Bear in mind that a city that grew to have 21 million inhabitants may not have had the infrastructure to handle the same amount of automobile and motorcycle drivers. While I was told that the train system was safe and fast, there was nothing that could be done to curb the nightmare traffic jams that could make a 1 mile drive up the street take 45 minutes.
Best advice: Plan to make an early morning of things in order to get where you need to go on time...there is always traffic, but it seems to double at 8-9am. If you aim to get to the Egyptian Museum, you may want to get there early anyway to avoid the crowds. If you are on a tour that is driving to Giza to see the pyramids, you may want to leave early before 9am.
Also be aware that the smog in the city is awful. The car exhaust especially while in traffic could give you a hacking cough for days...there is not much you can do to avoid this since if you put up the windows the exhaust manages to seep in anyhow. Don't let this adversely affect your trip! Cairo is an interesting city to explore and well worth it!