Illinois Tollway Research Articles

Impacts of road salt on seed germination of Thuja occidentalis found in natural communities adjacent to the Illinois Tollway in northeastern IL, USA

In the USA, road salt usage in urban areas has increased since the 1950s. In the greater Chicago area over 175 000 tons of salt are applied every year. The salt runoff from this application has the potential to negatively impact nearby plants and alter native plant communities. We evaluated how varying salt concentrations affect overall germination, germination probability, and multiple metrics of germination speed for seeds from five source populations of Thuja occidentalis L. Two populations in a native forested fen system are susceptible to salt runoff from the Illinois Tollway. We found that increased salt concentrations decreased both the probability of germination and overall germination, and increased the time to germination. Seeds from the two natural populations performed poorly compared to the other populations. Salt pollution impacts the health and survival of adult trees, and may also inhibit the reproduction and recruitment of T. occidentalis. Reduction of salt pollution is necessary to maintain the long-term survival and persistence of this species, other sensitive species, and native fen habitats.

Development of a Performance-Related Framework for Asphalt Mixture Design for the Illinois Tollway

Various agencies have begun to research and introduce performance-related specifications (PRS) for the design of modern asphalt paving mixtures. The focus of most recent studies has been directed toward simplified cracking test development and evaluation. In some cases, development and validation of PRS has been performed, building on these new tests, often by comparison of test values to accelerated pavement test studies and/or to limited field data. This study describes the findings of a comprehensive research project conducted at Illinois Tollway, leading to a PRS for the design of mainline and shoulder asphalt mixtures. A novel approach was developed, involving the systematic establishment of specification requirements based on: 1) selection of baseline values based on minimally acceptable field performance thresholds; 2) elevation of thresholds to account for differences between short-term lab aging and expected long-term field aging; 3) further elevation of thresholds to account for variability in lab testing, plus variability in the testing of field cores; and 4) final adjustment and rounding of thresholds based on a consensus process. After a thorough evaluation of different candidate cracking tests in the course of the project, the Disk-shaped Compact Tension—DC(T)—test was chosen to be retained in the Illinois Tollway PRS and to be presented in this study for the design of crack-resistant mixtures. The DC(T) test was selected because of its high degree of correlation with field results and its excellent repeatability. Tailored Hamburg rut depth and stripping inflection point thresholds were also established for mainline and shoulder mixes.

Recycled asphalt shingle modified asphalt mixture design and performance evaluation

The inclusion of recycled asphalt shingles (RAS) in asphalt mixtures has become increasingly common; however, the underlying design principles vary significantly by agency. The primary objectives of this study included: (1) evaluating the ‘binder availability’ concept for RAS mixtures through a carefully designed laboratory experiment; (2) demonstrating a balanced mixture performance testing approach for the design of RAS mixtures; and (3) evaluating the field data of RAS mixtures placed in the Midwest region of the U.S. Three asphalt mixture designs with RAS contents of 0, 2.5% and 5.0%, which were designed to have nearly identical volumetric characteristics, were investigated. The binder availability was determined to be approximately 100% in the two RAS mixtures considered. In addition, Hamburg wheel tracking and disk-shaped compact tension tests were conducted to evaluate the high- and low-temperature mixture performance. As expected, the addition of RAS significantly improved the rutting resistance. Disk-shaped compact tension (DC(T)) test results demonstrated that a soft base binder effectively permitted the design of thermal-crack-resistant RAS mixtures. Field investigations indicated that the performance of pavement surfaces containing RAS was similar to that of surfaces containing only reclaimed asphalt pavement or virgin materials. This study also highlights a performance-engineered mix design approach, which is currently being adopted by several agencies in the Midwest (e.g., Illinois Tollway, Missouri DOT, etc.) and can provide mix designers a reliable approach for designing innovative asphalt mixtures with higher recycling levels and a modern, heterogeneous composition. Furthermore, the proposed approach may prove to be a simpler, more mixture-centric alternative to the primary method suggested in AASHTO PP78-17, which recommends arbitrary VMA bumping plus binder extraction, recovery, and advanced binder testing. • Study aims at determining binder availability from RAS material in asphalt mixtures. • Virgin and RAS mixtures were designed with identical volumetric parameters and asphalt contents were compared. • Binder availability was determined to be approximately 100% for RAS mixtures. • Performance-based tests were used to characterize RAS mixtures. • Field observations of mixtures with RAS were reported.

