This paper analyzes the value of highway travel time information systems. This is achieved by using notions of expected utility theory to develop a departure time selection and route choice model. The model assumes that every driver has a level of accepted lateness for his trip and some perceived knowledge of the travel times on the route. Only these two inputs support his decisions. The decision making process does not require the consideration of a complex cost function and does not involve any optimization. The results of the model are used to compute the unreliability costs of the trip (i.e. scheduling costs and stress) and to obtain the benefits of real time information systems. Results show that travel time information only has a significant value when there is an important scheduled activity at destination (e.g. morning commute trips), in case of total uncertainty about the conditions of the trip (e.g. sporadic trips), or when more than one route is possible. Systems with very high accuracy are not in better terms. The paper also highlights the difference between the actual value that information provides to the drivers and the value they perceive, much smaller. This misperception suggests limited willingness to pay for travel time information.