Development of Safety Performance Measures for Urban Roundabouts in India

[国外交通期刊数据库] 作者:S. Anjana

摘要:Roundabouts, although considered as safe among the various intersection types, have seen an increasing crash rate over the years in India. Geometric design of a roundabout directly influences the driver's speed adoption and maneuvering behavior, and hence plays a vital role in its safety performance. Application of treatments at roundabouts by altering the geometric design requires careful safety evaluation before actual implementation. The present study identified the crash causes and devised safety performance measures for urban roundabouts located in the state of Kerala, India. Crash prediction models and crash modification factors (CMFs) are developed in this study for the safety assessment of geometric design features of roundabouts. Of the many models tried, the zero-inflated negative binomial regression model is the best model to predict the crash frequency of roundabout approaches. Geometric features of the central island, circulatory roadway, and approach roads are associated with the crash occurrence on roundabout approaches. CMFs are developed by a cross-sectional method and are useful for investigating the relationship between safety and geometric design features of roundabouts.

Development of an Electrophoretic Display Technology for Selectively Retroreflective Signs and Pavement Markers

[国外交通期刊数据库] 作者:Christopher Y. Brown

摘要:This paper describes an enabling technology that could be used to develop electronic roadway signs and markers whose display content can be changed and that are selectively retroreflective. This would give them the good visibility of retroreflective signs at night, coupled with invisibility under circumstances where they are not meant to be seen, thereby reducing both confusion and light pollution. This paper describes how the half-silvered and blackened glass beads that constitute the visible components of the display were fabricated in the lab and derives their geometric optics, demonstrating their retroreflective capabilities. The paper also describes the construction of a transparent top electrode necessary to establish the electric field for changing the displays and derives some of the electric properties of the electrode and the resulting capacitorlike display. The work is in an early developmental stage, and the paper concludes with an outline of some of the remaining issues that need to be solved before a working device could be constructed.

Soil Resilient Modulus Regressed from Physical Properties and Influence of Seasonal Variation on Asphalt Pavement Performance

[国外交通期刊数据库] 作者:Changjun Zhou

摘要:Subgrade soil, as the critical underlying support for other pavement layers and traffic loads, should be stiff enough to maintain the integrity of pavement structures and the smoothness of pavement surface. The resilient modulus, as an indicator of subgrade stiffness, is an essential input in the AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG). At input level 1 of MEPDG, the MEPDG generalized model is required to describe resilient modulus of subgrade soil, and the coefficients of this model are used for pavement design. The change of the resilient modulus model has raised the interest of many state highway agencies and made it necessary to convert old resilient modulus test data into new ones required for the MEPDG model. In this study, the coefficients of the generalized and the universal models for soil resilient modulus were obtained through regression of the results of 13 soils in Tennessee. The coefficients of the two models were also compared. There is a potential risk that the coefficients from the universal model may be mistakenly used in the MEPDG instead of those coefficients from the generalized model. The consequence of this improper use was demonstrated in the comparison between the miscalculated and the real resilient moduli. The coefficients of the generalized model were correlated to soil physical properties, which provided an alternate time-saving and economical method to obtain soil resilient modulus as level 2 inputs. The coefficients were obtained at different post-compaction water contents, to allow the estimation of pavement response under seasonal moisture variation of subgrade. Rutting and roughness of two typical pavement sections were analyzed to investigate the influence of the seasonal variation of soil resilient modulus on pavement performance. The results showed that moisture variation had a significant effect on subgrade resilient modulus and, subsequently, on pavement performance. It is recommended that seasonal change in soil resilient modulus be considered in the analysis on pavement performance.

Selection of Preoverlay Repair Methods for Asphalt Overlay on Asphaltic and Composite Pavements in Wisconsin Based on Cost Effectiveness

[国外交通期刊数据库] 作者:Haifang Wen

摘要:Asphalt concrete (AC) overlay is a commonly used rehabilitation technology for existing distressed pavements. Current practice regarding the selection of preoverlay repair is based on the experience of designers and field engineers. Therefore, the performance of asphalt overlays vary significantly. There is a need to develop a guideline to select the most cost-effective preoverlay repair methods. In this study, a database that includes 338 historic asphalt overlay projects is developed. The service lives of the asphalt overlays, based on each preoverlay repair method, are determined. The agency and user costs over the service lives are analyzed. The results indicate that the pavement distress index (PDI) development method based on the regression can be used to predict the service lives of overlays on AC and composite (COMP) pavements (concrete pavement that has been overlaid at least once). For existing AC pavements, milling is recommended when alligator cracking is extensive and no preoverlay repair is needed for other major preoverlay distresses. For existing COMP pavements, milling is recommended regardless of the preoverlay distresses' extent and severity.

