The Effect of Four-Lane to Three-Lane Conversion on the Number of Crashes and Crash Rates in Iowa Roads, June 2005

We analyze crash data collected by the Iowa Department of Transportation using Bayesian methods. The data set includes monthly crash numbers, estimated monthly traffic volumes, site length and other information collected at 30 paired sites in Iowa over more than 20 years during which an intervention experiment was set up. The intervention consisted in transforming 15 undivided road segments from four-lane to three lanes, while an additional 15 segments, thought to be comparable in terms of traffic safety-related characteristics were not converted. The main objective of this work is to find out whether the intervention reduces the number of crashes and the crash rates at the treated sites. We fitted a hierarchical Poisson regression model with a change-point to the number of monthly crashes per mile at each of the sites. Explanatory variables in the model included estimated monthly traffic volume, time, an indicator for intervention reflecting whether the site was a “treatment” or a “control” site, and various interactions. We accounted for seasonal effects in the number of crashes at a site by including smooth trigonometric functions with three different periods to reflect the four seasons of the year. A change-point at the month and year in which the intervention was completed for treated sites was also included. The number of crashes at a site can be thought to follow a Poisson distribution. To estimate the association between crashes and the explanatory variables, we used a log link function and added a random effect to account for overdispersion and for autocorrelation among observations obtained at the same site. We used proper but non-informative priors for all parameters in the model, and carried out all calculations using Markov chain Monte Carlo methods implemented in WinBUGS. We evaluated the effect of the four to three-lane conversion by comparing the expected number of crashes per year per mile during the years preceding the conversion and following the conversion for treatment and control sites. We estimated this difference using the observed traffic volumes at each site and also on a per 100,000,000 vehicles. We also conducted a prospective analysis to forecast the expected number of crashes per mile at each site in the study one year, three years and five years following the four to three-lane conversion. Posterior predictive distributions of the number of crashes, the crash rate and the percent reduction in crashes per mile were obtained for each site for the months of January and June one, three and five years after completion of the intervention. The model appears to fit the data well. We found that in most sites, the intervention was effective and reduced the number of crashes. Overall, and for the observed traffic volumes, the reduction in the expected number of crashes per year and mile at converted sites was 32.3% (31.4% to 33.5% with 95% probability) while at the control sites, the reduction was estimated to be 7.1% (5.7% to 8.2% with 95% probability). When the reduction in the expected number of crashes per year, mile and 100,000,000 AADT was computed, the estimates were 44.3% (43.9% to 44.6%) and 25.5% (24.6% to 26.0%) for converted and control sites, respectively. In both cases, the difference in the percent reduction in the expected number of crashes during the years following the conversion was significantly larger at converted sites than at control sites, even though the number of crashes appears to decline over time at all sites. Results indicate that the reduction in the expected number of sites per mile has a steeper negative slope at converted than at control sites. Consistent with this, the forecasted reduction in the number of crashes per year and mile during the years after completion of the conversion at converted sites is more pronounced than at control sites. Seasonal effects on the number of crashes have been well-documented. In this dataset, we found that, as expected, the expected number of monthly crashes per mile tends to be higher during winter months than during the rest of the year. Perhaps more interestingly, we found that there is an interaction between the four to three-lane conversion and season; the reduction in the number of crashes appears to be more pronounced during months, when the weather is nice than during other times of the year, even though a reduction was estimated for the entire year. Thus, it appears that the four to three-lane conversion, while effective year-round, is particularly effective in reducing the expected number of crashes in nice weather.

Design Procedures and Field Monitoring of Submerged Barbs for Streambank Protection, June 2007

The main objective of this study was to evaluate the hydraulic performance of riprap spurs and weirs in controlling bank erosion at the Southern part of the Raccoon River upstream U.S. Highway 169 Bridge utilizing the commercially available model FESWMS and field monitoring. It was found based on a 2 year monitoring and numerical modeling that the design of structures was overall successful, including their spacing and stability. The riprap material incorporated into the structures was directly and favorably correlated to the flow transmission through the structure, or in other words, dictated the permeable nature of the structure. It was found that the permeable dikes and weirs chosen in this study created less volume of scour in the vicinity of the structure toes and thus have less risk comparatively to other impermeable structures to collapse. The fact that the structures permitted the transmission of flow through them it allowed fine sand particles to fill in the gaps of the rock interstices and thus cement and better stabilize the structures. During bank-full flows the maximum scour hole was recorded away from the structures toe and the scourhole size was directly related to the protrusion angle of the structure to the flow. It was concluded that the proposed structure inclination with respect to the main flow direction was appropriate since it provides maximum bank protection while creating the largest volume of local scour away from the structure and towards the center of the channel. Furthermore, the lowest potential for bank erosion also occurs with the present set-up design chosen by the IDOT. About 2 ft of new material was deposited in the area located between the structures for the period extending from the construction day to May 2007. Surveys obtained by sonar and the presence of vegetation indicate that new material has been added at the bank toes. Finally, the structures provided higher variability in bed topography forming resting pools, creating flow shade on the leeward side of the structure, and separation of bed substrate due to different flow conditions. Another notable environmental benefit to rock riprap weirs and dikes is the creation of resting pools, especially in year 2007 (2nd year of the project). The magnitude of these benefits to aquatic habitat has been found in the literature that is directly related to the induced scour-hole volume.

