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Open Access Publications from the University of California


Dedicated to providing knowledge, the University of California Pavement Research Center uses innovative research and sound engineering principles to improve pavement structures, materials, and technologies.

University of California Pavement Research Center

There are 168 publications in this collection, published between 1995 and 2023.
Guidelines (7)

Guidelines for the Selection, Specification, and Application of Chemical Dust Control and Stabilization Treatments on Unpaved Roads

Unacceptable levels of dust, poor riding quality, impassability in wet weather, and unsustainable maintenance and gravel replacement practices are experienced on most unpaved road networks, and although it is acknowledged that unpaved roads are fundamental to local, regional, and national economies, many current management practices used on these roads leave much to be desired. Over the past 100 years a range of chemical treatments has been developed to fill the need for reducing the environmental and social impacts of road dust, improving the performance and safety of unpaved roads, and/or improving the properties of marginal materials to the extent that a road can be given all-weather status or upgraded to a paved standard. Most of these chemical treatments are proprietary and there is often little documented information regarding the chemistry of the treatment, the results of experimental trials to determine under what conditions the chemical treatment will work best, or guidelines on where and how to use the treatment. Most unpaved road chemical treatments carry no formal specification nor do they adhere to formal environmental testing requirements. Consequently, there has been no large-scale effort to establish and/or implement formal unpaved road chemical treatment programs anywhere in the world, other than those used in site-specific industrial applications such as mining operations. This guide introduces a new process for selecting an appropriate chemical treatment category for a specific set of unpaved road conditions using ranked potential performance. The process is based on the practitioner setting an objective for initiating a chemical treatment program and understanding the road in terms of materials, traffic, climate, and geometry. Using the information collected, the most appropriate chemical treatment subcategories for a given situation can be selected from a series of charts and ranked using a simple equation. This process can be completed manually using a paper form, or by using a web-based ( or spreadsheet tool. Matrices for each of the objectives were developed based on documented field experiments and the experience of a panel of practitioners. Guidance on specification language for procuring and applying unpaved road chemical treatments is also provided, along with comprehensive guidance on understanding unpaved road wearing course material performance.

Pavement Preservation Studies Technical Advisory Guide

This document provides guidelines for the establishment, monitoring and reporting of pavement preservation experiments in California. Information is provided in chapters covering: Management and responsibilities, Project fundamentals, Experiment work plan, Site selection, Experiment construction, Experiment monitoring, Forensic investigations, Laboratory testing, Data analysis, reports and implementation, Data management and documentation, Example experiment work plans, checklists and form. The document aims to assist with achieving successful completion of experiments and implementation of the findings.

Pavement Preservation Studies Technical Advisory Guide: Summary

This document provides guidelines for the establishment, monitoring and reporting of pavement preservation experiments in California. Information is provided in chapters covering: Management and responsibilities, Project fundamentals, Experiment work plan, Site selection, Experiment construction, Experiment monitoring, Forensic investigations, Laboratory testing, Data analysis, reports and implementation, Data management and documentation, Example experiment work plans, checklists and forms The document aims to assist with achieving successful completion of experiments and implementation of the findings.

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Policy Briefs (1)

Heavier Alternative Fuel Trucks Are Not Expected to Cause Significant Additional Pavement Damage

Medium- and heavy-duty trucks on California’s roads are shifting from conventional gasoline and diesel propulsion systems to alternative fuel (natural gas, electric, and fuel cell) propulsion technologies, spurred by the state’s greenhouse gas (GHG) reduction goals. While these alternative fuel trucks produce fewer emissions, they are also currently heavier than their conventional counterparts. Heavier loads can cause more damage to pavements and bridges, triggering concerns that clean truck technologies could actually increase GHG emissions by necessitating either construction of stronger pavements or more maintenance to keep pavements functional. California Assembly Bill 2061 (2018) allows a 2,000-pound gross vehicle weight limit increase for near-zero-emission vehicles and zero-emission vehicles to enable these trucks to carry the same loads as their conventional counterparts. The law also asked the UC Institute of Transportation Studies to evaluate the new law’s implications for GHG emissions and transportation infrastructure damage. To conduct this analysis, researchers at UC Davis considered three adoption scenarios of alternative fuel trucks in two timeframes, 2030 and 2050 (Figure 1). Based on these scenarios, the researchers used life cycle assessment and life cycle cost analysis to evaluate how heavier trucks might affect pavement and bridge deterioration, GHG emissions, and state and local government pavement costs. The study did not evaluate the safety implications of increasing allowable gross vehicle weights.

