- As Nairobi looks to ease its traffic, the media often claim it’s the second most congested city in the world.
- The claim’s main source is an online survey that polled only 29 people over three years – and only 10 in 2017.
- As the city looks for traffic solutions, accurate data will play a big role in making policy.
Other options include introducing car-free days and a rapid bus system.
Less time in traffic would appeal to despairing Nairobians, who spend hours on the road.
But is the city of 4.7 million people the second most congested in the world, as the media regularly report?
Data from Serbian traffic index survey
Reporters often quote a traffic index run by Numbeo.com, a website hosted in Serbia. It describes itself as the world’s largest database of user-contributed data, and grades cities on indicators such as the cost of living, traffic and crime.
To rank traffic in cities, Numbeo provides “online software which allows users to compare their time and distance spent in traffic”.
Nairobians typically spend 56.43 minutes in traffic, according to the website’s most recent index. This places it first in Africa, and eighth out of 208 cities.
‘Very small’ sample
In the last three years the city has ranked between third and 12th globally.
When Africa Check asked about his data, Mladen Adamovich, the website’s chief executive officer, said 7,791 people across all cities took the survey in 2017.
For Nairobi, there were “only 29 contributions in the past three years,” he said, 10 of them in 2017. This “sample is indeed very small”, Adamovich added.
Online survey not random
Basing the traffic index on an online survey would create inaccuracies, Dr Maia Lesosky, a public health and statistics expert, told Africa Check. She is an associate professor at the University of Cape Town.
“Any ranking based on a non-random sample of 10 (or even 29) will be subject to a great deal of random noise and is not likely to be accurate,” Lesosky said.
Without a large sample, an online survey would be a poor way to collect commuter data, she said. This was because the sample was “non-random, meaning only those with an internet connection and interest in the topic will fill in the survey”.
‘Quite a lot of data’ needed to rank city traffic
Lesosky said traffic congestion was usually measured using indicators like the ratio of cars to people, the average distance travelled and the time spent below a certain speed.
“To accurately rank cities, one would need to collect quite a lot of [this] data,” she said.
People often overestimated the time spent in traffic, Prof Zachary Abiero-Gariy, the dean at the school of civil, environmental and geospatial engineering at Jomo Kenyatta University of Agriculture and Technology, told Africa Check.
He suggested Nairobi both review its land use and current radial road layout – where all the main transport routes flow into the city centre – and improve its public transport.
Collecting data on Nairobi’s traffic no easy ride
Other attempts to rank Nairobi’s traffic have also run into data trouble. In 2018, the analysis firm Mercer ranked Nairobi 186th of 231 cities in its 2018 Quality of Living survey. Although the survey considered traffic jams, it did not publish a specific traffic congestion ranking for Nairobi.
The US firm Inrix runs a global survey of traffic. The most recent covered 38 countries in 2017. Its information was drawn from anonymous GPS data provided by major car makers as well as data purchased from other sources, marketing director, Steve Dobson, told Africa Check. But such data on Africa is limited, he said, with South Africa the only country in the region surveyed. A key reason for this is the cost.
“Alternative data sources require either investment and maintenance of a network of loop car sensors, or a robust network of cameras to provide number plate recognition and analysis,” Dobson explained.
In 2011 US technology firm IBM ranked Nairobi fourth of 20 cities in its Global Commuter Pain Survey. That survey was the most recent, IBM told Africa Check.
The research was dated and would not be “used to support any current points or policies”, Kal Gyimesi, an executive with the firm, said. Gyimesi said he had “recommended to our communications team that we remove this study from our sites”.
Conclusion: No data supports claim Nairobi has the world’s second worst traffic
As Kenya’s capital city Nairobi explores ways of easing congestion, the media often report that its traffic is among the worst in the world.
A main source of this claim has been a traffic index run by the Serbia-based website Numbeo.com. The site’s owner told Africa Check that its ranking of Nairobi was based on an online survey of only 29 people over three years.
This sample was too small, an expert said. It was also not randomly selected as only people with an internet connection and an interest in the topic would likely have participated.
Comparable data on Nairobi’s traffic remains limited, adding to the city’s headache of finding solutions to the gridlock.
We therefore rate the claim as unproven.
Edited by Lee Mwiti