Final report on the Portable Weather Station, March 2012

This station was required to have air temperature, relative humidity, wind speed and direction, and pavement temperature sensors of similar quality to the traditional RWIS sensors, have an integrated solar powered battery system, and be trailer-mounted for ease of transport. The station was tested by the Iowa DOT for basic reliability and sensor performance for a month and a half in Ames, Iowa before being moved to near Osceola, Iowa in early February 2010 for further field testing and evaluation. DOT field maintenance staff was able to successfully set up the station with minimal instruction and found the station to be relatively intuitive in its installation. Air temperature, wind speed, and wind direction observations from the station were compared to a nearby RWIS station and had good agreement. Pavement temperature readings were compared to sites within 40 miles of the station, and the readings correlated. The station has had good reliability.

Making a Library Beginning : How a Library May Be Started in a Small Town (Iowa Library Commission Leaflet No. 11)

A short booklet from the Iowa Library Commission containing advice on how small towns can start and set up public libraries for their communities.

Investigation of the Loss of Prestress in Prestressed Concrete Beams due to Steam Curing, HR-62, 1961

Mass production of prestressed concrete beams is facilitated by the accelerated curing of the concrete. The ·method most commonly used for this purpose is steam curing at atmospheric pressure. This requires concrete temperatures as high as 150°F. during the curing period. Prestressing facilities in Iowa are located out of doors. This means that during the winter season the forms are set and the steel cables are stressed at temperatures as low as 0°F. The thermal expansion of the prestressing cables should result in a reduction of the stress which was placed in them at the lower temperature. If the stress is reduced in the cables, then the amount of prestress ultimately transferred to the concrete may be less than the amount for which the beam was designed. Research project HR-62 was undertaken to measure and explain the difference between the initial stress placed in the cables and the actual stress which is eventually transferred to the concrete. The project was assigned to the Materials Department Laboratory under the general supervision of the Testing Engineer, Mr. James W. Johnson. A small stress bed complete with steam curing facilities was set up in the laboratory, and prestressed concrete beams were fabricated under closely controlled conditions. Measurements were made to determine the initial stress in the steel and the final stress in the concrete. The results of these tests indicate that there is a general loss of prestressing force in excess of that caused by elastic shortening of the concrete. The exact amount of the loss and the identification of the factors involved could not be determined from this limited investigation.

Oils and Tars from Iowa Shales, HR-32, 1962

The inadequate supply of suitable road surfacing material in the southern part of Iowa raises the question of the possibility of utilizing certain shales abundant in this area. These carbonaceous shales commonly overlie the coal beds and may also be found as impurities in the coal seams. They constitute the "slate" which with minor amounts of coal makes up the "gob" piles at the mines. These shales frequently contain enough carbonaceous material to burn. Those which do not usually require only a relatively small amount of coal mixed with them to support combustion. As a result, the "gob" piles frequently burn. The residual shale material is frequently used locally as a road surfacing material. However, since there is no control over the burning, there is no assurance that the product is the most suitable which might be produced or that it is even uniform in its properties. To determine if a controlled burning would produce a suitable road building product economically a research project "Use of Shales as Highway Materials" (ISHC Project HR-21, IEES Project 299-S) was set up in the Iowa Engineering Experiment Station with funds provided by the Iowa State Highway Commission, This project was supervised by Charles Frush, formerly Assistant Professor of Mining Engineering at Iowa State University. The various shales were subjected to controlled burning, and the solid residues were tested for their suitability for highway use.

Determination of Flood Dischard Characteristics of Small Drainage Areas, HR-3, Progress Report, 1960

Project HR-3 of the Iowa Highway Research Board has been active since October 1, 1950. The project objective is the determination of flood discharge characteristics of small drainage areas. Funds for the project amount to $10,000 per year of which, by cooperative agreement, the Highway Commission and the U. S. Geological Survey each furnish $5,000. Previous reports have explained the set-up of the project and these explanations will not be repeated in this report.

Cathodic Protection for a Continuous Box Girder Bridge Deck, HR-553, 1993

Bridge deck deterioration due to corrosive effect of deicers on reinforcing steel is a major problem facing many agencies. Cathodic protection is one method used to prevent reinforcing steel corrosion. The application of a direct current to the embedded reinforcing steel and a sacrificial anode protects the steel from corrosion. This 1992 project involved placing an Elgard Titanium Anode Mesh Cathodic Protection System on a bridge deck. The anode was fastened to the deck after the Class A repair-work and the overlay was placed using the Iowa Low Slump Dense Concrete System. The system was set up initially at 1 mA/sq ft.

