For models of the use of advanced travel information services (ATISs) and their effect on traveler behavior to be realistic from a behavioral point of view, conceptualizations of travelers' perceptions of the value of information must be valid. This paper presents a formulation of perceived information value based on the idea that travelers face different types of uncertainty when choosing from and executing travel alternatives, such as routes, travel modes, and departure times. Notions of Bayesian updating are then applied to represent the effect of singular messages from an information service. Acquiring information is deemed valuable to the extent that travelers expect, on the basis of the information received, that their update in perception results in a decrease in the levels of uncertainty they face. Numerical examples that are presented aim to verify the derived measures for uncertainty and perceived information value. This is done by varying proven determinants of uncertainty and ATIS use and investigating the effects on the derived measures for uncertainty of choice and execution and on perceived information value. It appears that trends that occur in the measures developed correspond to common intuition and empirical evidence from the literature on ATIS use; this indicates a certain degree of behavioral validity of these measures. In future research, these measures will be used in simulation and model estimation and applied to study a variety of trends in travelers' use of information services.