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As a popular pavement preservation treatment, a slurry seal is typically included in agencies’ maintenance and rehabilitation toolboxes, in decision trees of pavement management systems (PMS), or both. However, performance prediction models for slurry seals are mostly anecdotal or at undertaken at project level. The goal of this paper is to illustrate a method of developing data-driven performance models for slurry seal applications for use at a network level. A total of 537,891 pavement condition records were collected from 18 different agencies in the United States using the Metropolitan Transportation Commission’s PMS program, StreetSaver®. Of these records, 1,195 slurry seal projects met the requirements to be utilized in the development of slurry seal performance models. The development of slurry seal performance models includes grouping project-level modeling results into functional classes, and testing and validating the slurry seal performance models with test cases as well as on actual data produced by agencies. The performance models for slurry seals placed on an asphalt concrete pavement vary depending mainly on the existing pavement’s performance, the timing of the slurry seal application, the functional class, and surface type. The data-driven slurry seal models improved the accuracy of predicting slurry seal performance using PMS. The models could also be used to develop beneficial area curves, which are useful in estimating the cost-effectiveness of slurry seals constructed at various pavement condition index values and in identifying the optimal timings for slurry seal applications at a network level.

This manual presents best practices on project selection, mix design, and construction to ensure a superior product when constructing thin asphalt overlays. Experience shows these treatments provide excellent performance when placed on pavements in fair to good condition using proper construction techniques. Though sometime referred to by other names, thin asphalt overlays have been widely used for pavement preservation throughout the world for over 50 years. Limited infrastructure funding at the local, state, and federal levels has resulted in greater emphasis on the use of pavement preservation techniques to extend pavement life and reduce maintenance costs. Thin asphalt overlays are one of many preventative maintenance treatments. Thin asphalt overlays are placed directly on existing pavement and can range from 1/2 inch to 1 1/2 inches in thickness. Thin asphalt overlays have proven to be an economical means for maintaining and improving the functional condition of an existing pavement since the 1960s. Specifically, this manual provides guidance for engineers regarding where and when to use thin asphalt overlays including: (1) Types and variations of thin overlays; (2) Materials and the design process; (3) Construction; (4) Quality Assurance; and (5) Troubleshooting. This chapter by chapter guidance enables an Agency’s engineers to design and construct a successful thin asphalt overlay project to completion. This manual is one of four new manuals prepared by the California Pavement Preservation Center (CP2Center) using funding from California Senate Bill 1 (SB-1), passed in April 2017. The other three manuals provide detailed design and construction information for (1) chip seals, (2) slurry surfacing, and (3) Cape seals. The creation of these manuals was a task funded entirely from SB-1 monies for the purpose of disseminating training and technical information on highway pavement preservation to local agencies throughout California.

Although rubberized asphalt has more than a 50-year history, it has not been widely adopted due to difficulties with its processability, unstable properties and high initial cost. Chemical approaches, including chemical characterization and the addition of chemical additives to rubberized asphalt, are useful tools to promote the applications of this technology. Chemical characterization techniques such as infrared spectroscopy, thermogravimetric analysis, gel permeation chromatography, and sol-gel analysis are used to analyze the chemical composition of rubberized asphalt. The development of chemical characterization for rubberized asphalt is described in terms of chemical degradation of rubber in asphalt, and stabilization of rubber in asphalt. The evolution of the chemical composition of rubberized asphalt has been evaluated and correlated for dry and wet processing, and indoor and outdoor aging. Following this, high performance rubberized asphalt realized by modification with different chemical additives is also discussed. The additives are categorized into polymers, inorganic filler, plasticizer and others. Finally, methods that combine several types of different additives that can be used to produce rubberized asphalt with stable properties and in an environmentally friendly manner are described.

