The objective of this paper is to give an overview of various reliability concepts that have been developed in the last decades. The paper first summarises various…
The objective of this paper is to give an overview of various reliability concepts that have been developed in the last decades. The paper first summarises various indicators that have been developed in order to measure the reliability of a network and then looks at techniques to calculate these indicators. The usefulness and limitations of the different indicators is discussed. The paper suggests that there is no single perfect indicator but that the choice of indicator and technique depends on several factors, including the viewpoint of the analyst and the type and range of interventions being considered. In order to assess the impact of incidents the authors propose to distinguish between three types of intervention, namely “benevolent”, “neutral” or random, and “malevolent”. Also discussed is why the provision of up-to-date information to the traveller has a central role to play when trying to minimise the impact of an incident.
Risk evaluation and management methods are used to assess the reliability of a New Zealand inter-urban road network, which is subject to closures due to snow and ice, earthquakes, volcanic activity and road accidents. Using the probabilities and consequences of closures of various durations, the expected annual costs of closures are determined for each hazard. The benefit-cost ratios for various risk mitigation options are also identified. The importance of considering both the probabilities and consequences of closures is discussed.
It is found that a ‘high-frequency, low-consequence’ hazard (snow and ice) has the highest expected annual cost, and higher than for the ‘low-frequency, high-consequence’ hazards (earthquakes and volcanic activity). It is also found that not allowing for elasticity in the demand for travel (e.g. trips being cancelled or postponed because of road closures) leads to inaccurate estimates of the costs of closure.
It is concluded that it is important to allow for the behavioural responses of network users when estimating the costs of closures, and that more attention should be given to ‘high-frequency, low-consequence’ hazards, in order to maximise the economic benefits of expenditure on risk mitigation.
Computer models are often used for studying the effects of changing conditions in the road network. State-of-the-art macroscopic models generally take some kind of network…
Computer models are often used for studying the effects of changing conditions in the road network. State-of-the-art macroscopic models generally take some kind of network equilibrium approach and therefore have difficulties in appropriately representing short-term capacity reductions, probably resulting in too low estimates of delays. Recently developed dynamic models may be more promising. The purpose of this paper is to investigate the implications of model choice further, as well as the possibilities to study effects of short-term incidents. Three different computer programs were used: TRACKS, SATURN, and Paramics. The results show that microsimulation is a feasible tool for studying short-term disturbances in the road transportation system.
This study aims to identify the determinants of transport mode choice and the constraints on shifting freight in New Zealand (NZ) from road to rail and/or coastal…
This study aims to identify the determinants of transport mode choice and the constraints on shifting freight in New Zealand (NZ) from road to rail and/or coastal shipping, and to quantify the trade-off between factors affecting shippers’ perceptions, to assist in increasing the share of freight moved by non-road transport modes.
A revealed preference survey of 183 freight shippers, including small and medium enterprises and freight agents in NZ, is used to investigate whether freight shippers’ characteristics affect their ranked preference for attributes related to mode choice and modal shift. Additionally, a rank-ordered logistic (ROL) model is estimated using the ranking data.
The results reveal several distinct types of transport mode choice behaviour within the sample and show how the preferences for timeliness, cost, accessibility, damage and loss, customer service, and suitability vary between industry groups and business types. Also, the ROL method allows us to identify heterogeneity in preferences for mode choice and mode shift factors for freight within NZ.
The results imply that NZ shippers ranked transport time as the most significant constraint upon distributing goods by rail, while accessibility and load size were the most significant constraints upon using coastal shipping. The study also identifies how NZ shippers’ modal shift constraints vary according to the firm’s individual or logistical characteristics.
This study informs freight transport policy makers about the needs of NZ shippers by providing quantitative measures of the intensity of preference for the various mode choice factors.
Those involved in freight transport have a better basis for formulating transport policy.