Modern, Recycled SMA Mixtures on the Illinois Tollway and Preliminary Performance-Based Mix Design Approach

As more recycled materials are utilized in modern asphalt mixtures, the overall phenomenological behavior of this important infrastructure material becomes more complex than ever, accelerating the need to supplement volumetric-based mix testing procedures with mixture mechanical tests. This paper introduces a mixture performance test based design approach, as a supplement to the current Superpave volumetric mix design approach, which is being implemented by several agencies near Chicago, Illinois, USA. For research purposes, the practical design suite, which considers the high and low-temperature performance of asphalt mixtures through Hamburg wheel tracking and disk-shaped compact tension fracture testing, has been supplemented by additional testing and analysis including creep compliance, performance-space diagram construction, and thermal cracking modeling using the software program ILLI-TC. Field cores from seven Illinois Tollway sites in Chicagoland with welltracked pavement performance were tested and analyzed using the aforementioned methods. These modern, high-performance stone matrix asphalt (SMA) recycled mixtures contained recycled asphalt pavement (RAP), reclaimed asphalt shingles (RAS), and ground tire rubber (GTR), and used a 3.5% design void target to promote mix durability. Rutting and cracking test results, and thermal cracking modeling predictions, were found to be consistent with field observations indicating near-zero rutting and cracking levels after up to eight years of heavy tollway traffic and severe mid-continental environmental conditions. In addition, the Hamburg-DC(T) performance space diagram was used to further analyze the results, demonstrating how this plotting tool can be used to adjust future mix designs to yield even longer life on the Tollway system at little-to-no extra cost.

Performance Analysis of Asphalt Mixtures Modified with Ground Tire Rubber Modifiers and Recycled Materials

The usage of Ground Tire Rubber (GTR) in asphalt pavements has gained renewed interest due to its potential sustainability, economic, and performance benefits. This study focuses on asphalt mixtures designed with three different rubber modifier products including (1) a terminal-blend GTR, (2) a dry-process, chemically processed rubber product, and (3) a terminal-blend rubber-polymer hybrid product. The modifications were incorporated into Illinois Tollway’s approved Stone Matrix Asphalt (SMA) designs using (1) a base binder (PG 58-28), (2) a softer binder (PG 46-34), and (3) a softer binder with higher recycled content. Disk-shaped Compact Tension (DC(T)) test, Hamburg Wheel Tracking Test (HWTT) and Acoustic Emission (AE) tests were performed to characterize the mixtures. The fracture energy for most mixtures met the stringent criteria of 690 J/m2 and the rut depths measured were less than 6 mm at 20,000 wheel passes. A Hamburg-DC(T) plot suggests that higher amounts of RAP/RAS (RAP: Reclaimed Asphalt Pavement; RAS: Reusable Asphalt Shingles) can be successfully used if a suitably soft base binder is employed.

System-Level Approach for Identifying Main Uncertainty Sources in Pavement Construction Life-Cycle Assessment for Quantifying Environmental Impacts

Poor data quality in pavement construction life-cycle inventory (LCI) causes uncertainty in quantifying the associated environmental impact through life-cycle assessment (LCA). To reduce such LCA uncertainty while enhancing the reliability, several studies have been conducted on a screening procedure based on a quality assessment of the LCI input data to identify main sources of the resulting uncertainty. However, they often create additional uncertainty in the screening process and thus result in erroneous outcomes in identifying main uncertainty sources. This paper proposes a new system-level approach that enables the identification of main uncertainty sources through input data quality assessment upon reducing additional uncertainty. Based on the proposed preset criteria and by leveraging environmental emission quantities associated with each process, the authors first propose to achieve a consistent weighting process and then derive the system-level aggregated data quality indicator (ADQI). By utilizing the ADQI, system-level LCA uncertainty information is obtained through a modified beta distribution. The proposed method was evaluated through case studies on real-world pavement construction projects of the Illinois Tollway, and the main uncertainty sources, named key processes, were identified through sensitivity analyses. In the case studies, the plant operation, cement production, and binder production were identified as key processes in the given pavement construction project, contributing more than half of the total uncertainty resulting from poor data quality. Based on these findings, the proposed work is expected to help practitioners improve the reliability of pavement construction LCA through uncertainty-informed decision making to better reflect real project characteristics in the identified key processes.

