Nemzetközi szemle: Szeptember
Rugalmas útburkolat felújítás tervezésének javított mechanikai-empirikus stratégiája
Strategy for an Improved Mechanistic-empirical Flexible Pavement Treatment Design
Szerző(k): D. Bodin, G. Jameson
(letölthető ingyenes regisztrációval)
Terjedelem: 80 oldal
This report details research undertaken to improve the mechanistic-empirical procedure for pavement rehabilitation and strengthening treatment design included in Austroads Guide to Pavement Technology Part 5: Pavement Evaluation and Treatment Design. The report describes the research needs and provides a comprehensive roadmap for future work. The project methodology included a gap analysis, a literature review covering the priority areas, and identification of the most appropriate approaches to be further developed for the Austroads rehabilitation design framework for flexible pavements. Two primary areas were identified for future improvements of the mechanistic-empirical thickness design approach: developing processes to characterise past and future fatigue damage of existing bound pavement materials, developing a method to design asphalt overlays against reflective cracking. For the practical application of back-calculation tools, the project also developed a method to evaluate existing back-calculation software.
Követési időköz alapú autóbusz szolgáltatás intelligens közlekedési rendszerei
Intelligent Transportation Systems in Headway-Based Bus Service
Szerző(k): P. Anderson, M.J. Walk, C. Simek
Texas A&M Transportation Institute USA
Terjedelem: 97 oldal
High-frequency bus routes, defined as those with a headway of 10 minutes or less, often experience various operational problems, such as schedule adherence, bunching and gapping, and full load capacity. These problems are particularly severe in high frequency service because passenger arrival patterns and interactions between buses create a positive feedback loop where small variations in bus travel time quickly develop into larger problems if left unchecked. Research has suggested that operating high-frequency routes by headway instead of schedule can improve reliability by focusing on the interactions between buses that drive instability. In headway-based service (HBS), the objective is to maintain consistent and appropriate separation between buses, which requires real-time knowledge of bus locations and some form of communication between buses. Advances in intelligent transportation systems (ITS) have greatly increased the availability of real-time transit data and introduced new means of communications between buses. As a result, many transit agencies in North America and elsewhere have implemented headway-based bus service in the last few years, and others have plans to implement in the future. The purpose of this synthesis was to review the national and peer international state of the practice of headway-based bus service and the proactive use of ITS technologies for monitoring and control. Although ITS technologies have many applications in bus operations, such as collecting ridership data, the focus of this study was on applications that directly support the operation of HBS by helping agencies to monitor buses, anticipate or identify service problems, and implement various operational strategies. The synthesis was conducted in three main phases: a literature review, a survey of North American transit agencies, and case examples of four transit operators.
Aszfalt kötőanyag öregítési módszerek, melyek pontosan jellemzik a keverék öregedését
Asphalt Binder Aging Methods to Accurately Reflect Mixture Aging
Szerző(k): R. Bonaquist, J.J. Adams, D.A. Anderson
Advanced Asphalt Technologies LLC, Western Research Institute, USA
Terjedelem: 244 oldal
This report documents research conducted by the National Cooperative Highway Research Program (NCHRP) to improve laboratory binder conditioning methods to accurately simulate the short-term and long-term aging of asphalt binders, and to calibrate the improved procedures to the aging that occurs during mixture production, transport, and placement as well as during the service life of the pavement structure.
Magas polimer-módosított bitumen tartalmú aszfaltrétegekkel épített útszakaszok laboratóriumi és helyszíni értékelése
Laboratory and Field Performance Evaluation of Pavement Sections With High Polymer-Modified Asphalt Overlays
Szerző(k): J. Habbouche, I. Boz, B.K. Diefenderfer
Virginia Transportation Research Council USA
Terjedelem: 84 oldal
In 2014, researchers at the Virginia Transportation Research Council initiated a study to evaluate the effectiveness of using high polymer-modified (HP) binders in surface asphalt concrete (AC) mixtures. The results were promising enough to support a field study investigating the use of HP binders in asphalt mixtures over jointed concrete pavement. Since 2015, HP AC overlays have been placed at several sections over existing jointed concrete pavement and cracked asphalt pavements in an effort to mitigate reflective cracking. The purpose of this study was to assess the viability of using HP AC mixtures in Virginia as a reflective crack mitigation technique or when deemed appropriate as a tool for increased crack resistance on higher volume facilities. Information on the state of the practice and lessons learned from the use of HP AC mixtures in the United States and Canada are also provided. In general, HP AC mixtures have been used in a wide range of applications under heavy traffic on interstates and slow-braking loads at intersections. No major field-related construction issues in terms of mixing temperatures and in-place compaction of HP AC mixtures were reported and standard construction practices and equipment were used. Good communication between the polymer/binder supplier and the contractor and solid planning prior to the work being conducted were important lessons learned with regard to paving with HP AC mixtures. The performance characteristics of conventional polymer-modified asphalt (PMA) and HP field-produced mixtures were evaluated in the laboratory in terms of durability and resistance to rutting and cracking. Based on the mixtures tested in this study, HP AC mixtures showed better performance when compared with PMA mixtures regardless of the mixture type (dense-graded surface mixtures and stone matrix asphalt [SMA]).
