Relationship between service quality and demand for inter-urban buses

This article proposes a model for analysing the modal choice of travellers making inter-urban journeys. Discrete choice models with systematic and random tastes variation were applied to find the most relevant variables for encouraging the use of public transport by bus rather than private car. This research follows on from the results of previous user satisfaction studies on inter-urban bus services in the province of Burgos (Spain). Willingness to pay is also estimated for time savings or other improvements in the bus service.The results indicate that, in general, improvements in the journey time or the number of daily journeys are valued less by inter-urban bus users than they are by car or railway users. The type of bus and its characteristics are evaluated as a function of the distance travelled and result in very small values for this variable. Contrary to what is often reported in satisfaction surveys, the journey cost is found to be relevant when choosing which mode of transport to use, but the most important variable is journey time. Little value is placed on the features of the bus, except on long distance journeys.Finally, a methodology differentiating four hierarchical groups is presented for comparing the results of the relevant variables in demand and satisfaction models. Some only improve perception rather than encourage new users, while others increase take-up but do not improve the image of the service.     

Productivity assessment of African seaports with biased technological change

Abstract

This paper analyses the productivity of a representative sample of African seaports from 2002 to 2008. Productivity scores are decomposed, based on the Luenberger productivity indicator, and the nature of technological change is analysed. The paper finds that Nigerian seaports are the most efficient, followed by Angola and Mozambique. Discussions of the results as well as related policy implications are provided.     

Modeling isoexposure to transit users for market potential analysis

Transit operators face a difficult fiscal environment and an imperative to contribute to urban sustainability. Under these circumstances, operators must find innovative ways to make public transportation attractive to broader segments of the public, while simultaneously trying to raise revenue to reduce reliance on public subsidies. Development of commercial partnerships is seen as a promising way to achieve these goals. Previous research has examined the potential of using geodemographics to assist transit agencies in the task of identifying potential partners for developing mutually beneficial commercial agreements. In this paper we describe an approach to model isoexposure to transit users as a tool to assess market potential. The approach is based on the analysis of walking behavior of transit users, and specifically distance walked at the end of their transit trip. Spatial modeling is used to geographically project estimates of walking distance for a desired demographic profile at a specific transit facility. After expanding the estimates using sample weights, overlays of these estimates can be used to generate variations in exposure to transit travelers at different locations in space. The approach is demonstrated using the case of Metro users in Montreal, Canada. The case study demonstrates the use of isoexposure profiles as a novel approach to generate marketing intelligence. This should be of interest to transit agencies and businesses interested in developing partnerships.     

The smoothing effect of carpool lanes on freeway bottlenecks

Real data show that reserving a lane for carpools on congested freeways induces a smoothing effect that is characterized by significantly higher bottleneck discharge flows (capacities) in adjacent lanes. The effect is reproducible across days and freeway sites: it was observed, without exception, in all cases tested. Predicted by an earlier theory, the effect arises because disruptive vehicle lane changing diminishes in the presence of a carpool lane. We therefore conjecture that smoothing can also be induced by other means that would reduce lane changing.The benefits can be large. Queueing analysis shows that the smoothing effect greatly reduces the times spent by people and vehicles in queues. For example, by ignoring the smoothing effect at one of the sites we analyzed one would predict that its carpool lane increased both the people-hours and the vehicle-hours traveled by well over 300%. In reality, the carpool lane reduced both measures due to smoothing. The effect is so significant that even a severely underused carpool lane can in some instances increase a freeway bottleneck’s total discharge flow. This happens for the site we analyzed when carpool demand is as low as 1200 vph.     

Short-sea shipping potentials in Central America to bridge infrastructural gaps

This paper addresses the situation of transport infrastructure in Central America, which poses issues of insufficiency, high-costs and lack of an integrated vision in a geographic region that is exposed to vulnerabilities due to its geological, geomorphologic and climatic conditions. The major efforts for regional integration with joint infrastructure in place seem to meet the criteria of high prioritization on ground transport and non-diversification of risk. This paper features the characteristics of the area and the potentiality of short-sea shipping to cover infrastructure deficits and the need for a more integrated planning of transport infrastructure services with better conditions to improve the regional economy competitiveness and the economic growth.     

Parametric roll mitigation using rudder control

Severe roll angles can be developed by parametric excitation in relatively moderate weather without any apparent pre-warning for the crew onboard. In this study the prospect of using rudder control to mitigate parametric roll was investigated using multi-degree of freedom simulations. A typical modern Pure Car and Truck Carrier was considered and modelled by coupling a roll model with a planar motion manoeuvring model. The combined model was calibrated using in-service, full-scale trials and model tests. Irregular variations of the metacentric height were applied to simulate recorded, full-scale events of parametric roll that have occurred with the considered design. These simulations with rudder roll control showed promising results and demonstrate that the approach could be very efficient for mitigation of parametric roll.     

