16 research outputs found
Chemical Modifications of Hyaluronan using DMTMM-Activated Amidation
No full textAn alternative approach to chemically modifying hyaluronan (HA) has been investigated. The triazine derivative 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium (DMTMM) has been used to activate carboxylic groups on HA, which react further to form stable amide bonds with primary and secondary amines. The reaction can either be used to couple monoamines to HA or to produce hydrogels by using diamines that form crosslinks between the HA chains. The reaction between HA and DMTMM has been investigated and optimized in regard to degree of substitution (DS). Analysis using SEC-LC-UV demonstrated that the reaction was successful in coupling benzylamine to HA with a DS of 40%. Gel formation was successful using hexamethylene diamine as a crosslinker. Results also show that the reaction can be controlled by either the DMTMM or the amine concentration so that a specific degree of substitution or crosslinking is achieved. The stability of DMTMM has also been examined, and degradation studies of DMTMM in H2O at 50 °C with 1H NMR analysis show that 11% of the starting material remains after 48 hours. The reaction has proven to be an effective alternative to other modification methods with cheap reagents, simple procedures and the ability to control the amount of modification. Further investigations are nonetheless required in order to determine the full potential the DMTMM-activated amidation of HA
A heuristic method for finding congestion pricing schemes in traffic networks with modal choice
No full textIn this paper we extend a previously developed heuristic procedure, with a modal choice model, to solve the congestion pricing problem of simultaneously finding the optimal number of toll facilities, their corresponding location and toll levels. When considering a congestion pricing scheme the cost of collecting the tolls can not be disregarded. The objective is wherefore to maximize the net social surplus, which is the social surplus minus the cost of collecting the tolls. The heuristic method is an iterative solution procedure, in which the integer part of the objective function is approximated by a continuous function. A version of the Sioux Falls network (76 links) is used to demonstrate the solution procedure. The solution is a congestion pricing scheme which divide the network into four zones, by locating tolls on 27 links. This solution yields a social surplus which is only 13.5% lower than the marginal social cost pricing solution.</p
Estimation of Volume Delay Functions for Urban Environments Based on an Analytical Intersection Model
No full textThis paper describes a method for estimating parameters in volume delay functions. The volume delay function is a central part of static traffic assignment models and describes how the travel time on road link changes with traffic demand. The proposed estimation method is based on that the volume delay function is divided into two parts, one part describing the link travel time and delay and one part describing the intersection delay. The parameters for the link and intersection parts are estimated separately. Collecting data for the link part is seldom a problem. However, earlier experiences have shown that it is both difficult and expensive to collect data on intersection delay. We have used an approach in which the intersection delay data is taken from a model for calculating intersection delay, in this case the analytical intersection model CAPCAL. The developed estimation method has been exemplified on one road type and road environment. A sensitivity analysis has been conducted in order to investigate how large influence that the different assumptions on the road factors have on the volume delay function. The conclusions are that the flow levels on the cross road, the intersection density, the share of straight forward traffic, and the share of different intersection types has the largest influence, and thus should be prioritized when collecting road type data.</p
Towards optimal locations and toll levels in congestion pricing schemes
No full textThis paper addresses the problem of designing a road congestion pricing scheme with link tolls. The problem involves decisions on where to locate the toll collecting facilities and what tolls to charge the road users. We formulate this problem as a bi-level program, with the objective to maximize the net social surplus, which include the cost of setting up and operate the toll collection system. A previously developed heuristic method is applied to find close to optimal toll locations and charges for a traffic network representing the Stockholm region. The result is compared with the current congestion pricing scheme in Stockholm.</p
A heuristic method for finding congestion pricing schemes in transportation networks with modal choice
No full textHeuristic algorithms for a second-best congestion pricing problem
No full textDesigning a congestion pricing scheme involves a number of complex decisions. Focusing on the quantitative parts of a congestion pricing system with link tolls, the problem involves finding the number of toll links, the link toll locations and their corresponding toll level and schedule. In this paper, we develop and evaluate methods for finding the most efficient design for a congestion pricing scheme in a road network model with elastic demand. The design efficiency is measured by the net social surplus, which is computed as the difference between the social surplus and the collection costs (i.e. setup and operational costs) of the congestion pricing system. The problem of finding such a scheme is stated as a combinatorial bi-level optimization problem. At the upper level, we maximize the net social surplus and at the lower level we solve a user equilibrium problem with elastic demand, given the toll locations and toll levels, to simulate the user response. We modify a known heuristic procedure for finding the optimal locations and toll levels given a fixed number of tolls to locate, to find the optimal number of toll facilities as well. A new heuristic procedure, based on repeated solutions of a continuous approximation of the combinatorial problem is also presented. Numerical results for two small test networks are presented. Both methods perform satisfactorily on the two networks. Comparing the two methods, we find that the continuous approximation procedure is the one which shows the best results.</p
