evaluation showed some promise for the dry retroreflectivity performance given that data variability was low and there the correlation was good initially with the field data. The correlation was not as good, however, as the markings aged, and correlation in wet conditions was not good either.

About the research

For this project, an innovative wide joint was designed with a roughened interface surface, shrinkage-compensating concrete, and reinforcement steel. The researchers built and tested a specimen that consisted of two box beams and one innovative intermediate joint under early-age thermal loading and cyclic live loading in the laboratory. During these tests, no cracking was found in the joint and no trend of increasing differential displacement was found between the two beams over the course of millions of live load and thermal cycles.

Based on the results of the literature review and laboratory tests, this wide joint between the roughened interface surface, filled with shrinkage-compensating concrete and reinforced by reinforcement steel, can create a crack-free joint without the utilization of a shear key or transverse post-tensioning.

This joint is as functional as the traditional cement grout-filled narrow joint with respect to the transfer of the moment and shear between the girders, while also performing better than the traditional joint in resisting joint cracks in both early-age loading and the long-term service life of the bridge. At the same time, the test results for the new innovative joint detail appear to compare very well with the ultra-high performance concrete (UHPC) based joint detail developed and tested previously by the Federal Highway Administration (FHWA). However, the UHPC joint may have greater durability due to the very low material permeability

To further investigate the performance of this joint detail, the researchers recommend that a field trial be completed. During this field trial, the bridge should be monitored and evaluated during early-age concrete curing as well as for a period of at least two years following construction.

About the research

This research serves as a beginning point to explore new ways to support timely and accurate decision making during winter operations given the massive stream of data coming from the Iowa Department of Transportation (DOT) snowplow fleet. The Iowa DOT Maintenance Bureau manages roughly 900 snowplows, which are equipped and continuously transmitting important operational data every few seconds during winter operations. These data provide truck locations using automated vehicle location (AVL) pings and report operational status such as whether the plow is up or down and which materials, if any, are being applied to the roadway.

This research project created visual and tabular summaries of one day of winter operations data to provide practical information based on the interest and needs of both administrative and district maintenance staff. Future efforts can consider integrating these summaries and similar tools into daily operations.

This project includes the results of an attempt to conduct an analysis of snowplow blade performance using periodic measurements from specific trucks at the beginning of, and regularly throughout, two winter seasons. Unfortunately, the analysis was not possible given that snowplow operators are faced with too many demands and providing these driver-reported blade measurements was problematic, even with the significant efforts made and refined to secure the data over a second winter season. These efforts are described along with a framework that can be used for future efforts to complete this analysis.

About the research

Lack of funding and a desire to effectively manage the pavement network has resulted in the widespread use of chip seals by local agencies in Ohio. With the 2002 Construction and Materials Specifications (CMS), the Ohio Department of Transportation’s (ODOT) made major revisions to the chip seal specification to incorporate best practices applicable for pavements on the state highway system. However, the new specification may be burdensome and costly for local agencies to adopt due to lack of inspection personnel and a required level of quality which may not be necessary to achieve satisfactory performance on the local system. Many local agencies construct chip seals using local work crews and application rates based on experience, or with contractors using local specifications or older version of the ODOT specification. Consequently, success has been varied, with some excellent applications and some failures. The purpose of this research was to gain a better understanding of chip seal practices of the local agencies and identify best practices for low traffic volume roads. The goal of this research was to assess the current state of practice for chip sealing on county, township, and municipal-maintained roads. The objective was to develop a matrix of best practices for chip sealing low-volume roads in Ohio and design a study to aid in the future assessment of long-term performance creating protocols for data collection. As part of this study a literature review was completed, county and municipal engineers, and township trustees were surveyed regarding their chip seal practices, and follow-up interviews were conducted with eleven agencies. Based on the information collected a matrix of best practices for chip sealing on local roadways was developed and a study to collect long-term performance was designed. The best practices matrix identifies best practices as defined in the literature and by local agency personnel and is provided in this report. A plan and data collection software for a long term monitoring and evaluation of chip seals is also provided.

About the research

The objectives of this project were to validate design assumptions and evaluate the performance of the structural components and construction approaches provided in the design documents for a pretensioned, prestressed concrete beam-supported partial-depth precast deck system with cantilever precast overhang panels.

To achieve the objectives, laboratory tests were conducted on two small-scale specimens with horizontal loading on the barrier and vertical loading at various locations of the deck panels. The deck of each specimen generally consisted of two precast, cantilever overhangs, two precast, prestressed interior panels, and a portion of the cast-in-place (CIP) concrete deck.

The specimen details and construction work were carefully documented. The results indicated that the high-density polyethylene foam has sufficient stiffness and strength to support the precast deck panels and the construction load during concrete placement of the deck. The leveling bolt with normal polyethylene foam worked fine to support the deck panel and to resist the lateral concrete load. However, special attention during the gluing of the polyethylene foam is needed to ensure a good bond between the girder/deck concrete surface and the polyethylene foam.

The load test results indicated that both types of interior panels have an ultimate load capacity of about 240 to 250 kips when subjected to point load causing punching shear failure, exceeding the demands of the bridge service life. The composite action between the CIP and precast deck concrete is functional through the load application process, and no debonding or sliding was found at the horizontal interface between the CIP and precast concrete.

About the research

Increasing the cost-effective life of our nation’s bridges (sometimes known as the service life) is a very high national infrastructure priority. In fact, a recent Second Strategic Highway Research Program (SHRP2) Project (R19A) was specifically dedicated to developing tools for designing bridges to meet specifiable service-life design criteria. More specifically, Project R19A was intended to develop procedures, approaches, and details that would ensure that bridges have service lives beyond 100 years.

There is a current effort being undertaken by the National Academies to implement certain components of the R19A project report. As has historically been the case, the Iowa Department of Transportation (DOT) is playing a leading role in the implementation of R19A by actively demonstrating the integration of the recommendations in typical bridge replacement projects. (Examples of other Iowa DOT demonstrations of life-increasing design details include implementing jointless bridge configurations and the use/development of a low-slump/high density deck overlay concrete.)

The Iowa DOT is currently involved in two projects to integrate the results of R19A. In one project, the Iowa DOT utilized A1010 steel for the exterior girders of a bridge over I-29 in Woodbury County, Iowa. The second project is a unique endeavor by the Iowa DOT to design and construct side-by-side bridges on I-35 near Ames, Iowa. One bridge was designed using current practices, procedures, and details while the other will be designed using service life design procedures. Because these two bridges will be exposed to the same environmental conditions, very similar traffic, and will be constructed within the same timeframe, a unique opportunity exists to identify and evaluate differences in performance between the two bridges.

The goals of this work are as follows:

• Collect behavior information for two uniquely designed bridges (the second implementation mentioned above) and compare the impact of using service life design procedures
• Collect information needed to complete service life designs of other bridges