Applying Operations Research techniques to planning of train shunting

In this paper, we discuss a model-based algorithmic approach for supporting planners in the creation of shunt plans for passenger trains. The approach provides an example of a mathematical model and a corresponding solution approach for model based support. We introduce a four-step solution approach and we discuss how the planners are supported by this approach. Finally, we present computational results for these steps and give some suggestions for further research.A* search;railway optimization;real world application;routing

The new Dutch timetable: The OR revolution

In December 2006, Netherlands Railways introduced a completely new timetable. Its objective was to facilitate the growth of passenger and freight transport on a highly utilized railway network, and improve the robustness of the timetable resulting in less train delays in the operation. Further adjusting the existing timetable constructed in 1970 was not option anymore, because further growth would then require significant investments in the rail infrastructure. Constructing a railway timetable from scratch for about 5,500 daily trains was a complex problem. To support this process, we generated several timetables using sophisticated operations research techniques, and finally selected and implemented one of these timetables. Furthermore, because rolling-stock and crew costs are principal components of the cost of a passenger railway operator, we used innovative operations research tools to devise efficient schedules for these two resources. The new resource schedules and the increased number of passengers resulted in an additional annual profit of 40 million euros ($60 million) of which about 10 million euros were created by additional revenues. We expect this to increase to 70 million euros ($105 million) annually in the coming years. However, the benefits of the new timetable for the Dutch society as a whole are much greater: more trains are transporting more passengers on the same railway infrastructure, and these trains are arriving and departing on schedule more than they ever have in the past. In addition, the rail transport system will be able to handle future transportation demand growth and thus allow cities to remain accessible. Therefore, people can switch from car transport to rail transport, which will reduce the emission of greenhouse gases.

Applying Operations Research techniques to planning of train shunting

In this paper, we discuss a model-based algorithmic approach for supporting planners in the creation of shunt plans for passenger trains. The approach provides an example of a mathematical model and a corresponding solution approach for model based support. We introduce a four-step solution approach and we discuss how the planners are supported by this approach. Finally, we present computational results for these steps and give some suggestions for further research

Rescheduling in passenger railways: the rolling stock rebalancing problem

This paper addresses the Rolling Stock Rebalancing Problem (RSRP) which arises within a passenger railway operator when the rolling stock has to be rescheduled due to changing circumstances. RSRP is relevant both in the short-term planning stage and in the real-time operations. RSRP has as input a timetable and a rolling stock circulation where the allocation of the rolling stock among the stations at the start or at the end of a certain planning period does not match with the allocation before or after that planning period. The problem is then to modify the input rolling stock circulation in such a way that the number of remaining off-balances is minimal. If all off-balances have been solved, then the obtained rolling stock circulation can be implemented in practice. For practical usage of solution approaches for RSRP, it is important to solve the problem quickly. Since we prove that RSRP is NP-hard, we focus on heuristic solution approaches: we describe two heuristics and compare them with each other on (variants of) real-life instances of NS, the main Dutch passenger railway operator. Finally, to get further insight in the quality of the proposed heuristics, we also compare their outcomes with optimal solutions obtained by solving an existing rolling stock circulation model

Remodeling of Abdominal Aortic Angulation and Curvature After Endovascular Aneurysm Repair in Patients With vs Without Late Type Ia Endoleak or Endograft Migration

Purpose: To investigate aortic remodeling of the supra- and infrarenal aorta from preoperative to 1 month and midterm follow-up after endovascular aneurysm repair (EVAR) by analyzing changes in angulation and curvature in patients with vs without late type Ia endoleak or device migration. Materials and Methods: From a multicenter database, 35 patients (mean age 76 +/- 5 years; 31 men) were identified with late (>1 year) type Ia endoleak or endograft migration (>= 10 mm) and defined as the complication group. The control group consisted of 53 patients (mean age 75 +/- 7 years; 48 men) with >1-year computed tomography angiography (CTA) follow-up and no evidence of endoleaks. Suprarenal and infrarenal angles were measured on centerline reconstructions of the preoperative, 1-month, and midterm CTA scans. The value and location relative to baseline of maximum suprarenal and infrarenal curvature were determined semiautomatically using dedicated software. Changes were determined at 1 month compared with the preoperative CTA and at midterm compared with 1 month. Results: Preoperative suprarenal angulation was significantly greater in the complication group compared to the controls (34 degrees +/- 18 degrees vs 24 degrees +/- 17 degrees, p=0.008). It decreased significantly at 1 month in the complication group (29 degrees +/- 16 degrees, p=0.011) and at midterm follow-up in the controls (20 degrees +/- 19 degrees, p Conclusion: At midterm follow-up, significant differences in supra- and infrarenal angulation and curvature were observed between patients with vs without type Ia endoleak or migration. The location of the maximum curvature shifted distally in patients with complications. The aortic morphology is more stable during midterm follow-up in the patients without endoleaks

Aneurysm Sac Dynamics and its Prognostic Significance Following Fenestrated and Branched Endovascular Aortic Aneurysm Repair

