Effects of household structure and selected travel characteristics on trip chaining

This paper analyzes trip chaining, focusing on how households organize non-work travel. A trip chaining typology is developed using household survey data from Portland, Oregon. Households are organized according to demographic structure, allowing analysis of trip chaining differences among household types. A logit model of the propensity to link non-work trips to the work commute is estimated. A more general model of household allocation of non-work travel among three alternative chain types — work commutes, multi-stop non-work journeys, and unlinked trips — is also developed and estimated. Empirical results indicate that the likelihood of linking work and non-work travel, and the more general organization of non-work travel, varies with respect to household structure and other factors which previous studies have found to be important. The effects of two congestion indicators on trip chaining were mixed: workers who commuted in peak periods were found to have lower propensity to form work/non-work chains, while a more general congestion indicator had no effect on the allocation of non-work trips among alternative chains.     

Inverse Heat Conduction and Data-Type Issues for Advanced Diagnostic Analysis

IlitroductlonNormallytemperaturemeasurementsareusedinaninverseheatconductionanalysis.lnarecelltinverseheatconductioninvestigation[ll,twodatatypes(temperatureandheating/coolingrate)weecomparedforthepurposeofinvestigatingtheireffectonpredictingthesurfaceheatfltixattheprojectedsurface.Itwasillustrated,vianumericalexample,thatthechoiceofinputdatainnuencesbOththeaccurasyandstabilityattheprojectedsurface.Thatis,thepredictionnotonlydePendsonthetemperaturedatabutimplicitlyitsillterpretedheating/cooli…     

Energy Dissipation Due to Vehicle/Track Interaction

The effects of track irregularities and wheel profile on the amount of energy dissipated in railroad freight vehicles is examined. A nonlinear computational model is used to determine the average dissipation in the vehicle suspension and the wheel/rail contact patches. This dissipation is a component of the total resistance force acting on the vehicle. Parametric results are presented showing the effects of track geometry, wheel profile, suspension design, and hunting on train resistance. Track geometry studies consider the effects of track quality and curving. The AAR 1:20 wheel profile and the Heumann wheel profile are compared under various operating conditions. Compared with the Heumann profile, the AAR 1:20 profile is shown to have lower average resistance on good quality tangent track, but higher average resistance in steady curves. A trade-off exists between the two profiles when dynamic curve entry is considered.     

A novel semi-empirical tyre model for combined slips

A new tyre-force model for simultaneous braking and cornering is presented, which is based on combining existing empirical models for pure braking and cornering with brush-model tyre mechanics. The aim is to offer an easy-to-use, accurate model for vehicle-handling simulations. On a working tyre the contact patch between the tyre and the road is, in general, divided into an adhesion region where the rubber is gripping the road and a sliding region where the rubber slides on the road surface. The total force generated by the tyre is then composed of components from these two regions. The brush model describes this in a mechanical framework. The proposed model is based on a new method to extract adhesion and sliding forces from empirical pure-slip tyre models. These forces are then scaled to account for the combined-slip condition. The combined-slip self-aligning torque is also described. A particular feature of the model is the inclusion of velocity dependence, even if this is not explicitly present in the empirical pure-slip model. The approach is quite different from most previous combined-slip models, in that it is based on a rather detailed mechanical model in combination with empirical pure-slip models. The model is computationally sound and efficient and does not rely on any additional parameters that depend on combined-slip data for calibration. It can be used in combination with virtually any empirical pure-slip model and in this work the Magic Formula is used in examples. Results show good correspondence with experimental data.     

Pole location control design of an active suspension system with uncertain parameters

This paper addresses the problem of robust control design for an active suspension quarter-car model by means of state feedback gains. Specifically, the design of controllers that assure robust pole location of the closed-loop system inside a circular region on the left-hand side of complex plane is investigated. Three sufficient conditions for the existence of a robust stabilizing state feedback gain are presented as linear matrix inequalities: (i) the quadratic stability based gain; (ii) a recently published condition that uses an augmented space and has been here modified to cope with the pole location specification; (iii) a condition that uses an extended number of equations and yields a parameter-dependent state feedback gain. Unlike other parameter-dependent strategies, neither extensive gridding nor approximations are needed. In the suspension model, the sprung mass, the damper coefficient and the spring constant are considered as uncertain parameters belonging to a known interval (polytope type uncertainty). It is shown that the parameter-dependent gain proposed allows one to impose the closed-loop system pole locations that in some situations cannot be obtained with constant feedback gains.     