Reprint Reports (6)

tBeam—A Fast Model to Estimate Energy Consumption Due to Pavement Structural Response User Manual

This document constitutes the user manual for tBeam, standalone software for the analysis of energy dissipation in pavements under moving vehicles. tBeam was developed as part of the improvement of modeling capabilities for environmental life cycle assessment of pavements being conducted by the University of California Pavement Research Center for the California Department of Transportation. tBeam is finite element based, employing multi-layered three-node Timoshenko beam elements resting on a viscoelastic Winkler foundation. It provides an approximation of the deflection bowl of pavements and the energy dissipated in pavement structures when subjected to loads moving at constant velocities. tBeam supports two loading options: a uniform pressure (per unit length) applied to a segment at the center of the beam, and a rolling rigid wheel. To achieve numerical efficiency the load-beam-foundation system is represented relative to a moving coordinate system attached to the moving load. The higher efficiency is made possible because, in this framework, an observer attached to the moving coordinate system perceives a “static” state (i.e., independent of time). The standalone tBeam software serves two purposes. First, to provide developers of pavement LCA tools a “guide” as to how to integrate tBeam technology into their program. To this end, the “main” of tBeam can be used as “guide” for integrating tBeam capabilities within the LCA tool. Second, tBeam capabilities are relevant to pavement research in general. Thus, it could represent a useful addition to the toolset for pavement viscoelastic mechanics.

Temperature Influence on Road Traffic Noise: Californian OBSI Measurement Study

The work described in this report is adjunct to a five-year study of tire/pavement noise undertaken by the University of California Pavement Research Center for the California Department of Transportation under the Partnered Pavement Research Center program (PPRC). This part of the study was performed in cooperation with the Danish Road Institute/Road Directorate, and it examined the influence of air temperature on tire/pavement noise measurements performed on two types of tires (Aquatred and Standard Reference Test Tire [SRTT]) on different asphalt pavement surfaces using the On-board Sound Intensity (OBSI) method. Field noise measurement testing was carried out in two series: one in the Southern California desert on State Route 138 using the SRTT, and the other with data collected on a statewide selection of pavements tested with the Goodyear Aquatred tire in an earlier part of the PPRC noise study. The field measurements yielded data for deriving air temperature coefficients for the two types of tires, and a comparison of them is made. A worldwide survey of the available literature accompanies the field work and analysis, and a summary of it is used to compare the air temperature coefficients of the SRTT with a combination of tire types used in European testing. In addition, findings in the literature serve as the basis for a series of predicted temperature coefficients for passenger cars on various cement concrete and asphalt pavements. Finally, the report presents ten general conclusions drawn regarding the relationship between air temperature correction and tire/road noise on asphalt and concrete pavements.

tBeam—A Fast Model to Estimate Energy Consumption Due to Pavement Structural Response: Theoretical and Validation Manual

