Francesc Soriguera

Requiem for Freeway Travel Time Estimation Methods Based on Blind Speed Interpolations Between Point Measurements

Travel time estimation from loop measurements has attracted extensive research in the last decade, resulting in numerous methodologies. Among these, those that rely on spot speed measurements at detector sites to obtain travel time estimation on the target stretch are the most intuitive. The key issue concerning these methods is the spatial generalization of point measurements over a freeway link. This paper shows that all speed interpolation methods that omit traffic dynamics and queue evolution do not contribute to better travel time estimations. All methods are inaccurate in congested and transition conditions, and the claimed relative benefits using various speed interpolation methods result from context-specific experiments. Therefore, these methods should be carefully used and not taken as perfect. Lacking a better approach, it is recommended to avoid overcomplicated mathematical interpolations and focus efforts on intelligent smoothing of the noisy loop detector data, reducing the fluctuations of short time interval aggregations while maintaining the immediacy of the measurements.

Assessment of Dynamic Speed Limit Management on Metropolitan Freeways

This article evaluates the impacts of dynamic speed limit strategies in metropolitan freeways. An objective function is defined in order to balance the benefits (e.g., reduction of congestion, pollutant emissions and fuel consumption, or increase in traffic safety) and costs (e.g., increase of free flow travel times). This function is generic in its nature, and could be used to assess any type of traffic management strategy. In particular, it is applied to the Barcelonas freeways dynamic speed limit management case study. The results suggest that the social profitability of dynamic speed limit (DSL) management in metropolitan freeways is limited. The main reason for this is the reduced effect of this kind of policy, if isolated in application, in alleviating congestion. It is emphasized that the absolute magnitude of the profitability is highly sensitive to the value given to each one of the social costs. The profitability of the policy would improve if the value of traffic externalities increased in relation to the marginal cost of travel times. A sensitivity analysis with respect to this last cost is presented. The potential synergies of applying DSL strategies jointly with other active traffic management policies should be considered as an issue for further research.

Travel Time Measurement Using Toll Infrastructure

Travel time and its reliability are key factors in traffic management systems. They are the best indicators of the level of service in a road link and perhaps the most important variables for measuring congestion. A new approach is presented: it estimates highway travel time with the use of the existing toll highway infrastructure. A simple, efficient algorithm was developed to estimate the single-section travel time (i.e., time required to travel between two consecutive ramps on the highway) and the exit time for each ramp (i.e., time required to travel along the exit link plus the time required to pay the fee at the toll gate). With a combination of these two estimations, all required route travel times can be calculated. The proposed algorithm overcomes some limitations of other methods, such as information delay in long routes and excess travel time estimation due to accumulated exit times. The method was applied to the AP-7 highway near Barcelona, Spain, and the results obtained were reasonable and accurate.

Optimization of Handling Equipment in the Container Terminal of the Port of Barcelona, Spain

Most studies concerning port operations focus on the operation between ship and wharf. However, other port activities may also lead to congestion. In general, the capacity of the handling equipment used to transfer the container between the wharf and the storage yard is critical. This paper analyzes the internal transport subsystem in a marine container terminal and investigates the effect of the type of handling equipment used. The aim is to analyze the behavior of the handling equipment and to model its optimization. Determining a better equipment type to use is not the main concern of this paper. Queuing theory is applied, and simulation is conducted to analyze the system. To perform the analyses, measurements of parameters related to the terminal are required. These parameters were obtained from the container terminal at Barcelona, Spain, one of the best-positioned logistic platforms on the Mediterranean Sea. The results indicate that assignment of the handling equipment resources to an individual wharf crane in a particular berth is not advisable, since any decentralized decision system involves more resources. The handling equipment resources must be assigned to the berth as a whole to obtain greater efficiency, but then a focus on operation planning and reliability is required. The availability of two or three wharf cranes in a berth is not crucial in terms of efficiency; however, it could increase productivity in the berth significantly.

Optimization of Internal Transport Cycle in a Marine Container Terminal Managed by Straddle Carriers

Combined with the success of containerization, globalization has brought about tremendous increases in container transport around the world. Increased container transport leads to larger container ships, which increase demands on seaport container terminals and their equipment. In this situation, the success of container terminals depends on a fast transshipment process combined with reduced costs. It is thus necessary to optimize the three main logistic processes at seaport container terminals: loading and unloading container ships, storing containers, and receiving and delivering containers to and from the hinterland. In another process, the internal transport subsystem ensures the interconnection between previous logistic activities. The optimization of an internal transport cycle is presented for a marine container terminal managed by straddle carriers (SCs), which are among the most used technologies for container transfer. Three subsystems are analyzed in detail: landside transportation, container storage in the yard, and quayside transportation. The conflicts and decisions that arise from operations in these subsystems are analyzed, and optimization algorithms are proposed. Moreover, a simulation is run on Spains Barcelona Container Terminal to test the algorithms and compare different SC operation strategies (e.g., single cycle versus double cycle) and different-sized fleets of handling equipment. The simulation model is explained in detail, and the main decision-making algorithms from the model are presented and formulated.

Freeway Travel-Time Information: Design and Real-Time Performance Using Spot-Speed Methods

This paper shows that the precision of a freeway travel-time information system, in a real-time context, is not related solely to the accuracy of the measurement. Immediacy in reporting the information and forecasting capabilities play a role. Therefore, focusing only on the accuracy of the travel-time measurement is a myopic approach, which can lead to counterintuitive results. Specifically, it is claimed that, using travel times estimated with the traditional spot-speed midpoint algorithm, the performance of the real-time information system when evolving traffic conditions prevail is better than using much more accurate directly measured travel times (MTTs). Guidelines for an adequate configuration of the common parameters of the system are provided. In addition, real-time context enhancements for travel-time estimation methods based on punctual speed measurements are proposed. These are addressed by taking into account an easy and practical implementation. They have been proven to work well in an empirical application on a Spanish freeway.

Effects of dynamic speed limits on a Dutch freeway

This paper describes the effects of dynamic speed limit (DSL) control on a three-lane section on the A13 Freeway in Rotterdam, Netherlands. The main objective was to contrast the latest empirical findings from an experiment conducted in Barcelona, Spain, in which the main line metering capability (i.e., gating, or main line flow restriction) was questioned because of subcritical speed limits (e.g., speed limits down to 40 km/h). Moreover, according to the results of the study conducted in Barcelona, the validity of the current fundamental diagram models accounting for DSL control could be strongly compromised. This investigation took advantage of the huge amount of empirical traffic data recorded by the Dutch government and of the DSL control strategies present on most freeways in the Netherlands. The data were treated to identify stationary periods of traffic. To this end, a method that was found to be reproducible elsewhere and computerized into an algorithm was developed. The fundamental diagram was used as a graphical tool to assess the results. The main findings do not contradict the observations from the study performed in Barcelona. Flows of 1,850 vehicles per hour per lane were steadily observed at the subcritical speed limit of 50 km/h. The reactive nature of DSL control implemented in the Netherlands implies that very low speed limits do not affect a wide range of traffic states. This finding hampered the possibility to extend this conclusion. Further research with fewer limiting DSL control strategies is necessary to clarify the extent of the phenomenon considered.