Annual uptake of atmospheric CO2 by the Weddell Sea derived from a surface layer balance, including estimations of entrainment and new production

Data from two cruises, one in April/May 1996 and one in December/January 1993, covering the same wide area in the offshore Weddell Sea, were used to derive the annual extent of entrainment and the capacity of the biological pump. The former property was obtained with the help of dissolved oxygen data, whereas the latter was approximated with nutrients. Especially the data from April/May, representing the initial state of the winter surface layer, were crucial to assess the annual extent of these processes. The results were applied to our carbon dioxide data. The annual increase of the Total CO₂ (TCO₂) concentration in the surface layer due to vertical transport amounts to 16.3 μmol kg⁻¹. An entrainment rate of deep water in the surface layer amounting to 35±10 m yr⁻¹ was deduced. The compensating, biologically mediated TCO₂ reduction was calculated to be larger than the TCO₂ increase due to vertical transport. Since the balance of these two processes determines whether the Weddell Sea is a source or a sink of CO₂, this indicates that the Weddell Sea, albeit upwelling area, is definitely a sink for atmospheric CO₂ on an annual basis. This conclusion is further supported by contemplations that the biological drawdown of CO₂ in the Weddell Sea as a whole is probably underestimated by our calculations. The new production for the Weddell Sea on a per unit area basis was found to be much higher than that for the Antarctic Ocean, when the latter value is being obtained by traditional biological methods. On the other hand, the CO₂ uptake by the Weddell Sea on a per unit area basis is somewhat smaller than the CO₂ uptake by the world ocean.     

Pantograph/Catenary Dynamics and Control

The pantograph-catenary system with its dynamic behaviour turned out to be a crucial component for new train systems required to run at higher speeds. With the present systems, operational limitations have to be accepted when running with several pantographs in the train set, when tilting trains are employed, when running on low quality catenary sections or when stricter noise reduction regulations are forcing lower noise emissions also for the pantographs. This paper gives an overview of the methods to describe the catenary and the pantograph system dynamics. Furthermore, aspects concerning the interaction between current collectors and overhead equipment, the acquisition of the model data and the verification are presented. Finally various constructions of passive pantographs and proposals for active control concepts are discussed.     

Some New Results in Rolling Contact

In the present paper three problems in the simplified theory of rolling contact are investigated. As to the first problem, three benchmark loadings, derived by Kalker in 1973 for Hertzian rollingcontact, are in existence. Each of these loadings gives rise to a value of the flexibility parameter of the simplified theory. These values are combined to a single, creepage dependent value of the flexibility, which appears to have an error of at most 10 to 15%. Secondly, the law of Coulomb is generalised by introducing two values of the coefficient of friction. The FASTSIM algorithm is adapted to that, and it is found that the traction, and hence the displacement, show a discontinuity inside the contact area. The discontinuity in the displacement is removed by introducing damping in the constitutive relations of the simplified theory. The damping constant is determined experimentally. When the damping coefficient decreases, the damped solution tends to the solution obtained directly without damping. This establishes the correctness of the latter, but it does not compare well with the complete theory as implemented by the program CONTACT. Thirdly and finally, it is shown that inertial effects may be neglected at speeds of around 100 km/h and also for much higher rolling velocities.     

Cost-benefit analysis,government policy and the British railway network

In 1963 the Beeching Report on Britain's railways proposed the closure of a substantial part of the railway network (British Railways Board, 1963). Although many services were withdrawn, disquiet at the Report's failure to analyse the social benefits of rail passenger services eventually led to the application of the technique of cost-benefit analysis to the problem of unremunerative rail services. However, although such studies revealed that the retention of many rural rail services could not be justified on social grounds, these services were not withdrawn. This paper outlines briefly the history of attempts to deal with the question of the optimal size of the rail passenger network. Secondly, it considers the social cost-benefit case for reducing the present size of the network in Britain and the quantifiable benefits from such a reduction. The problem of joint costs is discussed. Finally, it attempts to explain the failure of successive Governments to apply the results of cost-benefit studies in practice, and suggests how the decision-making process might be altered to facilitate a more rational approach towards public transport problems in Britain.     

Environmental traffic management — The end of the road?

This paper questions some aspects of the technical soundness and public acceptability of environmental traffic management scheme of the kind advocated in the Buchanan report, Traffic in Towns. Practical studies have shown that in inner city areas in particular, and perhaps older built-up areas in general, the concept cannot be adequately defended against a wealth of variety of criticism from those whom it most directly affects, i.e. the public. Participation exercises have revealed public fears that the road closures associated with schemes will ruin the viability of local shops, worsen the environmental conditions along local roads chosen as distributors, cause even greater congestion on the main road network due to displaced traffic, and impede the accessibility of local people to their homes. In the light of these, it is suggested a flexible policy be adopted incorporating changes to the forms of vehicles and the manner in which they are used as well as changes to the physical form of the road network.The opinions expressed in this paper do not necessarily reflect those of the organisations to which the authors are attached.