One of the most important contributors to the environmental impacts from use of highways is the energy exerted by vehicles, particularly routes that carry higher volumes of traffic. Part of this energy is consumed by response of the vehicle’s tires and suspension to pavement surface roughness and macrotexture. Another part of the energy consumed is by energy dissipation due to the structural response of the pavement itself under the moving load. This document is the theoretical and validation manual tor tBeam, standalone software for the analysis of energy dissipation in pavements under moving vehicles. tBeam was developed as part of the improvement of modeling capabilities for environmental life cycle assessment of pavements being conducted the University of California Pavement Research Center for the California Department of Transportation. The energy consumed due to structural response are controlled by the structural properties of the pavement which are dependent on the time of day, the season, and the condition (damage) of the pavement. The energy dissipation also depends on the speed and weight of each moving wheel load. As a result, estimating the lifetime energy dissipated in a pavement structure requires multiple analyses considering the thousands of permutations of these variables for a given segment of the highway network. Therefore, models for pavement-vehicle energy dissipation must balance two opposing needs: obtaining a reasonably accurate estimate of the dissipated energy, and high numerical efficiency. For numerical efficiency, the tBeam software employs a one-dimensional finite-element based solution of a wheel traveling at a constant velocity on a viscoelastic beam-foundation system, and a further reduction of numerical effort is obtained by formulating the model relative to a moving coordinate system attached to the wheel. The one-dimensional solution is, by nature, an approximation to the three-dimensional world. This approximation can be improved by incorporating a “correction factor,” which is based on comparisons with pavement simulations accounting for the double curvature observed in loaded pavements. In this report prediction disparity for a single structure is studied. The results show a clear trend where the correction factor decreases with rising temperature, and increases with higher velocity. The present study was insufficient to establish a law for the correction factor even for the single case studied. The correction factor ranged from about 1.25 at low temperature and high velocity to about 0.6 for high temperature and low velocity. The first part of this report presents the underlying theory for tBeam and implementation details. The second part presents closed form solutions for specialized pavement-foundation systems. The third component of the report presents some of the validation simulations undertaken to demonstrate the performance of tBeam, including comparisons with closed form solutions provided in this report, and recommendations for further development of tBeam.

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Research Reports (148)

Framework and Demonstration of Simulations of Environmental Impacts from Traffic on Highway Construction Work Zones

The objective of this study was to develop a framework for determining the fuel use and environmental impacts caused by construction work zones (CWZs) on a range of vehicles and to produce initial calculations of these impacts by modeling traffic closure conditions for highway maintenance and rehabilitation (M&R) activities. The framework was developed and demonstrated in several scenarios. The study included three common highway categories—freeways, multi-lane highways, and two-lane highways—and common California vehicle types. The framework uses realistic drive cycle values and CWZ operation scenarios as inputs to the simulation software MOtor Vehicle Emission Simulator (MOVES) to estimate total fuel consumption and air pollutant emissions. In this study, the framework was demonstrated using three CWZ operations under different traffic congestion levels: light, medium, and heavy.

Fuel consumption and pollutant emissions results obtained for the CWZ operation scenario with and without congestion were compared with those for a no-CWZ, no-congestion scenario. In the simulation results for a freeway with a CWZ and heavy congestion, fuel consumption increased by 85% and the CO2 equivalent (CO2-e) emissions increased by 86%, NOx by 62%, SOx by 85%, and PM2.5 by 128%. In the multi-lane highway scenarios, fuel consumption increased by 85%, and CO2-e emissions increased by 88%, NOx by 75%, SOx by 87%, and PM2.5 emissions by 129% for a CWZ with heavy congestion. Lessening traffic congestion in a CWZ from heavy (average speed 5 mph) to medium (average speed 25 mph for a freeway section and 15 mph for a multi-lane road section) reduced fuel consumption by 40% on a freeway and 33% on multi-lane highway.

This study also included use of a pilot car in a CWZ on a two-lane road. This approach was undertaken to estimate the possible benefits of different CWZ lane closure strategies and traffic management plans. The pilot-car operation scenario results indicate that a one-lane closure with pilot-car operation on a two-lane road might consume 13% more fuel because of idling time and the slow movement of vehicles following the pilot car. This scenario generated emissions increases of 10% for CO2-e, 14% for NOx, 13% for SOx, and 65% for PM2.5.

The results of these scenarios indicate that the impacts from heavy vehicles far exceed those from smaller vehicles in CWZs. Phase 2 of the study will develop methods for pavement management, conceptual evaluation, and project design that consider construction closures by implementing this life cycle assessment framework. These methods will also be used in studies to evaluate pavement design lives (20 years versus 40 years) and pavement selection for truck lanes and in-place recycling and to evaluate lane closure schedules and tactics to minimize CWZ impacts on highways by using project-specific traffic congestion levels.

