Improving Transition Outcomes: Capacity Building Forum: Dissemination of Promising Transition Practices

Information on the Promising Transition Practices shared at the September 28, 2007 Capacity Building Forum sponsored by Improving Transition Outcomes with Iowa Vocational Rehabilitation Services.

Evaluation of Different Methods to Calculate Heavy-Truck VMT, Final Report, December 2004

Reliable estimates of heavy-truck volumes are important in a number of transportation applications. Estimates of truck volumes are necessary for pavement design and pavement management. Truck volumes are important in traffic safety. The number of trucks on the road also influences roadway capacity and traffic operations. Additionally, heavy vehicles pollute at higher rates than passenger vehicles. Consequently, reliable estimates of heavy-truck vehicle miles traveled (VMT) are important in creating accurate inventories of on-road emissions. This research evaluated three different methods to calculate heavy-truck annual average daily traffic (AADT) which can subsequently be used to estimate vehicle miles traveled (VMT). Traffic data from continuous count stations provided by the Iowa DOT were used to estimate AADT for two different truck groups (single-unit and multi-unit) using the three methods. The first method developed monthly and daily expansion factors for each truck group. The second and third methods created general expansion factors for all vehicles. Accuracy of the three methods was compared using n-fold cross-validation. In n-fold cross-validation, data are split into n partitions, and data from the nth partition are used to validate the remaining data. A comparison of the accuracy of the three methods was made using the estimates of prediction error obtained from cross-validation. The prediction error was determined by averaging the squared error between the estimated AADT and the actual AADT. Overall, the prediction error was the lowest for the method that developed expansion factors separately for the different truck groups for both single- and multi-unit trucks. This indicates that use of expansion factors specific to heavy trucks results in better estimates of AADT, and, subsequently, VMT, than using aggregate expansion factors and applying a percentage of trucks. Monthly, daily, and weekly traffic patterns were also evaluated. Significant variation exists in the temporal and seasonal patterns of heavy trucks as compared to passenger vehicles. This suggests that the use of aggregate expansion factors fails to adequately describe truck travel patterns.

Ultra-Thin Portland Cement Concrete Overlay Extended Evaluation, January 2005

In this day of the mature highway systems, a new set of problems is facing the highway engineer. The existing infrastructure has aged to or past the design life of the original pavement design. In many cases, increased commercial traffic is creating the need for additional load carrying capacity, causing state highway engineers to consider new alternatives for rehabilitation of existing surfaces. Alternative surface materials, thicknesses, and methods of installation must be identified to meet the needs of individual pavements and budgets. With overlays being one of the most frequently used rehabilitation alternatives, it is important to learn more about the limitations and potential performance of thin bonded portland cement overlays and subsequent rehabilitation. The Iowa ultra-thin project demonstrated the application of thin portland cement concrete overlays as a rehabilitation technique. It combined the variables of base preparation, overlay thickness, slab size, and fiber enhancement into a series of test sections over a 7.2-mile length. This report identifies the performance of the overlays in terms of deflection reduction, reduced cracking, and improved bonding between the portland cement concrete (PCC) and asphalt cement concrete (ACC) base layers. The original research project was designed to evaluate the variables over a 5-year period of time. A second project provided the opportunity to test overlay rehabilitation techniques and continue measurement of the original overlay performance for 5 additional years. All performance indicators identified exceptional performance over the 10-year evaluation period for each of the variable combinations considered. The report summarizes the research methods, results, and identifies future research ideas to aid the pavement overlay designer in the successful implementation of ultra-thin portland cement concrete overlays as an lternative pavement rehabilitation technique.

Evaluation of Temporary Ramp Metering for Work Zones, 2012

Ramp metering has been successfully implemented in many states to improve traffic operations on freeways. Studies have documented the positive mobility and safety benefits of ramp metering. However, there have been no studies on the use of ramp metering for work zones. This report documents the results from the first deployment of temporary ramp meters in work zones in the United States. Temporary ramp meters were deployed at seven urban short-term work zones in Missouri. Safety measures such as driver compliance, merging behavior, and speed differentials were extracted from video-based field data. Mobility analysis was conducted using a calibrated simulation model and the total delays were obtained for under capacity, at capacity, and over capacity conditions. This evaluation suggests that temporary ramp meters should only be deployed at work zone locations where there is potential for congestion and turned on only during above-capacity conditions. The compliance analysis showed that non-compliance could be a major safety issue in the deployment of temporary ramp meters for under-capacity conditions. The use of a three-section instead of a traditional two-section signal head used for permanent ramp metering produced significantly higher compliance rates. Ramp metering decreased ramp platoons by increasing the percentage of single-vehicle merges to over 70% from under 50%. The accepted-merge-headway results were not statistically significant even though a slight shift towards longer headways was found with the use of ramp meters. Mobility analysis revealed that ramp metering produced delay savings for both mainline and ramp vehicles for work zones operating above capacity. On average a 24% decrease in total delay (mainline plus ramp) at low truck percentage and a 19% decrease in delay at high truck percentage conditions resulted from ramp metering.

