Analyzing the structure of informal transit: The evening commute problem

Through the use of a profit-maximizing continuum approximation model, this paper systematically analyzes the development and structure of informal transit systems as a function of the network, user, and modal characteristics. This study examines the evening commute problem along a linear corridor where passengers originate uniformly from a central business district and have destinations uniformly distributed along the corridor. Informal transit drivers who are profit-maximizing will be compared against the traditional case of coordinated, government service that aims to maximize the total welfare. Policies, such as fare regulation and vehicle licensing schemes, will be presented to help rationalize informal transit service using a government-operated service as the baseline.     

Linear probit models: Statistical properties and improved estimation methods

The multinomial probit model is a statistical tool that is well suited to analyze some transportation problems. Modal split, gap acceptance, and route choice are some examples of application contexts. This paper presents an in-depth analysis of its statistical properties and an estimation method for the trinomial case. In the statistical part of the paper it is shown that for multinomial probit models with specifications that are linear in the parameters, the global maximum of the log-likelihood function is consistent if the data do not exhibit multicollinearity as defined in the text. For the special case with three alternatives, lack of multicollinearity is also shown to guarantee asymptotic efficiency and normality, and the uniqueness of any root of the likelihood equations. In addition, it is also shown that for the trinomial probit model certain goodness-of-it measures and test statistics can be easily calculated. The methods part of the paper introduces an estimation process that solves the likelihood equations using a special purpose table of the bivariate normal distribution and analytical derivatives of the log-likelihood function. The method is very accurate, can be applied to nonlinear specifications, and is considerably faster than current computer programs. For linear specifications, the method can be mathematically proven to converge if the log-likelihood equations have a root.     

Determinants and consequences of rapid growth in the Brazilian shipbuilding industry

In this paper a qualitative approach is taken to assess the influence of certain factors upon the direction of economic growth and the levels of technological development achieved by the Brazilian shipbuilding industry since 1958. Its shows that technological maturation can be a lengthy, uneven and costly process. Absolute and significant growth was achieved whereas only a heterogeneous technological base has been developed. It is suggested that three interrelated factors, all evolving dynamically through the years, have influenced this apparently contradictory state of affairs: the mode of State support, the growth and technological strategies of individual firms, and the product of the technology transfer process.     

Estimation of gap acceptance parameters within and across the population from direct roadside observation

This paper explores the feasibility of maximum likelihood as an approach to determine the parameters of gap acceptance functions when these functions vary from individual to individual. Specifically, it is shown that it is theoretically possible to estimate the average critical gap of a population of drivers (or pedestrians) and its variance, within and across individuals, from direct roadside observations. Although the Multinomial Probit Model provides a natural theoretical framework for the estimation of these parameters, the model seems not to be statistically estimable for this particular problem. It was shown, however, that if one of the parameters is known, the other two become estimable and a two-stage estimation process that takes into account this phenomenon can be utilized. The technique is demonstrated with the 203-driver data set included in Appendix A. The Multinomial Probit Model can also be used to determine simultaneously the mean critical gap, the mean critical lag (the first gap considered by a driver), and the variances of these. For the data set in Appendix A, the mean critical gap was significantly smaller than the mean critical lag, as one might expect. The techniques proposed in this paper have the further advantage of being statistically efficient with large data sets and of not requiring a panel of individuals to be observed under controlled conditions.     

Synthesis of experimental designs of maneuvering captive-model tests with a large number of factors

An approach to synthesizing D-optimized experimental designs for an arbitrary number of factors was developed and tested on a third-order polynomial regression model with 5–8 factors. Three options were envisaged for the internal optimization procedure: an exhaustive search, a quasirandom search with the help of the Sobol sequences, and a genetic algorithm. The calculations performed have shown the pronounced superiority of the variant involving a genetic algorithm. Captive-model tests with a catamaran model with varying Froude number, drift angle, rate of yaw, sinkage, trim, and heel are presented as an example of the practical synthesis of the experimental design. The linear regression model constructed is a third-order 5-factor polynomial with respect to all factors except the Froude number. The influence of the latter is accounted for by representing the polynomials regression coefficients as functions of the Froude number represented as a truncated Fourier series with a linear term added.     

Supplying a single location from heterogeneous sources

This paper studies how items with different characteristics, and being demanded at different rates from a finite number of supply points, should be transported to a common destination. The items may differ in size and value, and the origins may differ in their spatial distribution, the kind of items they produce and the production rate. Depending on the application context, the common destination can represent a warehouse, a factory, a military base, a break-bulk terminal, a port or another kind of transportation terminal. Different kinds of items may call for separate transportation treatment if, for example, the items have sharply different inventory carrying costs or their origins are not equally scattered. On the other hand, if their characteristics are not very different, they may be transported together more cheaply because of existing economies of scale. In fact, in most applications it should be optimal to use only a few transportation systems because the economies of scale are quite strong. The paper essentially shows that origins can be ranked according to a simple criterion, and that if two origins are served together, the ones ranked in between should be served with them. A simple method for determining the optimal number of transportation systems and the sources served by each is developed. The technique is illustrated with a numerical example. The results of the paper are developed assuming that supply points do not cluster together by type and that the density of suppliers is slowly varying. In any practical application in which these assumptions are not reasonable approximations, the results of this paper should not be applied too literally. Nevertheless, they can still be used as guidelines in the search for an optimum supply strategy.     

