The A109 Road (also called the Mombasa Road) from Nairobi to Mombasa is 290 miles but that road was probably not there in 1961. Looking it up gave me the distance between the 2 cities, however. Travel then was much more likely to be done by train. In 1901, because of the importance of Mombasa as a port city, the British completed the building of a railway that stretched from Mombasa to Uganda and WENT THROUGH NAIROBI. Not a long trip between the 2 cities on a train. At 50 mph, the trip would take less than 6 hours. A pregnant girl could easily make that trip. That’s why the majority of evidence pointing to Mombasa as the birth place (good hospital for whites, the possible present of Obama Sr. there at the time, etc.) is not a logistical problem.
There are some other plane schedules - one for S. African Airways included at this link:
http://www.freerepublic.com/focus/news/2306351/posts?page=8573#8573
One of the sources I used for the railway information is at this link:
http://www.africatravelling.net/
And a bit later (can’t remember dates, darn brain), one of the doctors listed on Inspector Smith’s Kenyan BC lived very close to 0bama Sr in Mombasa.
I hope I’m remember details properly, someone will correct me if I’m wrong.