Travel demand and behavior examine different phenomena. Both deal with personal choice but differ in many ways. Travel demand is examined at the aggregate or system wide level. Travel demand is used to forecast the future. Travel planners in the Bay Area, for instance, study travel demand to predict the future use and load on the current infrastructure. Where as travel behavior is more local, measured by individual, household or vehicle. Travel behavior studies aim to measure the attitudes and their impact on selection, flexibility and conveniences of a population. A transportation behavioralist may ask “why do people drive versus take the subway?”
So why do people travel? First, people travel because there is a demand to be in different places. People travel to be where they need to be. In this instance, travel is defined as a disutility, something people want to minimize. Second, people travel because they may enjoy traveling, like a road trip versus taking the train. People may enjoy the act of driving. Also, people travel for personal recreation or exercise. Many go on vacation to ski or hike. People inherently like to move and be mobile. Other hobbies include horseback riding, bicycling, running, etc.
Modeling is often used to untangle complex scenarios. Transportation demand forecasting is the workhorse for most metro areas. Modeling can be based on a variety of data, including large-scale travel and activity diary surveys. Diaries entries contain information like whether the participant traveled, where they went, by what means, and which route. Modeling can also factor attitude and opinion of traveling.