How bad is traffic in Lousiville Kentucky during the Kentucky Derby?

My friend is going to be traveling through Louisville Kentucky May 3rd, and is concerned about increased traffic during the Kentucky Derby. He will be taking I64 from east to west, going through late morning/early afternoon. Can anyone give a heads up as to what he can expect/any faster routes to avoid the main area of the derby, from the map it looks like its right off I64? Thanks