California Department of Transportation (Caltrans) is interested in preserving the concrete pavement surface from the wear and abrasion of traffic loading. Especially, on a portion of concrete pavement on Interstate Highway 80 near Truckee area where the pavement deteriorates at an accelerated rate due to snow chains and heavy traffic loading in the truck lanes. Historically, Caltrans has tried thin hot mix asphalt overlay, bonded wearing course, rubberized hot mix asphalt overlay, and micro-surfacing as a fix for these wear problems with various levels of success. Currently, Caltrans is looking for new cost effective concrete surface preservation treatments to solve the wear issues. Concrete surface hardeners may offer a less expensive preservation alternative compared to the previous solutions. There were five different concrete surface hardeners from three companies selected for the laboratory study including Transil Plus and Pentra Sil (IH) from Convergent Concrete, Nano-Lithium 25 from Advan, CS and CLS densifiers from Trinic. Three different tests were performed on the treated and untreated cement mortar surfaces. The concrete surface abrasion test, Caltrans Test Method 550, was used to evaluate the surface abrasion resistance of specimens; Mohs hardness test was used to study the surface hardness changes during the surface hardener treatments; and the rebound hammer test, ASTM C805, was used to evaluate the strengths of various treated and untreated specimens. The statistical testing results were calculated and summarized to show the effectiveness of the surface hardeners on various cement types with different water to cement ratios. The test results showed the levels of effectiveness of different concrete surface hardeners had on the various mix designs.

Pavement preservation majorly includes preventive maintenance, routine maintenance, and minor rehabilitation. Pavement preservation has many benefits when utilized correctly including life extension of the existing pavement, low treatment costs, reduced user costs, improved safety and overall network health, etc. A strong preservation program is essential to asset management because it is more cost effective to address minor distresses early, before the defects become major costly problems. Pavement preservation consists of many different kinds of treatments; however, each location has its suitable treatments, particularly in those complex climate environment. Gansu province has various geological and climate conditions, which create challenges to pavement engineering. To find the suitable pavement preservation treatments, a series of pilot testing sections using various pavement preservation technologies have been set up for a long-term pavement performance (LTPP) study. This comprehensive study involves four climate regions (Hexi desert region, Longnan rainy regions, Gannan alpine region and Longdong loess region), six types of general observation sections (Asphalt Concrete, SUPERPAVE, Asphalt Treat Base and so on), and five types of special preservation sections (SPS) (micro-surfacing, cape seal, ultrathin overlay, rubberized asphalt, and Stone mastic asphalt mixture). These test sections are used to help treatment design, strategy selection, and long-term performance modeling of pavement preservation treatments. For the test sections, pavement performance measures, such as pavement distresses, pavement condition index (PCI), Rutting Depth Index (RDI), are observed quarterly each year. To further support the analysis, weather stations have been established to collect temperatures and humidity information for pavements. The collected data are used to determine the influence of different maintenance technologies on pavement performance. The current study results have shown that pavements are more susceptible to crack and rut in the Hexi large temperature variation areas, and the cape seal technology and rubberized asphalt overlay are more suitable for retarding reflective cracking.

The Alaska Department of Transportation and Public Facilities (DOT&PF) wished to enhance its existing pavement preservation management program by using effective pavement preservation treatments for cold regions. This initiative would extend pavement life and defer the need for more costly rehabilitation. By collaborating with the California Pavement Preservation Center and the Alaska University Transportation Center, the Alaska DOT&PF recently completed a pavement preservation research project to improve its pavement preservation program for flexible pavements. Research tasks included conducting an international survey of pavement preservation in cold regions, reviewing literature on cold region pavement preservation treatments, monitoring existing preservation treatments that Alaska used, developing a pavement preservation database, and creating an online computer program for treatment selection. The database for pavement preservation treatment tracking is a web-based online program that includes standard types of pavement preservation strategies used in Alaska; pavement construction, traffic, weather, and other performance-related information; an integrated Google Map function to show the location of pavement preservation projects; and multiple pavement condition survey results with supporting documents. The strategy selection program is integrated within the pavement preservation database. The program sees results of the survey and other information on Alaska treatments to conduct treatment strategy selection and life-cycle cost analysis. Workshops have been given on preservation treatments used in cold regions and use of the database and strategy selection process. Tools developed for the Alaska DOT&PF should be helpful for long-term implementation of an effective pavement preservation program. Other agencies could learn from Alaska's experience.

