One of the important characteristics of commuting is the fact that it is a relatively high-frequency trip taken by travelers at similar times. Transportation professionals and others often refer to this resulting pattern as rush-hour or peak-period travel. Historically, commuting to and from work has defined these peak travel periods, which traditionally take place during weekday mornings and evenings as the workforce travels to and from their places of employment. These peak periods for travel define the transportation infrastructure and service needs for roads and transit systems. Understanding these peak periods and the distribution of commuting over time is important to transportation planning and forecasting.