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IVC (Inter-Vehicular Communications) is a key technology to realize the next generation of ITS. The authors have developed Vehicular Collision Avoidance Support System (VCASS) based on IVC in order to prevent a vehicular accident beforehand. The system grasps the relative locations of vehicles by exchanging the GPS information with each other. The system warns drivers if it estimates the possibility of vehicular collisions. VCASS can drastically reduce the potential accidents of vehicular collisions. Advanced safety technologies such as VCASS will popularize in future. However, it is hard to expect that all vehicles in the world will have the VCASS system in short time. Thus, we have proposed S-VCASS (Substitution Vehicular Collision Avoidance Support System) for mobile terminal holders (MTH), and vehicles whose drivers have S-VCASS in their MT (Mobile Terminal) will be able to work like VCASS-equipped vehicles. In this paper, we propose effective algorithms for S-VCASS in the environment of mixed VCASS and non-VCASS vehicles. S-VCASS by MT has two problems. (1) S-VCASS by MT has no detecting function of possible vehicular collisions beforehand. (2) MT has small battery capacity. To solve these problems, we propose two effective algorithms for S-VCASS. The first is to add simple position estimation by LSM (Least Square Method) to MT for the collision detection. The second is a transmit control algorithm for the power saving. By these methods, MT with small battery capacity can do collision avoidance with other vehicles. We evaluate the performances of a position estimation by LSM and a transmit control algorithm. As a result, we show that the proposed algorithms are able to accurately warn a vehicle driver.