Travel time data becomes widely available with the deployments of location-based technologies including GPS-equipped vehicles and cell phones, Bluetooth readers, Dedicated Short Range Communication devices, etc. This change has made a shift on the existing distance or historical speed based route guidance to travel time-based route guidance. For example, commercial GP-based navigation system utilizes real-travel time data for updating en-route guidance. However, the variability of link travel times was not explicitly considered. This paper explores route viability using real-time link travel time data obtained from Dedicated Short Range Communication (DSRC) devices in Daegu City, South Korea. The purpose of this study was to quantify the quality of alternative routes by explicitly considering route travel time variability. To demonstrate the practical implication of the proposed route viability, a few origin and destination pairs were selected, the distributions of shortest travel time routes (i.e., the best and the second best routes) were generated, and the viability of the shortest routes were compared on the basis of the viability index. It was found that the shortest route based on average travel time is not always the best route due to travel time variability as such viability index will help travelers understand the quality of the routes.