I-94 is a major east-west highway. I-94 has three lanes in each direction from Ann Arbor to Detroit but suddenly reduces to two lanes in each direction at Ann Arbor city limits. As a result, traffic is typically slow and congested. Some list of ways to find out ahead of time what's up.
The MDOT Drive Interactive Map shows freeway speeds and construction. MDOT has not instrumented any Washtenaw County roads with speed sensors, but you can start to pick up its traffic reports at about Belleville.
The Yahoo interactive traffic map for the area shows incidents and speeds on not only I-94 but also other major and relatively minor roads; it is powered by TrafficCast.
The Google interactive traffic map for the area has comparable coverage to Yahoo; it has more detail for city streets, and less detail for county roads.
The Bing traffic map is powered by Traffic.com; it's primarily freeway coverage, plus notices of local construction.
I-94 expansion
The routing of I-94 through Ann Arbor is only two lanes, when the major roads nearby including I-94 through Ypsilanti and west towards Dexter are wider due to a belief that making auto-transportation as inconvenient as possible will force frustrated motorists to use public transit.