Objective: This study aimed to assess aneurysm sac dynamics and its prognostic significance following fenestrated and branched endovascular aneurysm repair (F/BEVAR). Methods: Patients undergoing F/BEVAR for degenerative complex aortic aneurysm from 2008 to 2020 at two large vascular centres with two imaging examinations (30 day and one year) were included. Patients were categorised as regression and non-regression, determined by the proportional volume change (&gt; 5%) at one year compared with 30 days. All cause mortality and freedom from graft related events were assessed using Kaplan–Meier methods. Factors associated with non-regression at one year and aneurysm sac volume over time were examined for FEVAR and BEVAR independently using multivariable logistic regression and linear mixed effects modelling. Results: One hundred and sixty-five patients were included: 122 FEVAR, of whom 34% did not regress at one year imaging (20% stable, 14% expansion); and 43 BEVAR, of whom 53% failed to regress (26% stable, 28% expansion). Following F/BEVAR, after risk adjusted analysis, non-regression was associated with higher risk of all cause mortality within five years (hazard ratio [HR] 2.56, 95% confidence interval [CI] 1.09 – 5.37; p = .032) and higher risk of graft related events within five years (HR 2.44, 95% CI 1.10 – 5.26; p = .029). Following multivariable logistic regression, previous aortic repair (odds ratio [OR] 2.56, 95% CI 1.11 – 5.96; p = .029) and larger baseline aneurysm diameter (OR/mm 1.04, 95% CI 1.00 – 1.09; p = .037) were associated with non-regression at one year, whereas smoking history was inversely associated with non-regression (OR 0.21, 95% CI 0.04 – 0.96; p = .045). Overall following FEVAR, aneurysm sac volume decreased significantly up to two years (baseline vs. two year, 267 [95% CI 250 – 285] cm 3 vs. 223 [95% CI 197 – 248] cm 3), remaining unchanged thereafter. Overall following BEVAR, aneurysm sac volume remained stable over time. Conclusion: Like infrarenal EVAR, non-regression at one year imaging is associated with higher five year all cause mortality and graft related events risks after F/BEVAR. Following FEVAR for juxtarenal aortic aneurysm, aneurysm sacs generally displayed regression (66% at one year), whereas after BEVAR for thoraco-abdominal aortic aneurysm, aneurysm sacs displayed a concerning proportion of growth at one year (28%), potentially suggesting a persistent risk of rupture and consequently requiring intensified surveillance following BEVAR. Future studies will have to elucidate how to improve sac regression following complex EVAR, and whether the high expansion risk after BEVAR is due to advanced disease extent.</p

Vascular clamping in liver surgery: physiology, indications and techniques

This article reviews the historical evolution of hepatic vascular clamping and their indications. The anatomic basis for partial and complete vascular clamping will be discussed, as will the rationales of continuous and intermittent vascular clamping

Covered stents versus Bare-metal stents in chronic atherosclerotic Gastrointestinal Ischemia (CoBaGI): Study protocol for a randomized controlled trial

Background: Chronic mesenteric ischemia (CMI) is the result of insufficient blood supply to the gastrointestinal tract and is caused by atherosclerotic stenosis of one or more mesenteric arteries in > 90% of cases. Revascularization therapy is indicated in patients with a diagnosis of atherosclerotic CMI to relieve symptoms and to prevent acute-on-chronic mesenteric ischemia, which is associated with high morbidity and mortality. Endovascular therapy has rapidly evolved and has replaced surgery as the first choice of treatment in CMI. Bare-metal stents (BMS) are standard care currently, although retrospective studies suggested significantly highe

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

The New Dutch Timetable: The O.R. Revolution

(Winner of the Franz Edelman Award - Achievement in Operations Research, 2008) In December 2006, Netherlands Railways introduced a completely new timetable. Its objective was to facilitate the growth of passenger and freight transport on a highly utilized railway network and improve the robustness of the timetable, thus resulting in fewer operational train delays. Modifications to the existing timetable, which was constructed in 1970, were not an option; additional growth would require significant investments in the rail infrastructure. Constructing a railway timetable from scratch for about 5,500 daily trains was a complex problem. To support this process, we generated several timetables using sophisticated operations research techniques. Furthermore, because rolling-stock and crew costs are principal components of the costs of a passenger railway operator, we used innovative operations research tools to devise efficient schedules for these two resources. The new resource schedules and the increased number of passengers resulted in an additional annual profit of E40 million ($60 million); the additional revenues generated approximately E10 million of this profit. We expect this profit to increase to E70 million ($105 million) annually in the coming years. However, the benefits of the new timetable for the Dutch society as a whole are much greater: more trains are transporting more passengers on the same railway infrastructure, and these trains are arriving and departing on schedule more than they ever have in the past. In addition, the rail transport system will be able to handle future transportation demand growth and thus allow cities to remain accessible to more people. Therefore, we expect that many will switch from car transport to rail transport, thus reducing the emission of greenhouse gases