Arusha is a small town city with a large population.  There is no traffic control and no need for one.  Most people walk or ride on bikes.  The city is filled with noise, music, and the most awful stenches (sometimes).
 
 

Nairobi:

Nairobi is a large city.  It has many office parks and yes - electricity.  The hotels there are extravagant and wonderful.  There is much more auto traffic in Nairobi than Arusha.