Optimal toll locations and toll levels in congestion pricing schemes: a case study of Stockholm

As congestion pricing has moved from theoretical ideas in the literature to real-world implementation, the need for decision support when designing pricing schemes has become evident. This paper deals with the problem of finding optimal toll levels and locations in a road traffic network and presents a case study of Stockholm. The optimisation problem of finding optimal toll levels, given a predetermined cordon, and the problem of finding both optimal toll locations and levels are presented, and previously developed heuristics are used for solving these problems. For the Stockholm case study, the possible welfare gains of optimising toll levels in the current cordon and optimising both toll locations and their corresponding toll levels are evaluated. It is shown that by tuning the toll levels in the current congestion pricing cordon used in Stockholm, the welfare gain can be increased significantly, and furthermore improved by allowing a toll on a major bypass highway. It is also shown that, by optimising both toll locations and levels, a congestion pricing scheme with welfare gain close to what can be achieved by marginal social cost pricing can be designed with tolls being located on only a quarter of the tollable links.     

Ship sense—striving for harmony in ship manoeuvring

Ship manoeuvring is something that many seafarers perform, although little attention has been devoted to this in research literature. The topic has generally been explained by members of the trade as gaining knowledge through experience. The purpose of this study was to identify which factors contribute to the perceived state of a ship’s physical condition during manoeuvring. Eight master mariners were interviewed. The data resulted in a division of a sea voyage into three different phases, each requiring varying levels of effort from the bridge crew. The results further describe how the shiphandler strives for harmony between his ship and the environment. This is accomplished by personal factors such as spatial awareness, knowledge and experience to handle environmental factors of context, situation and vessel specific factors of inertia and the use of navigational instruments.     

Evacuation in practice — Observations from five full scale exercises

Evacuating a ship is a difficult task which normally is performed under severe and demanding conditions, exposing both crew members and passengers on board to an extreme and demanding situation. To be prepared for an incident happening on board and shouldering this responsibility is part of the everyday reality of the crew members’ work situation. This study reports the results from observations made on board five passenger ships performing full scale exercises with participants acting as passengers. The results pointed out four problem areas; the safety organization, the ability to perform tasks, the handling of life vests and communication. These areas represented an uncertainty in the requirements associated with the crew members’ role in the safety organization implied. There was also evidence of difficulties in the crews’ performing of different tasks, problems with donning life vests and insufficient communication. The crew member groups on board differ in their skills and knowledge to handle an evacuation situation. These groups need to be studied separately and systematically in order to determine how they comprehend their work situation and what their needs of preparation and training are in order to feel content with meeting the demands of their role in the safety organization.     

Surrogate‐based optimization of cordon toll levels in congested traffic networks

The benefit, in terms of social surplus, from introducing congestion charging schemes in urban networks is depending on the design of the charging scheme. The literature on optimal design of congestion pricing schemes is to a large extent based on static traffic assignment, which is known for its deficiency in correctly predict travel times in networks with severe congestion. Dynamic traffic assignment can better predict travel times in a road network, but are more computational expensive. Thus, previously developed methods for the static case cannot be applied straightforward. Surrogate‐based optimization is commonly used for optimization problems with expensive‐to‐evaluate objective functions. In this paper, we evaluate the performance of a surrogate‐based optimization method, when the number of pricing schemes, which we can afford to evaluate (because of the computational time), are limited to between 20 and 40. A static traffic assignment model of Stockholm is used for evaluating a large number of different configurations of the surrogate‐based optimization method. Final evaluation is performed with the dynamic traffic assignment tool VisumDUE, coupled with the demand model Regent, for a Stockholm network including 1240 demand zones and 17 000 links. Our results show that the surrogate‐based optimization method can indeed be used for designing a congestion charging scheme, which return a high social surplus. Copyright © 2016 John Wiley & Sons, Ltd.