TRB Special Report 288: Metropolitan Travel Forecasting: Current Practice and Future Direction identified treatment of nonmotorized travel in regional models as one of eight modeling deficiencies and also as an advanced modeling practice. However, that report and other existing literature provided little information about recent practices. This paper reviews the current practice of incorporation of nonmotorized travel in regional travel demand models in the United States, especially the models of large metropolitan planning organizations developed over the past decade. Overall, some progress with the representation of nonmotorized travel in regional models has been made. This paper discusses and summarizes modeling approaches, including the variables and data used, data issues, and lessons learned; summarizes the major issues and challenges that modelers face when they incorporate nonmotorized travel into regional travel demand models; and makes recommendations for future improvements to models. Recent examples of different approaches to modeling of nonmotorized travel in regional models are also presented. The pros and cons of each approach, including their different data needs and different abilities to evaluate policies and planning scenarios, are discussed. When deciding on the approach that they will take to modeling of nonmotorized travel, agencies need to know the data requirements, model development efforts, and policy sensitivities desired. In the trip-based modeling framework, further enhancements can be made through the use of more refined zone systems and more accurate measurement of variables, although the activity-based modeling approach is more promising. Regardless of the approach taken, targeted and enhanced data on nonmotorized travel and nonmotorized travel infrastructure are greatly needed.
The specification and selection of subsea wellhead systems is typically based on the use of generic system designs which have a defined extreme load capacity. However the fatigue performance of the wellhead system is also a critical aspect of the equipment which may not always be fully evaluated at the specification and selection stage, as the fatigue life is specific to field design parameters. These parameters can include local environmental loading, drilling rig motions, marine riser stackups and BOP configurations, and soil conditions, as well as operational parameters such as riser tensions and mud weights which can vary during different stages of the drilling, completion and work-over operations. This paper will highlight through the use of analytical results the sensitivity of typical wellhead system designs to changes in these design parameters. This will provide an indication of the significance of these parameters on fatigue life predictions for subsea wellhead and conductor systems, and identify scenarios where fatigue is most likely to be of concern.Where fatigue lives are marginal, restrictions on usage such as environmental or connected riser duration limits may need to be imposed for operations. Alternatively fatigue enhancements to the conventional wellhead and conductor system designs and configurations may be required. If identified at an appropriate stage, some of these enhancements can be readily achieved and implemented during the equipment design and manufacture process. This paper shall discuss the potential for the use of these enhancements, identify how best they can be achieved, and show how making these enhancements in the conductor system design can have significant effects on the fatigue life of the wellhead installation. Designing the correct conductor system by determining the fatigue life of a wellhead installation can be critical, whether in shallow water, deep water or in TLP/SPAR applications.
A simple colorimetric procedure was developed for apparent color determinations utilizing platinum‐cobalt standards and expressing the results in Hazen units. The method entails measuring the absorbance of a sample with a colorimeter using two broad band filters; a second absorbance reading is required to obtain a suitable correction for particulates. With this method, the human response factor is minimized, and the precision, as estimated by standard deviation, is one Hazen unit.
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