The Mombasa highway (A109) is the main road linking Nairobi and Mombasa, and for the majority of its distance (482km) runs adjacent to the Nairobi–Mombasa rail line, a branch of the historic Uganda Railway. It’s regarded as the busiest (and most dangerous) road in the country thanks to the constant stream of trucks carrying goods along it from the port of Mombasa to be distributed in Nairobi and beyond.
The largest town on the highway is the sisal-processing centre of Voi, about two-thirds of the way to Mombasa. Before and after Voi are a string of smaller highway service towns, not much more than a scruffy line of petrol stations, dukas and roadside vendors, though they provide an opportunity for a break from the hectic drive. There are, however, several wildlife-related places where you might think about stopping over for a day or two, including the Kibwezi Forest and Ngutuni Game Sanctuary – as well as Tsavo East and Tsavo West national parks.
As you travel south down the highway, you may, in exceptionally clear conditions, see Kilimanjaro, either on the stretch between the small settlements of Sultan Hamud and Kiboko, or to the west of the Tsavo River. Your best chances are in the early morning or late afternoon.