Travel demand estimation and network assignment based on cellular network data
No full textCellular networks signaling data provide means for analyzing the efficiency of an underlying transportation system and assisting the formulation of models to predict its future use. This paper describes how signaling data can be processed and used in order to act as means for generating input for traditional transportation analysis models. Specifically, we propose a tailored set of mobility metrics and a computational pipeline including trip extraction, travel demand estimation as well as route and link travel flow estimation based on Call Detail Records (CDR) from mobile phones. The results are based on the analysis of data from the Data for development "D4D" challenge and include data from Cote dlvoire and Senegal. (C) 2016 Elsevier B.V. All rights reserved.Funding Agencies|Swedish Governmental Agency for Innovation Systems (VINNOVA)</p
Applications of Simplicial Decomposition with Nonlinear Column Generation to Nonlinear Network Flows
No full text. The simplicial decomposition method for linearly constrained nonlinear programs has been proven to be efficient for certain classes of structured large-scale problems. This method alternates between a multi-dimensional search over a restriction of the feasible set and an augmentation of the restriction through the solution of a linear column generation problem. The quality of the columns generated may however be very poor, since the first-order approximation of the objective function is used globally. As a means for improving the quality of the columns in a simplicial decomposition method, we consider using nonlinear (e.g., second-order) approximations of the objective function in the augmentation phase. This modification leads to the generation of non-extreme point columns. The new method is applied to two nonlinear network flow models: the traffic assignment problem and the stochastic transportation problem. Numerical experiments indicate that significant time and storage savings c..
Evaluation of travel time estimation based on LWR-v and CTM-v: A case study in Stockholm
No full textReal-time estimations of current and future traffic states are an essential part of traffic management and traffic information systems. Within the Mobile Millennium project considerable effort has been invested in the research and development of a real-time estimation system that can fuse several sources of data collected in California. During the past year this system has been adapted to also handle traffic data collected in Stockholm. This paper provides an overview of the model used for highways and presents results from an initial evaluation of the system. As part of the evaluation process, GPS data collected in an earlier field-test and estimations generated by the existing system used by the TMC in Stockholm, are compared with the estimations generated by the Mobile Millennium system. Given that the Mobile Millennium Stockholm system has not undergone any calibration, the results from the evaluation are considered promising. The estimated travel times correspond well to those measured in the field test. Furthermore, the estimations generated by the Mobile Millennium system can be regarded as superior to those of existing traffic management system in Stockholm. The highway model was found to perform well even with a reduction in the number of sensors providing data. The findings of this study indicate the robustness of the Mobile Millennium system and demonstrate how the system can be migrated to other geographical areas with similar sources of available data.</p
Appraisal of cycling infrastructure investments using a transport model with focus on cycling
No full textCost-benefit analysis (CBA) for cycling infrastructure investments are less sophistically developed compared to the ones for private cars and public transport, and one of main reasons is the lack of “well-developed” transport models for cycling. In this study, a dedicated transport model for cycling is used to appraise cycling infrastructure investments in Stockholm, Sweden. The model captures the impact of a change in cycling infrastructure on cycling route choice, mode choice, destination choice and trip generation and calculates cycling flow on link level. the generalised cost measure defined in the route choice model captures the impact of cycling infrastructure. Results suggest that although cycling flow on the links with investment may increase substantially, only a small share comes from modal shift and thus the external effects such as reducing car congestion and emissions are marginal. For all three scenarios investigated, over 97% of the benefits measured in the unit of generalised cost belong to the existing cyclists. The route choice model does not minimize travel time but generalised cost which also measures health, safety benefits and other possible benefits that may be considered by the cyclists when they choose to cycle. In fact, travel time saving benefits of the investments evaluated in this paper are all negative. The existing effect evaluation models therefore need to be adjusted to be more consistent with the transport model.</p
