A box model for North-East Atlantic coastal waters compared with radioactive tracers

A box model for the estimation of doses to members of the public from discharges of radioactivity into North-East Atlantic coastal waters has been used to predict annual means of radionuclide seawater concentrations which have been compared with measured data of tracer radionuclides, ¹³⁷Cs, ⁹⁹Tc and ¹²⁵Sb. Discharges of these radionuclides into the sea from the nuclear reprocessing plants Sellafield in the UK and La Hague in France have been used as input to the model. Fallout of ¹³⁷Cs from atmospheric nuclear weapons tests and fallout of ¹³⁷Cs from the Chernobyl accident into the Baltic Sea have been taken into account. A large proportion of the measured data was collected during the CEC MAST-900052 project which is concerned with the utilization of radionuclides as tracers for water movements. The data cover the time period 1972–1992. A comparison between predicted and measured concentrations of radionuclides in seawater indicated the need to improve the model with respect to mixing conditions in the English Channel and water transport from the North Sea to the Baltic Sea via the Skagerrak, the Kattegat and the Belt Sea. Improvements were made using the data for ¹³⁷Cs and ⁹⁹Tc and involved adjustments of the mixing conditions (water exchange rates) between adjacent water boxes while keeping the net advective water fluxes of the model unaltered. The results of the modified version of the model have been compared with observed values. The comparison shows a somewhat better agreement for ¹³⁷Cs and ¹²⁵Sb than for ⁹⁹Tc which is believed to be due to the lower reliability of the ⁹⁹Tc discharge data from Sellafield in 1978. An analysis of the predicted-to-observed seawater concentrations indicates an overall predictive accuracy of the model of 0.9 corresponding to a 10% underestimation and a predictive precision of about a factor of 2.5 at a confidence level of 95%. The ¹²⁵Sb data, which are independent of the tuning of the model, support the general conclusions about the model predictions of radionuclide concentrations in seawater.     

An inequality between two speed averages

In this note we invoke Schwartz's inequality to relate two speed averages.     

Performance indicator analysis: A management tool for the improvement of bus transit operation in Bangkok

This paper intends to demonstrate that the performance indicator analysis technique can be successfully used as a diagnostic tool to identify operational inefficiency and ineffectiveness at the route level of transit operation. The technique has been applied on 14 bus routes of Bangkok Mass Transit Authority to reveal the inter-route differences in operational efficiency and effectiveness. Twenty performance indicators relating to costs of services, fuel consumption, staff ratio, crew productivity, fleet utilization, service output per bus, daily revenues, etc., were selected to represent the resource efficiency, resource effectiveness and service effectiveness of the bus system. Results of the analyses revealed that considerable variations existed across the routes against many of these 20 selected indicators. These included variations in terms of labor and capacity utilization, maintenance expenditure, etc., many of which can be improved through suitable managerial measures. Based on these findings, specific recommendations have been made for improvement in the deficient areas that are considered to be within the operator domain. These indicators also provide a basis for comparison over time, with other operators and standards. A ranking scale was also developed to determine the over all attractiveness of the routes.     

Estimating bus run times for new limited-stop service using archived AVL and APC data

In recent years, several transit agencies have been trying to be more competitive with the automobile to attract choice riders. Transit agencies can only be competitive if they can provide services that are reliable, have a short access and egress time, and have run times that are comparable to automobiles. Several transit agencies try to be competitive through offering faster service, such as limited-stop (express) bus service. This study uses AVL and APC data, in addition to a disaggregate data obtained from a travel behavior survey, to select stops and estimate run times for a new limited-stop service that will run parallel to a heavily used bus route (67 Saint-Michel) in Montréal, Canada. Three different scenarios are developed based on theory and practice to select stops to be incorporated in the new limited service. The time savings for each scenario are then evaluated as a range and a fourth scenario is developed. A limited-stop service is recommended based on selecting stops serving both directions of the route, major activity points and stop spacing. This study shows that implementing a limited-stop service would yield substantial time savings for both, the new limited service and the existing regular service running in parallel.     

Who can recharge a plug-in electric vehicle at home?

We construct consumer-informed estimates of residential access to vehicle charging to guide understanding of plug-in electric vehicle demand, use, and energy impacts. Using a web-based survey, study 1 estimates that about half of new car-buying US households park at least one vehicle within 25 ft of a Level 1 (110/120 V) electrical outlet at home. Study 2 estimates that just under one-third of new car-buying households in San Diego County have access to Level 2 (220/240 V) charging. Further, 20% of the sample are both able and willing to install Level 2 PEV recharging infrastructure at the prices examined.     

Evaluation of urban accessibility indicators based on internal and external environmental costs

This paper estimates urban accessibility considering types of transport and destinations, taking into account the internal travel time costs, and the ensuing external environmental impacts. Based on online and local surveys, an accessibility function is developed to allow for the construction of an accessibility curve for each transport mode that decreases with distance to represent decaying accessibility. An external environmental impact is associated with the accessibility indicators, taking into account the influence of the cold-start emissions that are particularly relevant for short-distance trips. The methodology is applied to neighborhoods in Lisbon, Portugal, with significant differences in their urban planning, mobility patterns, concentration of services and availability of public transportation.     

Line haul interstation spacing for low cost feeder modes

The choice behaviour of low cost travel (LCT) modes is very sensitive to travel distance. A line haul system designed on the basis of current planning practice of locating widely spaced stations to cater auto and bus feeder modes with the primary objective of gaining travel speed is hostile to non‐motorized and low cost feeder modes. With the revival of interest in promoting the use of walk'n ride and bike'n ride modes, there is a need to develop an appropriate tool to examine the effect of their specific characteristics in establishing the number and location of stations.

A generic normative behavioural hybrid model for locating the cost minimizing number and location of stations is developed for an LCT‐fed line haul system. The model considers the system with many to many two dimensional line haul demand density function in which the density varies in both x‐ and y‐directions. The feeder mode choice behaviour is incorporated in the model by integrating probability‐access/egress distance function with the objective function. Explicit functional relationships among the parameters of these feeder modes such as modal share as a function of access/egress distance with the parameters of line haul systems are developed. Dynamic programming is used to minimize the system cost. The generic model is shown to collapse into several simplified models capable of yielding approximate solutions for several well known special cases. It has been shown that location of stations is sensitive to the through load on board as well as users’ cost that defines the choice behaviour at large. Numerical examples are presented to demonstrate the applicability of the model.     

The choice of ship size on deep-sea general cargo routes †

The introduction of unit load methods, particularly the cellular container system, has been associated with a large increase in ship size on some of the world's major general cargo routes. In this sector, ship size is determined by a set of interactions between handling performance, route length, traffic flow, itinerary, requirements for frequent and regular service, port costs and general system organization. This paper explores these relationships to identify major influences and to consider the prospects for further growth.