Estimation of route-level travel time distributions (or travel rates) from segment-level data is of great interest today. This paper shows how the random variable properties of comonotonicity and independence can be used in combination to develop such distributions for a wide range of operating conditions. Efficacy of the technique is illustrated using Bluetooth-based travel times collected from individual vehicles on I-5 in Sacramento. The technique offers a way that agencies and other service providers can provide credible travel time (travel rate) distributions to route guidance devices, freight dispatchers and other users who want to know about the reliability of travel time estimates for the routes they utilize.