Successful deployment of transit signal priority (TSP) systems requires thorough laboratory evaluation before field implementation. Traffic simulation is a powerful tool in this regard; however, it requires tremendous efforts toward network coding, data collection, and model calibration. Besides, simulation models tend to be project specific, and the models developed for one project are often discarded upon the completion of that project. In this paper, it is shown that the impacts of two fundamental TSP strategies (early green and extended green) can be evaluated using an analytical approach. The impacts of the above two strategies on both the prioritized and the nonprioritized approaches are illustrated using graphical as well as analytical methods. A simulation study is then conducted for comparison analyses, followed by a statistical approach for the test of generality.

For an actuated signalized intersection, pedestrian calls are likely to affect the effective greens serving the vehicle movements, which affect the capacity and delay of the intersection. However, the current procedure in the Highway Capacity Manual 2000 (HCM) for analyzing actuated signalized intersections treats pedestrian crossing and timing statically, with either pedestrian calls at all signal cycles or no pedestrians at all. In reality, pedestrian arrivals are random events with some cycles having more pedestrians than others and other cycles having no pedestrian call at all. This paper demonstrates that the current procedure can lead to erroneous results in capacity and delay estimations. A model is introduced to overcome the shortcomings in the current procedure. The model takes into account the stochastic nature of pedestrian crossings and their effects. The model computes the probability of having pedestrian calls in a cycle and the corresponding capacities and delays for traffic movements. An implementation framework was developed to help practitioners conduct capacity analyses using the model. The model's results on a semiactuated signal-controlled intersection were comparable with the results from the SimTraffic microsimulation model. The effects of pedestrians on intersection capacity and delay were analyzed using the proposed model. Depending on the pedestrian volume and traffic conditions, the current HCM procedure could produce significant error, especially when the pedestrian volume is low, because it does not consider the stochastic nature of pedestrian arrivals.

Chapter 16 of the Highway Capacity Manual 2000 (HCM 2000) includes models and procedures for calculating capacity and delay at signalized intersections. However, the procedures do not provide estimation of the optimal cycle length which would result in the minimal intersection delay. A quick estimation method for determining the cycle length is described in Appendix A, Chap. 10 of the HCM 2000 for planning level applications. In this method, a simple equation is used to estimate the cycle length if it is not available. However, the estimated cycle length may not be the optimal cycle length from the point of view of achieving minimum intersection delay. To develop a new cycle length model, the Webster's minimum delay cycle length model is first considered. However, based on our study, Webster's minimum delay cycle length model overestimates the optimal cycle length compared to the results from the HCM 2000 delay calculation method, especially under high traffic volume conditions. After investigating three new models developed during this study, an exponential-type cycle length model is recommended. Based on a series of CORSIM simulation runs, the cycle length predicted by this model provides better results than the current quick estimation method of the HCM 2000.

Two moisture damage models based on major moisture failure mechanisms are proposed. The adhesion failure model was developed to analyze the adhesive fracture between asphalt and aggregate in the presence of water. Cohesive and adhesive fractures in an asphalt-aggregate system are directly related to the surface energy characteristics of asphalt and aggregate. The surface energy of adhesion with or without the presence of water can be calculated from the surface energies of asphalt and aggregate. A moisture diffusion model was developed based on the one-dimensional consolidation of soil and a gas adsorption model. The moisture diffusion model was used to obtain the moisture diffusion characteristics of asphalt binders, including the amount of moisture that can permeate a binder and the diffusivity of the binder. The amount of moisture that permeates a binder is identified as a key factor in the moisture damage. Finally, mechanics-based experiments conducted on asphalt mixtures validated the results from the adhesion failure and diffusion models.

