Trip generation modeling using data collected in single and repeated cross‐sectional surveys

The majority of US metropolitan regions still use the four‐step urban transportation modeling system to develop their travel forecasts. Trip generation, the first step of this system, has as objective of predicting the expected total travel demand in a region. The commonly used methods in planning practice for predicting this expected total travel demand typically use only the most recent cross‐sectional data available from a study region for model development, which ties the resulting travel‐forecast model to the economic environment prevailing at the time of data collection. Applying such models to generate forecasts of travel in economic environments significantly different from those embodied in the estimated model parameters could result in greater errors than would otherwise be the case. To address the aforementioned problem, this paper proposes the development of trip generation models estimated on multiple independent cross‐sectional datasets collected in the same urban region but at different times representing different economic environments. Data used in the research were collected in cross‐sectional household travel behavior surveys undertaken in the Greater Toronto Area, Canada in 1986, 1996, 2001, and 2006. The results lead to the conclusion that well‐specified models, estimated on pooled multiple cross‐sectional datasets, yield travel predictions in the base and horizon years, respectively, that have smaller error compared with corresponding travel predictions generated with single cross‐sectional models. Copyright © 2012 John Wiley & Sons, Ltd.     

Re-evaluation of the widely applied force-frequency relation for frequency-modulation AFM under solution

Frequency-modulation atomic force microscopy （FM-AFM） is a highly versatile tool for surface science. Besides imaging surfaces, FM-AFM is capable of measuring interactions between the AFM probe and the surface with high sensitivity, which can provide chemical information at sub-nanometer resolution. This is achieved by deconvoluting the frequency shift, which is directly measured in experiments, into the force between the probe and sample. At present, the widely used method to perform this deconvolution has been shown to be accurate under high quality （high-Q） factor vacuum conditions. However, under low quality （low-Q） factor conditions, such as in solution, it is not clear if this method is valid. A previous study apparently verified this relation for experiments in solution by comparing the force calculated by this equation with that obtained in separate experiments using the surface force apparatus （SFA）. Here we show that, in solution, a more direct comparison of the force calculated by this relation with that directly measured by the cantilever deflection in AFM reveals significant differences, both qualitative and quantitative. However, we also find that there are complications that hinder this comparison. Namely, while contact with the surface is clear in the direct measurements （including the SFA data）, it is less certain in the FM-AFM case. Hence, it is not clear if the two methods are measuring the same tip-sample distance regimes. Thus, our results suggest that a more thorough verification of this relation is required, as application of this formulation for experiments in solution may not be valid.     

Port competitiveness in container traffic from an internal point of view: the experience of the Port of Algeciras Bay

The objective of this article is to analyse the factors that affect port competitiveness from the perspective of the agents and companies that operate in one of the Mediterranean ports most active in container traffic: the Port of Algeciras Bay (PAB). It is essential to understand the perspective of the suppliers of port services, in order to apply the necessary judgment when formulating policies to strengthen the competitive position of a port. The model selected to meet the objective outlined is based on the 'extended diamond' of Porter. The universe for the study comprises all the institutions and companies involved in the containerization process in the Port of Algeciras Bay. Within this methodology, two procedures are utilised. First, from the quantitative perspective, a survey has been conducted to obtain responses to two groups of questions, one dealing with situation and the other with perceptions. Second, and from a qualitative perspective, several open interviews have been conducted to corroborate the responses obtained to the questionnaire. From the data obtained in the survey, a model has been estimated that minimises the sum of the residuals in absolute value, utilizing the L1 regression; this model enables the competitive advantages and disadvantages of the PAB, from the point of view of the port operators, to be determined by an analysis of residuals. This analysis demonstrates that the variables representing greater competitive advantages are associated with trans-shipment, and with the maritime accessibility of the Port to vessels, whereas those generating greater disadvantages are associated with rail transport (which, according to those surveyed, has resulted in the diversion of significant volumes of traffic to other Spanish or European ports with better communications, particularly Valencia, Barcelona and Gioia-Tauro, and with the state of competition in container trans-shipment activities.     

Spatial and temporal variation of bacterioplankton in a sub-Antarctic coastal area (Kerguelen Archipelago)

Bacterial abundance and production were measured monthly for one year along cross-shore transects in 3 sub-Antarctic fjords of the Kerguelen Archipelago (seven stations each). Mean values of the 3 most coastal (inside) and most offshore (outside) stations were used to describe the relationship between temperature, phytoplankton biomass, bacterial abundance and bacterial production over a one year annual cycle. The entire sampling protocol was repeated twice during each cruise: once at noon and once at midnight. Over the whole sampling period, the temperature ranged from 2.1 to 7.4 °C, while chlorophyll a concentrations varied by a factor of 10, and bacterial abundance and production varied by factors of 12 and 30, respectively. Within one day, all of these parameters sometimes varied by a factor of 4 between noon and midnight. A clear seasonality was observed for all of the parameters. However, while variations of phytoplankton and bacterial production paralleled those of temperature, bacterial abundance was low in midsummer and maximum in autumn. While no general pattern could be observed from the total data set, spatial gradients could interfere strongly with temporal changes.     

