Rapid spatial growth and population growth in Dar es Salaam, coupled with a rise in car ownership, is putting strain on Dar es Salaam’s insufficient road network. City residents have to grapple with heavy traffic delays and the inner city areas are practically inaccessible during rush hours.
Collecting network data from the users of OpenStreetMap, a free and open-access online map service, a team of researchers employed twenty-first century technology to investigate Dar es Salaam’s twentieth century road network. Aside from painting a fascinating picture of how long it takes citizens to get from one point in the city to another the results of the study, published in Habitat International, highlight that Dar es Salaam’s infrastructure has become sorely inadequate for its transportation needs.
Urbanafrica.net spoke to Lasse Møller-Jensen, head of the Section for Geography at the University of Copenhagen, about his research and about what the findings mean for Dar es Salaam’s next steps, and for transportation networks around the continent.
Maitagorri Schade: What is accessibility, and what is its significance for the city?
Lasse Møller-Jensen: [Accessibility] concerns the ability of people or goods to reach their different destination points within the city, which can be work places, markets, social visits. If the accessibility is low, it means that people cannot easily get to work and that goods cannot be distributed. You get an inefficient city with many hours lost in traffic and a low capacity for moving around.
MS: Why did you pick Dar es Salaam as the location for your study?
LMJ: We have done a similar study for Accra, Ghana, and wanted to see whether similar conditions apply for Dar (which they do to a large extent). We have been running a project for four years (funded by Danida with IDS, University of Dar es Salaam as lead partner) on general problems related to urban growth in Tanzania. The transport issue is very obvious to people working in Dar.
MS: What is the one main problem for accessibility in Dar es Salaam, based on your research? What are the effects of this problem on city residents?
LMJ: The rapid spatial growth and population growth and growth in car ownership is accommodated by an insufficient road network that has only been slightly expanded for many years. The effect is heavy congestion forcing people to leave by four in the morning to get to work.
MS: How would you describe the mutual relation of urban growth and accessibility over time in Dar es Salaam?
LMJ: Dar’s population growth has resulted in very extensive spatial growth – mostly of an informal nature. The existing radial roads are not well connected to the vast new urban areas on the fringe of the city. The connecting roads are often rough and slow, developing in a haphazard manner. With further expansion this problem gets worse.
With an expanding population the pressure on the central areas also increases, making them almost inaccessible during rush hours. Further high-rise development which is taking place here, will also make this problem worse.
MS: How did you define/measure congestion, and why are time delays the key feature you focused on for this accessibility study?
LMJ: Our definition is one of several from the literature: the difference between actual speed levels at certain times of the day and the potential speed if you were the only car on the road (free flow) provides an indication of the level of congestion. We have used speed data reported by other studies. This paper will be followed by a study based on GPS speed data that we have obtained recently which will also look into the speed levels when using minibuses and access to the new urban areas.
MS: What would you recommend as the primary means of improving these time delays?
LMJ: Overall: planning and implementing infrastructure ahead of development, which is difficult in this context for various reasons including the pace of the development. Introduction of efficient rail-based public transport to supplement. To specifically access car transport: more high capacity outer ring roads would help (as well as the bridge which is being built).
MS: You used average speed data to understand mobility patterns in Dar es Salaam. Are there issues with this approach? For example, how many road users would have an experience similar to this average?
LMJ: This paper is based on speed data reported by other studies which we have extended to similar roads in the total road network in order to be able to do the analysis. […] These studies describe their speed data as related to traveling by car between specific measuring points. (The speed values must be seen as approximations when applied to the rest of the network).
There could be issues concerning how well the analysis reflects the travel mode of all inhabitants of Dar, since the applied speed data refers to regular cars. It is clearly of high interest to look at other means of transportation and conditions for different groups also. We have recently collected GPS track log data in Dar using both cars, minibuses, three- and two-wheel ‘motorcycles’ etc. for a forthcoming paper with a focus on the accessibility to specific new urban fringe areas. However, the car speed data from rush hour and ‘free flow’ conditions that we have used for this study does provide a good indication of the influence of road congestion on accessibility.
MS: Do you think reducing road delays is the key to improving accessibility in Dar es Salaam?
LMJ: It is one important aspect . But more efficient public transport in separate rails or lanes is another.
MS: You mention the implementation of new transit systems, such as the BRT (Bus Rapid Transit system) which is currently being built. What is your prediction for how the BRT system might affect accessibility and congestion?
LMJ: I don’t know, but the potential is there if it can run as intended and if people will be able to use it. It will be very interesting to see the effects.
MS: How well can the situation in Dar es Salaam be generalized? If we drew the same maps for other cities of the same size, would it look similar?
LMJ: Accra is similar in many ways. I can’t compare with others.
MS: What lessons can other African cities learn from your findings about Dar es Salaam and accessibility issues?
LMJ: One aspect is methodological: that free road network data from, for example, OpenStreetMap are quite good and can be used to map and analyze scenarios. The study pinpoints accessibility levels in different areas. The discussion addresses the consequences of an apparent lack of ability to coordinate and implement city-wide traffic plans, and the apparent lack of ability to implement plans for more sustainable urban development. It is very expensive and nearly impossible to “retrofit” the necessary transport infrastructure.
Maitagorri Schade is an editorial intern with UrbanAfrica.Net. She is an urban traveler and scholar who is working toward her master’s degree at UC Berkeley and has a passion for informal transportation and community development in the global South.
Image via wikimedi commons.
Read older posts from this section