Physical distribution from a warehouse: Vehicle coverage and inventory levels

This paper studies the costs involved in distributing items from a warehouse or depot to randomly scattered customers on a day-to-day basis. Two trade-offs are explored simultaneously. The first one arises because by accumulating large inventories at the depot it is possible to build more efficient distribution tours. This trade-off has already been explored for both distribution of goods (Burns et al., 1983) and passengers (Daganzo et al., 1977; Hendrickson, 1978). Another tradeoff, which involves the length of individual vehicle tours (Clarens and Hurdle, 1975), balances the inventory inside the vehicles against the transportation cost. Banks et al. (1982) have considered both of these tradeoffs simultaneously in the context of passenger transportation, but used a somewhat unrealistic model for vehicle routing. This paper is similar to the latter reference but uses a different routing strategy. It also illustrates how the nature of the objects carried (cheap goods, expensive goods, people, etc.) affects the optimal configuration of the distribution system and the overall distribution costs. Usually there is an optimum partitioning of the service area into districts and an optimum dispatching frequency in each district. The results can vary tremendously, depending on factors such as: the inventory carrying cost per item per unit time, the transportation costs, the demand per unit area and unit time, the average distance from the depot, the average vehicle speed and the time per stop.As an illustration of the ideas, a hypothetical limousine service from an airport is analyzed. The example is used to demonstrate how dramatically the optimal system configuration depends on the nature of the items carried.     

Workshop 2: Bus rapid transit as part of enhanced service provision

Workshop 2 focused on the role of BRT as part of enhanced public transport service provision. Discussion topics included case studies around the world; improved performance and operations; and better contracts, institutional settings and enhanced policies. BRT was identified as a vital component of modern public transport systems due to its ability to provide high performance and rapid implementation at a lower cost than comparable rail transit. The participants concluded that on top of improving trunk transit corridors, it is important to look to the first and last kilometers and the connections among transport modes. In addition, it is important to consider all dimensions, not just the technical issues. The workshop identified the desirable ingredients for BRT success, created a table of bus based options for different applications and a list of research topics.     

Real-time vision-based blind spot warning system: Experiments with motorcycles in daytime/nighttime conditions

This paper describes a real-time vision-based blind spot warning system that has been specially designed for motorcycles detection in both daytime and nighttime conditions. Motorcycles are fast moving and small vehicles that frequently remain unseen to other drivers, mainly in the blind-spot area. In fact, although in recent years the number of fatal accidents has decreased overall, motorcycle accidents have increased by 20%. The risks are primarily linked to the inner characteristics of this mode of travel: motorcycles are fast moving vehicles, light, unstable and fragile. These features make the motorcycle detection problem a difficult but challenging task to be solved from the computer vision point of view. In this paper we present a daytime and nighttime vision-based motorcycle and car detection system in the blind spot area using a single camera installed on the side mirror. On the one hand, daytime vehicle detection is carried out using optical flow features and Support Vector Machine-based (SVM) classification. On the other hand, nighttime vehicle detection is based on head lights detection. The proposed system warns the driver about the presence of vehicles in the blind area, including information about the position and the type of vehicle. Extensive experiments have been carried out in 172 minutes of sequences recorded in real traffic scenarios in both daytime and nighttime conditions, in the context of the Valencia MotoGP Grand Prix 2009.     

LUTI operational models review based on the proposition of an a priori ALUTI conceptual model

ABSTRACT

This paper focuses on understanding to what extent the components of LUTI models and their mutual interactions are conceptually represented by eight operational LUTI models. This is important for the understanding of LUTI models’ mechanisms, firstly because it may reduce communication barriers between planning communities, secondly because it may help us understand the models’ applicability, and thirdly it may highlight the models’ shortcomings and point for future research. We present a discussion about what subsystems should be considered for LUTI modelling, from which we derived an “a priori” conceptual ALUTI model (incorporating Activities, besides Land Use and Transport). By comparing the rationale behind each model with this conceptual model, we establish the basis for our review, focussing on whether these models incorporate the ALUTI components, its inner workings and the relationships between these components. Results indicate three main limitations of the reviewed models. First, models not always adequately include all the components of the a priori ALUTI model. Second, the ALUTI subsystems’ internal functions are not explicitly modelled in several of the models reviewed, making it difficult to evaluate how planning decisions affect the subsystem. Third, only few models recognise all mutual interactions, especially in respect to the Activity subsystem.