Introducing change to transportation and energy systems: the case of alcohol fuels

This paper describes the application of optimization techniques to the problems of garage location and bus routing. The technique employed involves the decomposition of a garage location and bus routing model into two submodels. Solutions for the garage location and bus routing submodels are combined iteratively to find an optimal solution for the overall optimization model. Significant cost savings realizable for the Transit Authority of River City (Louisville, Kentucky) were calculated by implementing the results.     

A system for determining economic loss associated with estuary degradation

Abstract

This article suggests a method of estimating economic losses for estuary‐dependent faunal species under conditions whereby the impact of a given degrading development on a particular estuary has a significant degree of uncertainty associated with it. The approach draws on standard theories from a variety of disciplines to provide an operational procedure capable of joint application by biologists, economists, and other related disciplines with working responsibility in the subject area. Consideration is given to probability estimation of possible impacts, sensitivity to underlying assumptions, and decisional safety under conditions of uncertainty. Applied results are demonstrated in a simulation of a negative developmental impact on the estuary‐dependent salmon resources of the Fraser River in British Columbia.     

Greenhouse gas mitigation supply curve for the United States for transport versus other sectors

To compare transportation greenhouse gas mitigation options with other sectors, we construct greenhouse gas mitigation supply curves of near-term technologies for all the major sectors of the US economy. Our findings indicate that motor vehicles and fuels are attractive candidates for reducing GHGs in the near and medium term. Transport technologies and fuels represent about half of the GHG mitigation options that have net-positive benefits – so-called “no regrets” strategies – and about 20% of the most cost-effective options to reduce GHGs to 10% below 1990 levels by 2030.     

Impact of proposed federal limits on US bagged food aid shipments: reduction in MSF carrier profits—a risk assessment 1

This paper is a stochastic risk simulation of the impact of proposed federal tonnage limits on US Maritime Security Fleet (MSF) bagged food aid shipments. Only MSF (i.e. federally subsidized carriers/vessels for war, or emergencies) and non-MSF US carriers (therefore, at competitive disadvantage) can compete for such shipments—representing an indirect subsidy to both groups. To compensate, US Congress proposed a financial penalty (loss of voyage subsidy) on MSF carriers for food aid above a certain limit. Accordingly, certain carriers will be policy 'winners' (non-MSF—larger food aid shipments), and others 'losers' (MSF). By simulating loss-minimizing economic behaviour by MSF carriers—using five stochastic factors—I obtain losses substantially below those claimed by the MSF owners.

Simulated annual-average MSF profits reduction is $3.5 million—within a large confidence interval; if no carriers surrender their subsidies (as claimed by MSF owners), a reduction of $6.0 million. Only 16% of annual MSF voyages are affected by a 2,500-ton limit (3%; 5,000-ton limit). Minimizing losses, 25 (of 41 affected) annual MSF voyages replace 38,000 tons of food aid with 23,000 tons of other cargo—forgoing $2.1 million in yearly direct subsidies. Two assumptions explain most of this simulated loss reduction.     

Impact of interviewing by proxy in travel survey conducted by telephone

Telephone‐interview surveys are a very efficient way of conducting large‐scale travel surveys. Recent advancements in computer technology have made it possible to improve upon the quality of data collected by telephone surveys through computerization of the entire sample‐control process, and through the direct recording of the collected data into a computer. Notwithstanding these technological advancements, potential sources of bias still exist, including the reliance on an adult member of the household to report the travel information of other household members. Travel data collected in a recent telephone interview survey in the Toronto region is used to examine this issue. The statistical tool used in the research was the Analysis of Variance (ANOVA) technique as implemented within the general linear model framework in SAS. The study‐results indicate that reliance on informants to provide travel information for non‐informant members of their respective households led to the underreporting of some categories of trips. These underreported trip categories were primarily segments of home‐based discretionary trips, and non home‐based trips. Since these latter two categories of trips are made primarily outside the morning peak period, estimated factors to adjust for their underreporting were time‐period sensitive. Further, the number of vehicles available to the household, gender, and driver license status respectively were also found to be strongly associated with the underreporting of trips and thus were important considerations in the determination of adjustment factors. Work and school trips were found not to be underreported, a not surprising result giving the almost daily repetitiveness of trips made for these purposes and hence the ability of the informant to provide relatively more precise information on them.     

Active Suspension Control to Improve Vehicle Ride and Handling

In practice most active vehicle suspension work can be traced to two sources, Lotus' modal control and Karnopp's skyhook damper. A model is developed which allows comparison of different active suspension control algorithms. The Lotus modal control algorithm is reviewed, and compared with Karnopp's skyhook damper. It is shown that a tight inner closed loop allows the Lotus algorithm to achieve the inertial damping described by Kamopp for a single comer or quarter car. It is suggested that to achieve simultaneously high inertial damping and good disturbance rejection an inner force loop is desirable. A vehicle control scheme is presented which combines the Lotus modal decomposition with Karnopp's skyhook damper, allowing nearly optimal ride and simultaneously permitting modification of vehicle handling properties.