accessibility measures under alternate and counterfactual land use patterns. We find that land-use changes can enhance aggregate accessibility in Nairobi and promote a unified labor market even in the absence of transport and building investments. Section 6 concludes. The Appendix discusses methodological and data choices and limitations.

# **2 Context: Urban form and mobility**

Nairobi County is rapidly growing: Its population grew by one million people over the last decade reaching 3.1 million people in 2009<sup>6</sup> and was home to approximately 3.2 million people in 2012<sup>7</sup> . While residential development is spread out, featuring clusters of high density pockets throughout the city, Nairobi’s employment arrangement follows a highly monocentric pattern. Land use areas which are likely to host most formal jobs, such as industrial, commercial and public facilities remain highly concentrated in the urban core, with only limited activity occurring in other emerging centers. New road and highway infrastructure, higher land prices, increased rates of car ownership, and other factors appear to be fueling a discontinuous or “leapfrog” outward growth in peri-urban settlements and along major road corridors.

Small, privately-owned, and artisanally operated buses and vans, known locally as matatus, form the backbone of public mass transportation services in the Nairobi metropolitan region. Matatus and walking dominate the mode share. Eighty-three percent of all trips include walking as the major or secondary mode of travel. Forty-one percent of all trips are walking only, 42 percent involve other modes, mainly matatus (63 percent) and buses (21 percent). Only 17 percent of all trips are made without walking, among which, more than half (54 percent) are completed by passenger cars and 13 percent are made by motorcycle (JICA 2013). Compared to other large cities in Africa, Nairobi has the largest share of walking trips despite rising and relatively high motorization rates compared to other major African cities (JICA 2006; JICA 2014; Kumar and Barrett 2008).

The overall average travel time per trip in Nairobi is 47 minutes, but differs when compared by gender, age, personal income level, mode, and trip purpose. Higher earners generally make longer trips (by time), while average travel times for motorized modes hover between 54 and 60 minutes per trip (excluding motorcycles, which average 38 minutes per trip).

Traffic congestion is a growing problem in Nairobi, resulting from rapidly increasing population and the crowding of motorized traffic onto a limited street network. Indeed, IBM ranked Nairobi fourth highest in its “commute pain” survey in 2011, indicating that the city hosted one of the world’s longest traffic jams, 2.1 hours. According to the World Bank’s Kenya Urbanization Review (World Bank 2016), increasing average commuting speeds from the average recorded 13.5kph to 20 kph would save $54.1 million USD per year and decrease time spent traveling by 30 percent. Increasing average travel speeds to 30 kph would save $93.4 million USD per year and decrease time spent traveling by 54 percent.

> 6 as measured by the Kenyan Census.

> 7 according to landscan data (Bright, Rose, and Urban 2013).

5