Evaluation of Crushed Limestone Rock as a Mulch Material, HR-171, 1975

Earthen fills and back slopes resulting from highway building and other construction projects pose problems with respect to erosion stabilization and establishing vegetation cover. Sediments from such slopes create stream pollution while the erosion itself results in maintenance problems. Furthermore, adverse conditions aggravated by erosion prevent satisfactory establishing of vegetative cover. A dense vegetative cover is very effective in controlling erosion but even with optimum weather and soil conditions there is a delay of about 10 weeks between seeding and the establishment of a vegetative cover. Under actual field conditions, 3 months to a year may elapse between completion of construction and establishment of a vegetative cover. A research project was initiated early in 1974 to determine the effectiveness of a rock mulch of crushed limestone aggregates in controlling soil losses on highway construction back slopes in Iowa and to find the influence of such treatments on stand establishment of grasses and legumes.

Development of Bridge Load Testing Process for Load Evaluation, TR-445, 2003

Recent reports indicate that of the over 25,000 bridges in Iowa, slightly over 7,000 (29%) are either structurally deficient or functionally obsolete. While many of these bridges may be strengthened or rehabilitated, some simply need to be replaced. Before implementing one of these options, one should consider performing a diagnostic load test on the structure to more accurately assess its load carrying capacity. Frequently, diagnostic load tests reveal strength and serviceability characteristics that exceed the predicted codified parameters. Usually, codified parameters are very conservative in predicting lateral load distribution characteristics and the influence of other structural attributes. As a result, the predicted rating factors are typically conservative. In cases where theoretical calculations show a structural deficiency, it may be very beneficial to apply a "tool" that utilizes a more accurate theoretical model which incorporates field-test data. At a minimum, this approach results in more accurate load ratings and many times results in increased rating factors. Bridge Diagnostics, Inc. (BDI) developed hardware and software that are specially designed for performing bridge ratings based on data obtained from physical testing. To evaluate the BDI system, the research team performed diagnostic load tests on seven "typical" bridge structures: three steel-girder bridges with concrete decks, two concrete slab bridges, and two steel-girder bridges with timber decks. In addition, a steel-girder bridge with a concrete deck previously tested and modeled by BDI was investigated for model verification purposes. The tests were performed by attaching strain transducers on the bridges at critical locations to measure strains resulting from truck loading positioned at various locations on the bridge. The field test results were used to develop and validate analytical rating models. Based on the experimental and analytical results, it was determined that bridge tests could be conducted relatively easy, that accurate models could be generated with the BDI software, and that the load ratings, in general, were greater than the ratings, obtained using the codified LFD Method (according to AASHTO Standard Specifications for Highway Bridges).