Cohesive and adhesive bonding within the asphalt—aggregate system are directly related to the surface energy of the asphalt. The thermodynamic changes in the surface energy of adhesion and cohesion are related to the de-bonding of the interface between asphalt and aggregate and to cracks that may occur within the mastic, respectively. However, it is also true that thermodynamic changes in the surface energy are required to heal a fracture between the surfaces of the asphalt and the aggregate or within the mastic. The methodology and testing protocol for measuring the surface energy of asphalt are presented. Both the surface energy of dewetting (fracture) and the surface energy of wetting (healing) can be obtained from the contact angle measurement with the Wilhelmy plate method. Ten asphalts were tested; surface energies varied substantially as a function of asphalt composition and the level of aging to which the asphalt was subjected. By using thermodynamic theory, the adhesion and cohesion bonding energy within the asphaltaggregate systems were further analyzed. This analysis has the potential to select the most compatible asphalt—aggregate combination for mixtures. The surface energy is also a very important parameter in the fatigue and healing analysis of the asphalt pavement.

Dowel bar retrofit (DBR) is an effective concrete pavement preservation technique to restore the load transfer efficiency at joints of the jointed plain concrete pavement. So far, more than 5 million dowel bars have been installed in the United States. Although the majority of DBR projects were successful, some have had issues, including early failures. Recently, it has been proposed that polyester grout may perform better than conventional DBR grout materials. Polyester grout is a grout using polymerized resin as a binder instead of fast setting concrete backfill material. Compared to conventional grout materials containing high alumina or magnesium phosphate materials, the polyester grout has more flexibility, better adhesion with the existing pavement, and a low viscosity for better consolidation. This paper presents the results of evaluation of performance of US 50 DBR project constructed with polyester grout in 2010 for the California Department of Transportation. In 2012, a team of researchers and engineers conducted visual inspections and nondestructive tests. Core extractions were also performed at a later date based on the visual inspection and non-destructive test results. In the laboratory, the tests included shear bonding strength tests as well as dowel bar pull out tests. The results in both the laboratory and field showed that the polyester grout has worked very well to date.

Quality of pavement condition data is critical to the effectiveness of a pavement management system (PMS). Normally, if there is an error in the pavement condition data, it will affect the prediction of pavement conditions for future years. It may also affect the maintenance and rehabilitation treatment selection strategies and the budgeting and needs estimation at the network level. The Metropolitan Transportation Commission (MTC) of the San Francisco Bay area developed a pavement management program that now has more than 400 users in the United States. To enhance its existing data quality management plan and increase its effective use of pavement management program, MTC implemented a new quality acceptance (QA) program in 2013. This program is expected to significantly improve the quality of the PMS data. The QA program includes (1) developing a Rater Certification Program that ensures good quality data by using certified and trained technicians for the PMS, (2) hiring a third party and neutral institution to audit the various contractors' quality control plan, and (3) verifying the data collected by contractors and checking data collected against pavement deterioration models and curves in the PMS database. The methods used in the MTC's QA program should potentially benefit other agencies that are using pavement management systems.

Pavement preservation can extend a pavement’s effective service life, improve safety and pavement service condition, and is a cost-effective approach. There are many benefits of adding pavement preservation into pavement management system. Pavement management system (PMS) can identify pavement preservation needs and help program pavement preservation projects. Pavement preservation increases the effectiveness of pavement management system, which can allocate available funding more cost-effectively. Although integrating pavement preservation into pavement management system is not a new thing, 9 out of 41 state agencies still utilized "worst first" approaches in their project prioritization based on a survey results in 2008. It is a challenging task to add the pavement preservation component to a PMS. An example of integration of pavement preservation with pavement management system is provided. This paper also provides guidance on how to add the pavement preservation components to pavement management system using a stepwise method.

Pavement preservation treatment selection is a complex process which involves many factors ranging from pavement engineering to economic analysis. To determine the most preferable treatment is very challenging to many pavement engineers, especially for someone with limited experience. Most states or local agencies utilize either decision trees or decision tables to assist with the treatment selection. However, there are some disadvantages of using these decision trees or decision tables. This paper proposes to incorporate the expert system concept into the pavement treatment selection process. The California Department of Transportation (Caltrans) decision tables for treatment selection have been converted to a prototype expert system which includes a user interface, an inference engine, and a knowledge base. The prototype system allows one to evaluate various treatment alternatives. The best alternative based on user provided roadway conditions and weighting scores can then be selected by the expert system. The system can help inexperienced engineers to make a better choice; it can also help streamline the decision making process for seasoned pavement engineers.