Evaluation of Lightweight Profilers for Construction Smoothness Evaluation, MLR-02-02, 2004

High-speed non-contact laser profilers have become the standard testing equipment for pavement management ride quality testing. The same technology used in the high-speed profilers is now being used in lightweight profilers for construction smoothness testing. The lightweight profilers have many advantages over the California 25-ft profilograph. Despite the many advantages of the lightweight profilers, there is resistance from the contracting industry toward eliminating the 25-ft profilograph for construction ride testing. One way to reduce or overcome the resistance is to evaluate and demonstrate the advantages/disadvantages of the lightweight profiler in actual field use in Iowa. The objective of the study was to purchase a lightweight profiler and to evaluate its suitability for construction smoothness quality verification and quality acceptance on Iowa projects. A lightweight profiler, an Ames Engineering, Inc. LISA single laser unit, was received in February 2003 for the study. Based on the work done during the 2003 construction season, the following conclusions can be made: (1) For hot mix asphalt surfaces, the LISA correlated well with the contractors' profilographs; (2) LISA results are significantly affected by longitudinal tining on portland cement concrete pavements, requiring a laser system upgrade to give accurate results; (3) A significant timesaving was realized by using the LISA; (4) Increasing visibility and reducing time in the construction zone improved safety; (5) One person with limited lifting capabilities could set up and operate the LISA; and (6) With the current Iowa Department of Transportation specification, the LISA cannot totally replace the profilograph, since bridges and short segments with no adjoining pavement would still require a profilograph.

Comparison of Setting Time Measured Using Ultrasonic Wave Propagation with Saw-Cutting Times on Pavements, TR-675, 2015

At present, there is little fundamental guidance available to assist contractors in choosing when to schedule saw cuts on joints. To conduct pavement finishing and sawing activities effectively, however, contractors need to know when a concrete mixture is going to reach initial set, or when the sawing window will open. Previous research investigated the use of the ultrasonic pulse velocity (UPV) method to predict the saw-cutting window for early entry sawing. The results indicated that the method has the potential to provide effective guidance to contractors as to when to conduct early entry sawing. The aim of this project was to conduct similar work to observe the correlation between initial setting and conventional sawing time. Sixteen construction sites were visited in Minnesota and Missouri over a two-year period. At each site, initial set was determined using a p-wave propagation technique with a commercial device. Calorimetric data were collected using a commercial semi-adiabatic device at a majority of the sites. Concrete samples were collected in front of the paver and tested using both methods with equipment that was set up next to the pavement during paving. The data collected revealed that the UPV method looks promising for early entry and conventional sawing in the field, both early entry and conventional sawing times can be predicted for the range of mixtures tested.

06003-002 Upper Catfish Creek Watershed Final Report

Upper Catfish Creek is located in a 9,300-acre watershed that flows through two significant natural resources, Swiss Valley Park and Swiss Valley Nature Preserves, one of the largest nature preserves in the Midwest. According to DNR’s 2002 305(d) report, that portion of the creek within the park and preserve is classified as a Class B(CW) cold water stream of which a portion has naturally reproducing trout (one of only 30 in the state of Iowa with this capability). Urban sprawl is a real threat to the Upper Catfish Creek Watershed. Currently, 10% of the watershed is residential, but 27% is zoned residential or commercial. The watershed is near Dubuque city limits but the jurisdiction is in the county. Differing criteria for land development between city and county jurisdictions further entices developers to build in outlying areas. County leaders agree there is more that needs to be done and will work with municipalities on uniformity of regulations and follow-up measures. We propose to set up key urban conservation practice models that will address storm water runoff and water quality which can be learned about and viewed by city and county officials, engineers, developers, etc. This would be part of a larger initiative including an educational campaign, inter-jurisdictional planning, the development of a land use GIS database, and agricultural conservation practices. The successes coming out of and learned about this watershed will serve as a model to spread county-wide.

Work Zone Simulation Model, 1999

To support the analysis of driver behavior at rural freeway work zone lane closure merge points, Center for Transportation Research and Education staff collected traffic data at merge areas using video image processing technology. The collection of data and the calculation of the capacity of lane closures are reported in a companion report, "Traffic Management Strategies for Merge Areas in Rural Interstate Work Zones". These data are used in the work reported in this document and are used to calibrate a microscopic simulation model of a typical, Iowa rural freeway lane closure. The model developed is a high fidelity computer simulation with an animation interface. It simulates traffic operations at a work zone lane closure. This model enables traffic engineers to visually demonstrate the forecasted delay that is likely to result when freeway reconstruction makes it necessary to close freeway lanes. Further, the model is also sensitive to variations in driver behavior and is used to test the impact of slow moving vehicles and other driver behaviors. This report consists of two parts. The first part describes the development of the work zone simulation model. The simulation analysis is calibrated and verified through data collected at a work zone in Interstate Highway 80 in Scott County, Iowa. The second part is a user's manual for the simulation model, which is provided to assist users with its set up and operation. No prior computer programming skills are required to use the simulation model.