Moreover, SMA mixtures showed better performance when compared with surface mixtures regardless of the asphalt binder type (PMA and HP). Overall, SMA-HP mixtures showed the most promising performance among all evaluated PMA and HP mixtures.
Kerékpározás 50 felett: közelebbi betekintés az idősebb kerékpárosok világába
Cycling Past 50: A Closer Look into the World of Older Cyclists
Szerző(k): C. Kachadoorian
Mineta Transportation Institute USA
Terjedelem: 97 oldal
This document reports on 2,300 responses to a nationwide survey of older adults who cycle. The survey, open from February through September 2020, includes questions about a rider’s cycling history, current cycling habits, and falls. It includes a visual preference survey of various cycling facilities and an online journaling option for two rides subsequent to completing the survey (results of the online journals will be available in the summer 2021). Responses reflect the impact of COVID-19 on older adults’ cycling habits, the impact of aging on ability and agility, the impact of the built environment, types of bicycles, and opportunities to cycle with others. Responses were analyzed by gender and age. Questions such as cycling frequency and falls were compared to a modified version of Geller’s four types of cyclists. Key take-aways include: Many older adults will need to adapt to their changing cycling abilities with a different bicycle, a different expectation about their cycling experience, and local programs to encourage sustained cycling. A fair number of respondents learned to cycle as an adult which suggests that local programs can also encourage older adults to learn to ride and how to select a bicycle. Lower cycling rates may result from not having a bikeable or proper-fitting bicycle, or the money to fix or purchase a bike.
A beépített aszfalt burkolat szabadhézag tartalma és teljesítménye közötti kapcsolat elemzése
Investigating the Relationship of As-Constructed Asphalt Pavement Air Voids to Pavement Performance
Szerző(k): M. Heitzman, C. Rodezno, F. Leiva, F. Gu, G. Elkins, P. Serigos
National Center for Asphalt Technology, Wood Environment & Infrastructure Solutions, Inc. USA
Terjedelem: 209 oldal
The objective of this study was to determine the effect of in-place air voids (AV) on the performance of asphalt concrete (AC) pavements. The research focused on four primary distress types related to asphalt pavement performance: rutting, fatigue cracking, transverse cracking, and ride. The research team applied three analysis methods, common subset scatter plots, regression, and artificial neural networks, to Long-Term Pavement Performance program (LTPP) data and then validated the results with data from other sources. All three analysis methods examined the new construction and pavement rehabilitation LTPP sections as separate groups.
Hálózati szintű makrotextúra mérési előírások
Protocols for Network-Level Macrotexture Measurement
Szerző(k): G.W. Flintsch, E.L. Izeppi, V. Bongioanni, S.W. Katicha, K. Meager, E. Fernando, R. Perera, K.K. McGhee
Virginia Tech Transportation Institute, Texas Transportation Institute, Virginia Transportation Research Council, USA
Terjedelem: 167 oldal
NCHRP Research Report 964: Protocols for Network-Level Macrotexture Measurement provides state transportation pavement engineers and other practitioners with recommended protocols for macrotexture test measures, equipment specifications, and data quality assurance practices. It includes a review of the literature and current practices, as well as equipment comparison experiments and analysis. The report should be of immediate use to pavement and materials engineers and other practitioners responsible for pavement design decisions.
Portland cement beton burkolatok hézag kitöltésének gyakorlata és teljesítménye
Portland Cement Concrete Pavement Joint Sealant Practices and Performance
Szerző(k): J. Kim, D.G. Zollinger
Texas A&M Transportation Institute USA
Terjedelem: 101 oldal
Joints in concrete pavements are intended to provide freedom of slab movement induced by volumetric changes due to drying shrinkage, temperature changes, and moisture differences that develop within the slab. A key purpose for sealing rigid pavement joints should be to prevent or limit the intrusion of an incompressible material and to reduce the amount of water infiltrating the pavement structure (which can result in subbase erosion), loss of support, and other water-related distress. The presence of moisture in a pavement structure contributes to a variety of governing distress types that eventually lead to deterioration of a pavement structure and decreased service life. Recently, the effectiveness of sealants to protect jointed concrete pavement against water-related difficulties has been of great interest. Portland cement concrete (PCC) pavement joint sealing material technology has evolved in recent decades. Some progress in the configuration, design, preparation of sealants, and, in particular, the design and inspection methods of narrow joint widths appears to contradict established recommendations. Although the practice of joint sealing has long been established, the effect of current joint sealant practice has not been well documented. Therefore, it is necessary to establish a standardized approach to joint sealant evaluation as well as to investigate the practice of joint sealant in PCC pavement design.