Spatial Verification of Modulus for Pavement Foundation System

This paper presents the results of a field study recently completed on an Illinois Tollway construction project, in which intelligent compaction (IC) measurements were calibrated on site with in situ elastic modulus (E), resilient modulus (Mr), modulus of subgrade reaction ( k), and California bearing ratio (CBR) testing. The purpose of the field calibration was to generate geo-referenced spatial modulus maps that can be used for field verification of design input parameters. E values were obtained using light weight deflectometer (LWD), stress-dependent Mr values and static k values were obtained using automated plate load testing (APLT), and CBR values were obtained using a dynamic cone penetrometer (DCP). The IC measurements were obtained using a vibratory smooth drum roller outfitted with an index measurement value system, and a roller outfitted with a retrofit kit programmed to produce validated integrated compaction (VIC) measurements through a process of field calibration. Results showed that VIC based calibration can produce correlations with R2 > 0.9 with Mr and k values, and the VIC maps can be reliably used for quality assurance/verification testing. Although the index based IC measurement values showed statistically significant relationships, the R2 values were lower (<0.6). An implementation framework that emphasizes an independent certification approach for field calibration is being developed based on these test results for the Illinois Tollway, to aid in the effective implementation of the modulus-based mapping approach for pavement design field verification.

Enhancing pavement performance prediction models for the Illinois Tollway System

Accurate pavement performance prediction represents an important role in prioritizing future maintenance and rehabilitation needs, and predicting future pavement condition in a pavement management system. The Illinois State Toll Highway Authority (Tollway) with over 2000 lane miles of pavement utilizes the condition rating survey (CRS) methodology to rate pavement performance. Pavement performance models developed in the past for the Illinois Department of Transportation (IDOT) are used by the Tollway to predict the future condition of its network. The model projects future CRS ratings based on pavement type, thickness, traffic, pavement age and current CRS rating. However, with time and inclusion of newer pavement types there was a need to calibrate the existing pavement performance models, as well as, develop models for newer pavement types.This study presents the results of calibrating the existing models, and developing new models for the various pavement types in the Illinois Tollway network. The predicted future condition of the pavements is used in estimating its remaining service life to failure, which is of immediate use in recommending future maintenance and rehabilitation requirements for the network.

Validation of Staged Construction Pavement Design with the Falling Weight Deflectometer

In 2005, the Illinois Tollway staff rehabilitated a 33-mi-long segment of Interstate Highway 88 in Illinois by rubblizing deteriorated jointed plain concrete pavement (JPCP) and placing a hot-mix asphalt (HMA) overlay on the rubblized JPCP. The pavement design called for the ultimate pavement structure to be constructed in two stages: the first at the time of rubblization, when at least 6.0 in. of HMA would be placed, and the second 10 years later, when 2.0 in. of HMA would be cold milled and 6.0 in. of HMA placed back. The pavement design called on the tollway staff’s experience with rubblization and research surrounding the fatigue endurance limit to develop a staged construction strategy. The strategy would reduce up-front construction costs by placing a minimum of 6.0 in. of HMA at initial construction. The tollway staff was confident that the strategy would work, but the pavement performance was monitored annually for verification. Annual monitoring included pavement distress condition surveys, deflection testing and deflection data analysis, and pavement coring. In particular, the tollway staff desired confirmation that the staged construction strategy would yield a perpetual asphalt pavement by controlling the amount of bottom-up fatigue cracking that would develop in the asphalt mat. After 9 years of observations and data analysis, the staff has confirmed the pavement is exhibiting the properties of a perpetual pavement and the staged construction strategy should ultimately prove successful.

Large-Scale Deployment of Performance-Related Specifications for Jointed Plain Concrete Pavement

For the 2015 construction season, the Illinois Tollway management awarded nine contracts that include performance-related specifications for jointed plain concrete pavement (JPCP) to be placed along the I-90 corridor between Chicago and Elgin, Illinois. Overall, the nine contracts have a total value of over $550 million, with more than $50 million of the JPCP subject to performance-related specification incentives and disincentives. Deployment of this volume of performance-related paving has required the development of specifications and special provisions as well as a more focused approach to monitoring the testing of the concrete materials as paving is proceeding. Enhanced communication and documentation processes have also been created to ensure that the flow of materials test data and the impacts that the data are having on the calculation of incentives and disincentives can be transmitted to the contractors as quickly as possible. The communication processes include contractor responses and feedback to the materials test data and the financial impact resulting from the test data, with electronic documentation of communication between the testing labs, the tollway and its quality contractors, and the paving contractors. This study documents the development of the current performance-related JPCP specifications, including the challenges encountered in trying to establish performance-related specifications for such a large number of concurrent projects, the solutions employed to overcome those challenges, and the impact on both the tollway and the contractors as a result of the deployment of performance-related JPCP.

