Modelling service reliability of a heterogeneous train fleet operating on aged infrastructure

Abstract

ENGLISH ABSTRACT: The Passenger Rail Agency of South Africa is in the process of introducing new rolling stock into their current aged fleet of rolling stock. This poses several technical challenges relating to amongst other the operation of the mix of old and new trains on the same infrastructure. The objective of this study was therefore to determine the effect on service reliability in terms of punctuality, when old trains are incrementally replaced by new trains. Punctuality was measured by number of delays, total delay minutes and average delay duration over a specified time period. A discrete-event simulation model was developed using Anylogic simulation software. The line between Chris Hani and Cape Town stations on the Western Cape Metrorail network was chosen as case study for the model. Two cases were modelled with each consisting of 14 scenarios. Case 1 assumed no reliability improvement to the overall rail system. Since the specific route consisted of 14 trains shuttling to and from Cape Town, each scenario represented the replacement of an old train with a new train until the whole fleet consisted of only new trains. Case 2 modelled the same scenarios, except it was assumed that the system’s reliability was improved by an arbitrary value of 50%. In Case 1 a 29% improvement in number of delays, 37% improvement in total delay minutes, and 11% improvement in average delay duration were seen when Scenario 0 (base case) was compared to Scenario 14 (future case with all 14 old trains replaced). In Case 2 a 31% improvement in number of delays, 36% improvement in total delay minutes, and 7% improvement in average delay duration were seen. When Case 1 and 2 are compared on a scenario for scenario basis (e.g. Case 1, Scenario 0 compared to Case 2, Scenario 0) it was found that the 50% reliability improvement of the overall system resulted in an average improvement of 13% in number of delays, 19% in total delay minutes, and 6% in average delay duration. The overall improvement from zero new trains and no system reliability improvement (Case 1, Scenario 0) to 14 new trains and 50% system reliability improvement (Case 2, Scenario 14) resulted in a 39% reduction in number of delays, 47% reduction in total minutes delay, and 13% reduction in average delay duration. The model therefore shows how a train service can improve in terms of punctuality, when reliability improvements are made such as new rolling stock or overall system improvements that resolve primary delay causes. The findings of this study can therefore be used to support decisions related to capital investments into reliability improvements and new rolling stock commissioning strategies.

AFRIKAANSE OPSOMMING: Die Passasier Spoor-agentskap van Suid-Afrika is huidiglik in die proses om nuwe rollende materiaal in te faseer in die huidige vloot van rollende materiaal. Hierdie proses skep verskeie tegniese uitdagings ten opsigte van die bedryf van die mengsel van ou en nuwe treine op dieselfde infrastruktuur. Die doel van hierdie studie was om te bepaal wat die effek op diensbetroubaarheid in terme van stiptelikheid is, wanneer ou treine inkrementeel vervang word met nuwe treine. Stiptelikheid was gemeet deur hoeveelheid vertragings, totale vertragingsminute, en gemiddelde vertragingsduur oor `n gespesifiseerde tydperk. `n Diskrete-gebeurtenis simulasiemodel was ontwikkel met die gebruik van Anylogic sagteware. Die spoorlyn tussen Chris Hani- en Kaapstadstasie op die Wes-Kaapse Metrorail netwerk was gekies as gevallestudie vir die model. Twee gevalle was gemodeleer met elkeen wat bestaan uit 14 scenarios. Geval 1 het aangeneem dat geen betroubaarheidsverbeteringe aan die oorhoofse spoorwegsisteem aangebring was nie. Aangesien dié spesifieke roete 14 treine bevat wat na en van Kaapstad reis, stel elke scenario die inkrementele vervanging van ‘n ou trein met ‘n nuwe trein voor totdat die hele vloot uit slegs nuwe treine bestaan. Geval 2 het dieselfde scenarios gemodeleer, behalwe dat ‘n aaname gemaak was dat die betroubaarheid van die oorhoofse sisteem met 50% verbeter was. In Geval 1 was 29% verbetering in hoeveeldheid vertragings, 37% verbetering in totale vertragingsminute, en 11% verbetering in gemiddelde vertragingsduur gevind. In Geval 2 was 31% verbetering in hoeveeldheid vertraagings, 36% verbetering in totale vertragingsminute, en 7% verbetering in gemiddelde vertragingsduur gevind. Wanneer Geval 1 en 2 met mekaar vergelyk word op `n scenario-vir-scenario basis, was daar gevind dat die 50% betroubaarheidsverbetering aan die oorhoofse sisteem gelei het tot `n gemiddelde verbetering van 13% in hoeveelheid vertragings, 19% verbetering in totale vertragingsminute, en 6% verbetering in gemiddelde vertragingsduur. Die algemene verbetering vanaf geen nuwe treine en geen sisteem-betroubaarheidsverbetering tot 14 nuwe treine en 50% sisteemverbetering het gelei tot 39% verbetering in hoeveelheid vertragings, 47% verbetering in totale vertragingsminute, en 13% verbetering in gemiddelde vertragingsduur. Die model wys dus hoe `n treindiens kan verbeter in terme van stiptelikheid wanneer diensbetroubaarheid verbeteringe aangebring word soos nuwe rollende material en oorhoofse sisteems verbetering wat primêre vertraagings verminder. Die bevindings van die studie kan daarom gebruik word om besluitneemings te ondersteun met verband tot kapitale investeerings in diensbetroubaarheids verbeteringe en rollende material inbedryfsteling strategieë.