Access envelopes : a new accessibility mapping technique for transport and settlement planning

Abstract

The article describes the application of a GIS-based accessibility measurement technique suited to assessing the impact of both transport and spatial development strategies on the location-specific affordability of job access for poor households. The access envelope methodology extends existing accessibility measures by: explicitly accounting for public transport service patterns; including transport costs as a dimension of accessibility; and deriving a single intuitive measure of access reflecting the potential income earnable by a person living in a certain location, after paying for transport. Several case studies from the City of Tshwane are presented, illustrating its use for assessing spatial integration and transport initiatives. The cases demonstrate how Tshwane’s emerging Bus Rapid Transit (BRT) system selectively enhances accessibility to jobs, although its marginal accessibility benefit is reduced by the part-duplication of existing rail lines to core employment areas. While the BRT improves the net earning potential of low-income workers in certain areas, its ultimate benefits will significantly depend on its achievement of network effects – especially via the reduction of first/last-kilometer trip costs – and its ability to leverage higher density development within walking distance of the route. Accordingly, results obtained with the access-envelopes method carry significant implications for current transport planning in the main metro cities.

Die toepassing van ’n metode om die toeganklikheidsimpakte van beide vervoeren ruimtelike ontwikkelingstrategieë op die haalbaarheid van werksgeleenthede onder lae-inkomste huishoudings te beoordeel, word bespreek. Die metode is gegrond op Geografiese Inligtingstelsels (GIS), en verbeter bestaande metodes om toeganklikheid te meet deur openbare vervoerdienste direk in ag te neem; vervoeronkostes as a dimensie van toeganklikheid in ag te neem; en ’n enkele intuïtiewe indeks te ontwikkel om die potensiële inkomste van ’n person wat op ’n bepaalde plek woon, te bereken, inaggenome die koste en tyd wat aan vervoer bestee word. Gevallestudies van die Stad Tshwane word aangebied om die toepassing van die metode te illustreer. Die gevalle toon die mate waartoe Tshwane se opkomende Snelbusstelsel toeganklikheid tot bepaalde werksgebiede kan verbeter, ten spyte daarvan dat die inkrementele voordeel beperk word deur die feit dat die busstelsel bestaande treindienste gedeeltelik dupliseer, veral ten opsigte van bestaande kerngebiede in die stad. Die snelbus verbeter wel die netto potensiële inkomste van werkers, maar sy voordele sal uiteindelik afhang van die mate waartoe die kostes van die eerste/laaste kilometer van ritte verminder word, en die mate waarin verdigting en ontwikkeling in areas wat binne loopafstand van die roete is, behaal word.

Serapa sena se hlalosa tshebediso ya thekeniki ya ho fumana sohloe ha bobebe ka GIS, e sebedisetsoang ho sheba na transpoto le tswediso pele ya dibaka tse kholo di ama hakae mabapi le ho fhla mesebetsing ha bonolo le ho se utlloisi pokotho bohloko. Access envelope methodology e sarolla mekhoa ya ho fihla dibakeng tse hlokahalang ha bonoloka ho sebetsana le ditshebeletso tsa transpoto, haholo holo ditefello tsa transpotoya sechaba e le mokhoa oa ho bebofatsa ho fihla dibakeng tse hlokahalang le ho fana ka mokhoa o le mong oa ho fihla ha bobebo dibakeng tse hlokahalang o ipapisitseng le se motho a se kholang. Dipatlisiso tse ngata tse tsoang City of Tswane di bontsha tshebetso ya bona ya ho shebisisa kenyelletso ya dibaka le traspoto. Dipatlisiso di bontsha lka mokho Bus Rapid Transit (BRT) e thusitseng batho hore ba fihle mesebetsing ka nako teropong ya Tswane, le ha ho fihla ha bobebe ha eona ho ts’iroa ke diterene tse ne se ntse di le teng. Le ha BRT e ntlafatsa chelete ya batho basa kholeng haholo, ditla morao tsa eona tse hantle di ka thusoa ke ditefiso tse tlase le ho phahamiso trswelopele ya bona pela batho hore ba khona ho tsamaya ka maoto hofihla ho yona. Ha ho le joalo access envelopes method e bontsha ho eba le diphetoho tsa merero ya transpoto ka hara teropo tse kholo.