Measuring accessibility and congestion in Accra

Abstract

Based on extensive GPS measurements, the article addresses the level of intra-urban accessibility in Accra, Ghana, and provides indications of the level of congestion. Traffic flows within the urban area are analysed with respect to speed, time-of-day, direction, road type, and land cover type. The speed information is extrapolated to cover the total mapped urban road network with time- and direction-specific data. A series of time-distance maps are created using network analysis to illustrate the level of accessibility at different times of the day and from different directions relative to the city centre. The article discusses the methodological potential of and barriers to applying GPS tracklog points for analysing traffic flows within an urban road network. Solutions are suggested for filtering GPS measurements, matching GPS measurements with the relevant transport links, even at intersections, and for providing direction- and time-specific flow analysis.

Keywords:

• accessibility
• Accra
• congestion
• GPS
• urban fringe

Notes

1. M.N.A. Akofio-Sowah ‘Modeling traffic congestion in the Accra metropolitan area’, Honours project, Smith College, Northampton, MA, 2010.

2. A.S. Jensen, P. Bro & H. Harder ‘Identification and cleansing of scatter in GPS-surveys in urban environments’. Technical report, Department of Architecture and Design, Aalborg University, 2009.