Transport demand model estimation from traffic counts

Many problems in transport planning and management tasks require an origindestination (O-D) matrix to represent the travel pattern. However, O-D matrices obtained through a large scale survey such as home or roadside interviews, tend to be costly, labour intensive and time disruptive to trip makers. Therefore, the use of low cost and easily available data is particularly attractive.The need of low-cost methods to estimate current and future O-D matrices is even more valuable in developing countries because of the rapid changes in population, economic activity and land use. Models of transport demand have been used for many years to synthesize O-D matrices in study areas. A typical example of this is the gravity model; its functional form, plus the appropriate values for the parameters involved, is employed to produce acceptable matrices representing trip making behaviour for many trip purposes and time periods.The work reported in this paper has combined the advantages of acceptable travel demand models with the low cost and availability of traffic counts. Three types of demand models have been used: gravity (GR), opportunity (OP) and gravity-opportunity (GO) models. Three estimation methods have been developed to calibrate these models from traffic counts, namely: non-linear-least-squares (NLLS), weighted-non-linear-least-squares (WNLLS) and maximumlikelihood (ML).The 1978 Ripon (urban vehicle movement) survey was used to test these methods. They were found to perform satisfactorily since each calibrated model reproduced the observed O-D matrix fairly closely. The tests were carried out using two assignment techniques, all-or-nothing and the stochastic method due to Burrell, in determining the routes taken through the network.requests for offprints     

Estimating intersection O-D matrices from observed time-series of traffic counts: The zellner estimator

The problem of estimating intersection O-D matrices from input and output time-series of traffic counts is considered in this paper. Because of possible existence of significant correlation between the error terms across structural equations forming the O-D matrices, the seemingly unrelated estimator (Zellner estimator) was suggested. Estimation results showed evidence of strong correlation between error terms across-equations. Generally, the Zellner estimator produced more efficient estimates than did the ordinary least-squares estimator. Furthermore, the Zellner estimator satisfied all constraints and reproduced turning movements comparable to the actual ones.     

Container shipping in 1990

By 1990 express shuttle container ships will dominate the USA/North European and USA/Pacific trades. The pattern is already apparent in the Pacific. These will touch only a few ports such as Halifax, New York and Virginia on the Atlantic and Los Angeles/Long Beach, Oakland and Seattle/Tacoma in the West. Their low costs and good services will capture over 80% of available general cargo. Round the world systems will be left with lucrative fringe business in the Mediterranean, US Gulf/South Atlantic, Singapore, India and Arab countries.

Progress will be sensitive to twelve trends. Most important of these will be labour resistance and management concerns about rapid obsolescence of ships and terminals. Rail and ship costs have been rationalized and are not as flexible as terminal costs. The ultimate terminal will consume about one third of the time and money presently needed.

This paper is chiefly intended to suggest a forecasting methodology.     

Forecasting telecommuting

Transportation planners increasingly recognize telecommuting as an important trend. But while they often advocate telecommuting as a transportation demand management strategy, transportation planners have made little progress toward incorporating telecommuting into transportation forecasts, at least partly because of the limited data available. In this paper we explore four alternative methodologies for forecasting telecommuting and discuss the kinds of data that must be collected before these methodologies can be applied. The first approach is trend extrapolation, using curves of technological substitution. Sufficient data are currently available to produce forecasts, albeit highly uncertain forecasts, using this approach. However, even with better data this approach does not address underlying factors and trends that will affect the future of telecommuting. As a result, we explore three additional approaches that should produce more reliable forecasts but which require new data and knowledge about telecommuting: analyzing the characteristics of telecommuters in contrast to nontelecommuters, analyzing factors affecting the individual choice to telecommute, and incorporating telecommuting into traditional transportation forecasting models.     

New security measures for the international shipping community

On 1 July 2004 the new maritime security regulatory regime set out in the International Convention for the Safety of Life at Sea (SOLAS), 1974 as amended, namely the new chapter XI-2 on Special measures to enhance maritime security and the International Ship and Port Facility Security (ISPS) Code entered into force only 18 months after adoption by the SOLAS Conference in December 2002. Following the devastating terrorist acts of 11 September 2001 in the United States, the international community recognised the need to protect the international maritime transport sector against the threat of terrorism. IMO responded swiftly and firmly by developing these new requirements, which represent the culmination of co-operation between Governments, Government agencies, local administrations and shipping and port industries.     

Crystallographic structure of sea ice along a salinity gradient and environmental control of microalgae in the brine cells

Duplicate ice cores were taken in southeastern Hudson Bay (Canadian Arctic), at 8 stations along a transect, from the mouth of the Great Whale River to saline waters 25 km offshore. One core from each station was cut into 10-cm sections, which were melted at room temperature for determinations of salinity, nutrients, algal pigments and taxonomic composition of the microalgal assemblages. On the second core, thin sections were cut every 2 cm to optically determine the ratio of brine/gas pockets to the total sections. Relative volumes of brine in melted samples were computed from the observed ratios and calculated values, and used to convert per unit brine volume the concentrations of pigments, nutrients and algal cells, initially measured per unit volume of melted sample.Salinity of the melted samples indicate the presence of freshwater beneath the sea ice close to shore throughout the growth season, and the vertical salinity profiles suggest intermittent intrusions of freshwater. Nutrient concentrations in the brine were high, suggesting that microalgae in the brine cells were generally not nutrient limited. Concentrations of ice algae in the brine cells reached relatively high values, that are often of the same order as those reported for eutrophic marine waters. Statistical analyses identified the rate of ice growth as the most important factor controlling the vertical and horizontal distributions of algal biomass and taxonomic composition in the sea ice, along the salinity gradient. Higher biomasses were generally associated with slower ice growth and also possibly lower grazing activity. In addition, the rate of ice growth influenced the distribution of microalgal assemblages, with nitrogen limitation potentially playing a secondary role in some instances.     

The Chatter of Semi-Active On-Off Suspensions and its Cure

Semi-active suspensions are those in which otherwise passively generated damper forces are modulated using feedback control and small amounts of control effort. Recently it was discovered that two-stage, ON-OFF, semi-active control would chatter between the ON and OFF states in a manner similar to bang-bang, active control systems. This chatter is dependent upon the switching algorithm. This paper describes the dynamics of this chatter and suggests alternative control policies for its cure.     

Modelling route choice behaviour in multi-modal transport networks

The paper presents new findings on the influence of multi-modal trip attributes on the quality and competitiveness of inter-urban multi-modal train alternatives. The analysis covers the entire trip from origin to destination, including access and egress legs to and from the train network. The focus is on preferences for different feeder modes, railway station types and train service types as well as on the relative influence of time elements and transfer penalties. Data from dedicated surveys are used including individual objective choice sets of 235 multi-modal homebound trips in which train is the main transport mode. The observed trips have origins and destinations within the Rotterdam–Dordrecht region in The Netherlands with an average total trip time of 50 minutes. Hierarchical Nested Logit models are estimated to take account of unobserved similarities between alternatives at the home-end and the activity-end of the trip respectively, resulting in two-level nesting structures which differentiate between intercity (IC) and non-intercity railway station types at the upper level and between transit and private access modes at the lower level. In order to reflect the multi-dimensional structure of the data a more advanced so-called Multi-Nested GEV model according to the Principles of Differentiation has been estimated which significantly improves the explanatory power and stresses the importance of the home-end of the multi-modal trip.     

Contents Volume 32 2005

Contents Volume

Contents Volume 32 2005