Heavy metals in edible seaweeds commercialised for human consumption

Though seaweed consumption is growing steadily across Europe, relatively few studies have reported on the quantities of heavy metals they contain and/or their potential effects on the population's health. This study focuses on the first topic and analyses the concentrations of six typical heavy metals (Cd, Pb, Hg, Cu, Zn, total As and inorganic As) in 52 samples from 11 algae-based products commercialised in Spain for direct human consumption (Gelidium spp.; Eisenia bicyclis; Himanthalia elongata; Hizikia fusiforme; Laminaria spp.; Ulva rigida; Chondrus crispus; Porphyra umbilicales and Undaria pinnatifida).Samples were ground, homogenised and quantified by atomic absorption spectrometry (Cu and Zn by flame AAS; Cd, Pb and total As by electrothermal AAS; total mercury by the cold vapour technique; and inorganic As by flame-hydride generation). Accuracy was assessed by participation in periodic QUASIMEME (Quality Assurance of Information in Marine Environmental Monitoring in Europe) and IAEA (International Atomic Energy Agency) intercalibration exercises. To detect any objective differences existing between the seaweeds' metal concentrations, univariate and multivariate studies (principal component analysis, cluster analysis and linear discriminant analysis) were performed. It is concluded that the Hizikia fusiforme samples contained the highest values of total and inorganic As and that most Cd concentrations exceeded the French Legislation. The two harvesting areas (Atlantic and Pacific oceans) were differentiated using both univariate studies (for Cu, total As, Hg and Zn) and a multivariate discriminant function (which includes Zn, Cu and Pb).     

Association of reduced visibility with crash outcomes

Most of the information necessary for driving a vehicle is regarded as visual information. In spite of its importance, visibility conditions at the time of a crash are often not documented at a high level of detail. Past studies have not examined the quantified values of visibility and its association with crashes. The current study merged data collected from the National Oceanic and Atmospheric Administration (NOAA) with 2010–2012 Florida crash data. From the thousands of logged weather events compiled by the NOAA, the researchers isolated periods of normal visibility and comparable periods of reduced visibility in a matched-pairs study. The NOAA data provided real visibility score based on the spatiotemporal data of the crashes. Additionally, the crash data, obtained from Roadway Information Database (RID), contains several geometric and traffic variables that allow for effects of factors and visibility. The study aims to associate crash occurrence under different levels of visibility with factors included in the crash database by developing ordinal logistic regression. The intent is to observe how different visibility conditions contribute to a crash occurrence. The findings indicate that the likelihood of a crash increase during periods of low visibility, despite the tendency for less traffic and for lower speeds to prevail during these times. The findings of this study will add valuable knowledge to the realm of the impact of visibility in the way of using and designing appropriate countermeasures.     

Phytoplankton dynamics related to water mass properties in the Gulf of Gabes: Ecological implications

The spatial distribution of chlorophylls and carotenoids was recorded throughout the Gulf of Gabes (South Ionian Sea) in March 2007, and was related to patterns of the physical structure and the nutrient concentrations.Two distinct water masses were identified based on the temperature and salinity (T–S) analysis: a cool and less salty Modified Atlantic Water (MAW) and a saltier Mediterranean Mixed Water (MMW). There was no significant difference in the mean nitrogen and phosphate concentrations between MMW and MAW, although the silica values were significantly higher in MAW. The Integrated chlorophyll a mean value was about 4 mg m^? 2, with a maximum of 13 mg m^? 2 at MAW stations.Higher Chlorophyll a records in typical MAW stations were mainly due to chlorophytes, which contributed up to 58% of the pigments concentrations in the MAW and about 46% in the MMW. The contribution of chlorophytes to total Chlorophyll a was found to be relatively stable throughout the water column. The contribution of diatoms, which were twofold higher in the MMW than in the MAW, did not exceed 17% of chlorophyll a and was mainly due to subsurface maxima. The chlorophytes, pelagophytes, prymnesiophytes and cryptophytes all together accounted for more than 77% of total chlorophyll a in the MAW and about 67% in the MMW.There were statistically significant differences between MMW and MAW in the pigment contribution of cyanobacteria and pelagophytes. These two taxa accounted for 13% and 24% of chlorophyll a respectively in the MAW and MMW indicating that these differences concerned phytoplankton classes at relatively low contributions to total chlorophyll a.