Scenarios Developed for Improved Sustainability of Illinois Tollway

This paper quantifies the environmental improvements in current versus past pavement materials and construction practices employed by the Illinois State Toll Highway Authority (tollway authority). Improvements in sustainability performance were measured with a life-cycle assessment (LCA) approach. Three scenarios were generated to evaluate tollway authority practices on the basis of eight 2013 Interstate reconstruction and rehabilitation projects. The first scenario, 2013 projects, analyzed the actual pavement material and designs of the 2013 projects. The second scenario, materials baseline, was based on the 2013 projects but modified to include mix designs with less-sustainable materials used by the tollway authority circa 2000. The third scenario, design and materials baseline, considered both mix designs and pavement design practices used circa 2000. To improve the spatial and temporal relevance of the analyses, two regional databases of life-cycle inventories representing processes from 2013 and 2000 were developed and applied to the 2013 projects and 2000 baselines. A tool developed by the Illinois Center for Transportation (ICT) of the University of Illinois at Urbana–Champaign, the pavement ICT-LCA 0.95, was used to evaluate the sustainability performance indicator (SPI), global warming potential (GWP), and cumulative energy demand (CED) for each scenario. The resultant savings in SPI, GWP, and CED from the first scenario ranged between 17% and 28%, 12% and 16%, and 13% and 26%, respectively, compared with the second scenario, and 12% and 33%, 8% and 26%, and 11% and 32%, respectively, compared with the third scenario.

Overlapping Start-Time Bands in Implicit Tour Scheduling

Many organizations face personnel scheduling decisions under conditions of variable demand for service across a seven-day planning horizon. These organizations must assign employees to daily shifts that efficiently satisfy the demand for labor, yet allow adequate time for rest between subsequent shifts of an employee's weekly tour schedule. To meet these diverse objectives, managers may permit shifts to begin (and end) in any planning period of the day, but place bands on shift-start times to which individuals may be assigned on each day of their tour schedule. We present a compact integer programming model that implicitly represents start-time band scheduling flexibility. We demonstrate the new model by applying it to requirements for toll collectors on the Illinois Tollway. Problems requiring up to two million variables using a general set covering formulation were represented using the new implicit programming model and often solved to optimality in just a few minutes on a Pentium-based microcomputer. The results indicate that start-time bands can provide an important improvement in scheduling efficiency when compared to the exclusive use of schedules that require workers to begin work on the same hour of the day on each day of their tour.

Performance of Prestressed Concrete on the Illinois Tollway After 25 Years of Service

The paper presents an overview of the performance of the precast prestressed concrete elements and structurs on the Illinois State Toll Highway after 25 years of service. The condition of the bridge girders, stay-in-place deck panels, bearings, and bridge piers, together with any evidence of corrosion and freeze-thaw damage are discussed.

Changes in fatal and nonfatal crash rates on a toll highway.

Rates of crashes, crashes with injuries, and crashes with fatalities were lower during the 6 months of March 1-August 31, 1974, following a 5-15 mph (8-24 kph) decrease in speed limits on the Illinois Tollway, than the corresponding rates for any of the 6 preceding years, 1968-1973. During the same months of 1968-1974, rates of crashes and of crashes with injuries showed peaks without consistent trends, but rates and percentages of fatal crashes decreased. The data agree with the hypothesis that reducing speed limits on toll roads may lead to substantial reductions in rate of crashes and injuries.

Solution of Acoustic and Vibration Problems in over-the-Road Restaurants

On the Illinois Tollway the restaurants are placed over the highway with a panoramic view in both traffic directions. Pace Associates were the architects and engineers. This construction introduced numerous acoustic and vibration problems: (1) Prevention of “shimmying” of tables caused by structure-borne vibration; (2) isolation of traffic noise; (3) reverberation control (the ceiling was an unusual design of cast concrete with 3-ft by 3-ft concave openings); (4) optimum background noise control; and (5) control of ventilation system noise from under-the-floor ducts. The solutions of these problems will be illustrated and measurement data shown. In the finished structures the loudest vehicles are hardly audible and there is no perceptible vibration.