This paper proposes a route-planning method for an environment in which self-driving vehicles are widely used. Such vehicles will plan their route based on the passenger's condition, which is recognized using a biological sensor. Various carmakers and IT companies have recently developed various technologies for self-driving vehicles, Google, Inc. being one. In this paper, we focus on a technique for route planning. In particular, we discuss how to realize the avoidance of traffic congestion. Our self-driving vehicles generate a new route to avoid traffic congestion when it occurs. We adopted a time-constrained heuristic search (TCS) to which we can set the time limit in advance. If we set a longer time limit, routes closer to the optimal route can be generated. A TCS ensures that vehicles can obtain an avoidance route without stopping before entering the traffic congestion. We executed some experiments concerning the relationship between total efficiency and the diffusion rate of self-driving vehicles using our own self-developed traffic simulator. As a result, we were able to clarify the phenomenon in which a peak in the total efficiency occurs, and decreases as more vehicles generate avoidance routes. Therefore, it is not always best to generate an avoidance route, and the decision to drive along the current route without generating an avoidance route becomes important in certain cases. Thus, we propose a method in which a vehicle judges whether to generate an avoidance route based on the passenger's condition. To detect the passenger's condition, we use a sitting-pressure sensor, which can detect the movements of the passenger's center of gravity. This sensor allows us to succeed in recognizing passenger fatigue. We can therefore make certain judgments: The vehicle will go along the current route if the passenger seems to be relaxed and in a comfortable atmosphere, the vehicle will arrive earlier by avoiding traffic congestion if the passenger seems to be tired or irritated, or the vehicle will stop for a break period if the passenger seems to be significantly tired.