Time-Headway Distributions on an Expressway: Case of Bangkok

[国外交通期刊数据库] 作者:Sooksan Panichpapiboon

摘要:Traffic flow modeling is one of the fundamental keys to solving a traffic engineering problem. Among many parameters, time headway is frequently used to model traffic flow characteristics. A statistical analysis of time headways is immensely important to both theoretical traffic modeling and simulation-based traffic modeling. Basically, it allows researchers to describe an inherently random pattern of traffic flows. Past studies have mainly focused on the time headways of vehicles on highways, freeways, and arterials. However, studies of time headways on urban expressways are rather limited and still need further investigation. In this paper, the author investigates and characterizes the time-headway distributions of vehicles traveling on an urban expressway in Bangkok, Thailand. Particularly, the exponential distribution, the lognormal distribution, and the generalized extreme value (GEV) distribution are used to model the time headways. It is found that the GEV distribution is most effective in modeling time headways. In fact, the GEV distribution can describe more than 90％ of the empirical distributions on most lanes and sections of the expressway. On the other hand, the exponential distribution is the least effective distribution. It can only describe the empirical distributions during the periods when the traffic is extremely light.

General Information

[国外交通期刊数据库]

摘要:General Information

Rolling Resistance Measurement and Model Development

[国外交通期刊数据库] 作者:Lasse G. Andersen

摘要:There is an increased focus worldwide on understanding and modeling rolling resistance because reducing the rolling resistance by just a few percent will lead to substantial energy savings. This paper reviews the state of the art of rolling resistance research, focusing on measuring techniques, surface and texture modeling, contact models, tire models, and macro-modeling of rolling resistance.

Risk-Based Planning in Transportation Asset Management: Critical Pitfalls

[国外交通期刊数据库] 作者:Richard Sarpong Boadi

摘要:The 2012 transportation bill, Moving Ahead for Progress in the 21st Century, formalizes the application of risk management in transportation asset management decision making. The bill requires departments of transportation to have a formal risk management plan for the national highway system. When carried out successfully, risk planning can be a very powerful framework to effectively and efficiently manage transportation infrastructure. However, if there is lack of experience with and insight into risk planning, it can go wrong, leading to a counterproductive plan that contributes to ineffectiveness and inefficiencies in the organization and transportation system and to wasted resources. This paper reviews a broad spectrum of literature on risk methods and applications to identify and discuss some common pitfalls-failure to communicate, failure to monitor, proportionality, failure to involve knowledgeable individuals. It synthesizes the results for purposeful use in transportation asset management decision making. The literature review indicates that pitfalls are pervasive and usually familiar to the new generation of industries adopting the principles of risk in their management practices. Accordingly, the paper recommends that decision makers and analysts become more familiar with these pitfalls before embarking on risk implementation programs.

Identification and Prioritization of Critical Transportation Infrastructure: Case Study of Coastal Flooding

[国外交通期刊数据库] 作者:Qing-Chang Lu

摘要:In order to better inform transportation decision makers of the criticality of transportation infrastructure, this paper explores an accessibility-based criticality prioritization methodology to identify and prioritize critical transportation infrastructure. In particular, the methodology evaluates the network-wide impacts of infrastructure degradation based on the increase in travel cost taking origin importance, destination attractiveness, and traffic congestion into account. The methodology is applied to the road network of Hillsborough County, Florida, threatened by flood risk from storm surge, sea-level rise, and intense precipitation. Light detection and ranging digital elevation data, transportation infrastructure and network data, and zone-based population data of the county are processed for analysis. The approach yields results of not only the criticality of transportation infrastructure under flooding impact but also the most vulnerable zones as a result of infrastructure inundation. The results show that some infrastructure is critical to adjacent areas, while some becomes important to a much broader region. The results further demonstrate that the infrastructure is more critical if it serves more people.

Reformulation of the Design Procedure for Aggregate-Surfaced Airfield Pavements

[国外交通期刊数据库] 作者:Alessandra Bianchini

摘要:During military contingency operations, aircraft are required to land, taxi, and takeoff on unpaved surfaces. In some cases, operational time limitations do not allow for the construction of paved surfaces to establish airfield operations. The original flexible pavement design procedure for paved surfaces, which is based on the California Bearing Ratio (CBR) and the α-factor (Alpha-factor), was extended and applied to the design and evaluation of aggregate-surfaced pavements. With the reformulation of the CBR-Alpha for the design of flexible pavements, efforts were also directed at defining a new equation for the design of aggregate-surfaced airfields. This paper focuses on the development of a new CBR-Beta procedure for the design and evaluation of aggregate-surfaced airfields. Data from previous studies conducted on aggregate-surfaced full-scale test sections were used for this purpose. The new performance curve proposed in this paper for aggregate-surfaced airfields has the same format as the equation that was proposed and accepted for flexible pavements.