Pavement ME JPCP Transverse Cracking Model Calibration and Design Catalog Framework (Version 2.5.5)

The Mechanistic-Empirical Pavement Design Guide (MEPDG) is a comprehensive method, including models and guidance, developed in 2002 by the American Association of State Highway and Transportation Officials (AASHTO) to analyze and design both flexible and rigid pavements. The MEPDG is implemented in a software called Pavement ME. The MEPDG models were calibrated using data from the Long-Term Pavement Performance (LTPP) sections from throughout the United States, including some from California. The MEPDG recommends that nationally calibrated models be validated using local data and, if necessary, recalibrated. This recommendation is particularly applicable to the Caltrans road network, considering the climate and materials differences between California and the rest of the nation. The first step in recalibrating Pavement ME is to perform a sensitivity analysis to identify which variables are most important and to look for results that do not match expected performance. This was the subject of a previous report titled Pavement ME Sensitivity Analysis. Based on the sensitivity analysis, the decision was made to perform a new calibration of the MEPDG models as implemented in Pavement ME software. A new approach was developed for the calibration. This new approach uses network-level performance data from the pavement management system (PMS) with orders of magnitude more observations and length of pavement than are used in the traditional approach and in the national calibration of the MEPDG models. The framework does not require sampling of materials from specific sections in the network. Rather, it uses the statewide median values from mechanistic testing from a representative sample of materials across the network. Variability of performance and reliability of design (probability that the design will meet or exceed the design life) is accounted for through separate consideration of within-project and between-project variability. The calibration reduced significant bias in the application of the nationally calibrated models to California. This report presents the results of the application of the new procedure to calibrate the Pavement ME transverse cracking model for jointed plain concrete pavements (JPCP). The California pavement management system (PaveM) database—with about 4600 lane-miles of JPCP built on 446 lane replacement projects completed between 1947 and 2017—was used to calibrate the transverse cracking model in Pavement ME. The nationally calibrated Pavement ME transverse cracking model prediction on the PaveM performance database has bias and standard error of 13.3% and 23.03%, respectively. After calibration, the bias and standard error of the locally calibrated model decreased to 0.039% and 5.69%, respectively.

Development of an Empirical-Mechanistic Model of Overlay Crack Progression using Data from the Washington State PMS Database

This is the second of two reports that present fatigue cracking performance models for asphalt concrete overlays placed on existing asphalt concrete pavement. The models were developed from the pavement management system (PMS) database of the Washington State Department of Transportation (WSDOT). The database included existing pavement structure, overlay thickness and type, truck traffic, and observed percent of the wheelpath cracked from annual condition surveys. Climate data was developed by the UCPRC to augment the WSDOT data. This report presents a model for crack propagation, starting from crack initiation, which was defined as 5 percent of the wheelpath with longitudinal cracking. The combined initiation and propagation models were included in a spreadsheet calculator which was used to perform an analysis of the sensitivity of crack initiation and propagation to the input variables. The models are extremely useful for predicting pavement performance. For use in California they will need recalibration of the coefficients to reflect differences in WSDOT and California practice, primarily the use of thicker overlays in California, placement of overlays at much more advanced states of cracking in the existing pavement, and possible differences in routine maintenance activities.

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Technical Memoranda (5)