Field and Laboratory Evaluation of Precast Concrete Bridges, TR-440, 2001

Recent data compiled by the National Bridge Inventory revealed 29% of Iowa's approximate 24,600 bridges were either structurally deficient or functionally obsolete. This large number of deficient bridges and the high cost of needed repairs create unique problems for Iowa and many other states. The research objective of this project was to determine the load capacity of a particular type of deteriorating bridge – the precast concrete deck bridge – which is commonly found on Iowa's secondary roads. The number of these precast concrete structures requiring load postings and/or replacement can be significantly reduced if the deteriorated structures are found to have adequate load capacity or can be reliably evaluated. Approximately 600 precast concrete deck bridges (PCDBs) exist in Iowa. A typical PCDB span is 19 to 36 ft long and consists of eight to ten simply supported precast panels. Bolts and either a pipe shear key or a grouted shear key are used to join adjacent panels. The panels resemble a steel channel in cross-section; the web is orientated horizontally and forms the roadway deck and the legs act as shallow beams. The primary longitudinal reinforcing steel bundled in each of the legs frequently corrodes and causes longitudinal cracks in the concrete and spalling. The research team performed service load tests on four deteriorated PCDBs; two with shear keys in place and two without. Conventional strain gages were used to measure strains in both the steel and concrete, and transducers were used to measure vertical deflections. Based on the field results, it was determined that these bridges have sufficient lateral load distribution and adequate strength when shear keys are properly installed between adjacent panels. The measured lateral load distribution factors are larger than AASHTO values when shear keys were not installed. Since some of the reinforcement had hooks, deterioration of the reinforcement has a minimal affect on the service level performance of the bridges when there is minimal loss of cross-sectional area. Laboratory tests were performed on the PCDB panels obtained from three bridge replacement projects. Twelve deteriorated panels were loaded to failure in a four point bending arrangement. Although the panels had significant deflections prior to failure, the experimental capacity of eleven panels exceeded the theoretical capacity. Experimental capacity of the twelfth panel, an extremely distressed panel, was only slightly below the theoretical capacity. Service tests and an ultimate strength test were performed on a laboratory bridge model consisting of four joined panels to determine the effect of various shear connection configurations. These data were used to validate a PCDB finite element model that can provide more accurate live load distribution factors for use in rating calculations. Finally, a strengthening system was developed and tested for use in situations where one or more panels of an existing PCDB need strengthening.

Evaluation of Post-Tension Strengthened Steel Girder Bridge Using FRP Bars, 2003

Many state, county, and local agencies are faced with deteriorating bridge infrastructure composed of a large percentage of relatively short to medium span bridges. In many cases, these older structures are rolled or welded longitudinal steel stringers acting compositely with a reinforced concrete deck. Most of these bridges, although still in service, need some level of strengthening due to increases in legal live loads or loss of capacity due to deterioration. Although these bridges are overstressed in most instances, they do not warrant replacement; thus, structurally efficient but cost-effective means of strengthening needs to be employed. In the past, the use of bolted steel cover plates or angles was a common retrofit option for strengthening such bridges. However, the time and labor involved to attach such a strengthening system can sometimes be prohibitive. This project was funded through the Federal Highway Administration’s Innovative Bridge Research and Construction program. The goal is to retrofit an existing structurally deficient, three-span continuous steel stringer bridge using an innovative technique that involves the application of post-tensioning forces; the post-tensioning forces were applied using fiber reinforced polymer post-tensioning bars. When compared to other strengthening methods, the use of carbon fiber reinforced polymer composite materials is very appealing in that they are highly resistant to corrosion, have a low weight, and have a high tensile strength. Before the post-tensioning system was installed, a diagnostic load test was conducted on the subject bridge to establish a baseline behavior of the unstrengthened bridge. During the process of installing the post-tensioning hardware and stressing the system, both the bridge and the post-tensioning system were monitored. The installation of the hardware was followed by a follow-up diagnostic load test to assess the effectiveness of the post-tensioning strengthening system. Additional load tests were performed over a period of two years to identify any changes in the strengthening system with time. Laboratory testing of several typical carbon fiber reinforced polymer bar specimens was also conducted to more thoroughly understand their behavior. This report documents the design, installation, and field testing of the strengthening system and bridge.

Nondestructive Evaluation and Assessment of Concrete Barriers for Defects and Corrosion, 2013

Wiss, Janney, Elstner Associates, Inc. (WJE) evaluated potential nondestructive evaluation (NDE) methodologies that may be effective in 1) identifying internal defects within slip formed concrete barriers and 2) assessing the corrosion condition of barrier dowel bars. The evaluation was requested by the Bridge Maintenance and Inspection Unit of the Iowa Department of Transportation (IaDOT) and the Bureau of Bridges and Structures of the Illinois Department of Transportation (IDOT). The need arose due to instances in each Department’s existing inventory of bridge barriers where internal voids and other defects associated with slip forming construction methods were attributed to poor barrier performance after completion of construction and where, in other barrier walls, unintentional exposure of the dowel bars revealed extensive corrosion-related section loss at previously uninspectable locations, reducing the capacity of the barriers to resist traffic impact loads. WJE trial tested potential NDE techniques on laboratory mock-up samples built with known defects, trial sections of cast-in-place barriers at in-service bridges in Iowa, and slip formed and cast-in-place barrier walls at in-service bridges in Illinois. The work included review of available studies performed by others, field trial testing to assess candidate test methods, verification of the test methods in identifying internal anomalies and dowel bar corrosion, and preparation of this report and nondestructive evaluation guidelines.