Smoothness Monitoring of Selected Concrete Surfaces

In late 2015, Caltrans requested that 26 recently constructed concrete projects be tested for smoothness in terms of the International Roughness Index (IRI). The stated purpose was to observe measured IRI on projects accepted after a standard special provision (SSP) change that Caltrans made in 2013 and that was incorporated into the 2015 Construction Contract Standards. The projects provided 52 test sections for evaluation, consisting of three types of paving work: (1) diamond grind on existing pavement, (2) new continuously reinforced concrete pavement, and (3) new jointed plain concrete pavement. The project plans had completion dates from May 2010 to December 2014, and contract acceptance dates from April 2014 to October 2015. Caltrans did not identify which projects had the new SSP or specification change in its contract documents. The IRI data were collected from October 2016 to December of 2016. The IRI data collected included the effects of paving, any corrective grinding required to meet contract acceptance, and the increased roughness caused by traffic over post-construction periods of one to more than two and a half years. At the time of testing in 2016, the UCPRC test vehicle was equipped with a point laser in the left wheel path and a wide spot laser in the right wheel path. The data presented in this technical memorandum are primarily from the wide spot laser because the current standards require the wide spot laser. In general, the IRI measured by a point laser can be unduly increased due to the surface texture of the pavement, which is part of the reason for moving toward a wide spot laser. The construction specification considers both wheel paths and not just the right wheel path tested in this project. The IRI data using the wide spot laser in the right wheel path alone showed that 22% of the 0.1 mi. long sections met the construction standard of 60 in./mi. when measured one to two and a half years after construction. Based on the results from the right wheel path and the wide spot laser, 67% of the right wheel path sections are in good condition with IRI values between 60 and 94 in./mi., 28% are in acceptable condition with IRI values between 95 and 170 in./mi., and 5% are in poor condition with IRI values of 170 in./mi. or greater. Although Caltrans did not identify which projects included the new specification, a trend was observed that projects completed later had lower IRI values than those completed several years earlier.

Thin Concrete Overlay on Asphalt Pilot Project at Woodland SR 113: Initial Performance

This report presents the initial performance of the Woodland SR 113 thin concrete overlay on asphalt (COA) project built in 2018-2019.The project comprises approximately four miles of a two-lane highway. The COA had 6 ft. transverse joint spacing, a slab thickness of 6in., and an asphalt base that was overall in very poor condition. The performance of the project between the date of construction andOctober 2020 is presented in this report. The performance was evaluated by different means, including periodic visual inspections andlongitudinal profiler evaluations; falling weight deflectometer (FWD) testing; real load testing (RLT), where the concrete strains undertruck loading were recorded; and continuous monitoring of slab temperatures and drying shrinkage deformations. Overall, the projectperformed as expected. Visual inspection of the COA did not indicate any cracking, faulting, or other structural distress. FWD and RLTevaluations indicate that the COA structure has remained stable since the construction. While the smoothness varied considerably during the period evaluated in this report, the variation was caused by changes in slab curvature due to thermal gradients through the slab depthand concrete drying shrinkage.

 Life Cycle Cost Analysis Input Framework for Full Depth Recycling and Application on State Route 113 and State Route 84

Full depth recycling (FDR) has emerged as a feasible rehabilitation alternative in California. This study focuses on addressing the economic feasibility of example FDR structures using life cycle cost analysis (LCCA) that included probabilistic and deterministic life cycle agency costs and deterministic life cycle road user costs. Two LCCA case studies were performed to provide an initial understanding of the agency cost variation. Estimating roadway construction costs plays a key role in pavement LCCA and long-term planning. Materials costs per functional unit are the major input values affecting pavement cost and total construction cost, and they are dependent on project scale, market, region, risk, climate, and economic circumstances. Publicly available contract cost data from past roadway construction activities on the California state highway network were used in this study. Economies of scale suggest that high quantities of materials would have lower unit costs. Unsupervised machine learning techniques were employed to divide the available data into four volume categories (low, medium, high, very high) based on material quantities in a project to accomplish the probabilistic LCCA. Work zone delay road user costs were estimated in RealCost-CA and incorporated into the life cycle cost of each alternative. Case studies were conducted for rehabilitation of two California highways, State Route 113 (SOL 113) and State Route 84 (YOL 84), for a 60-year design life. Two different pavement rehabilitation alternatives were considered for the project, an FDR structure and a hot mix asphalt HMA reconstruction, along with their respective maintenance and rehabilitation sequences. Two different pavement structural design methods were also included in the study to enable comparison: R-value and CalME.

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White Papers (1)

White Paper on Alternate Strategies for Reducing Greenhouse Gas Emissions: A Life Cycle Approach Using a Supply Curve

The purpose of this white paper is to provide Caltrans with a methodology that uses LCA and LCCA analyses to create a “supply curve” that ranks the different strategies/actions that can be taken to reduce GHG emissions and lessen any other environmental impacts that affect ecosystems and human health. For Caltrans to implement the proposed methodology, the process must be validated and assessed using currently available actions. This white paper presents the methodology and demonstrates its initial use in quantifying and ranking several potential strategies.