In smart transportation systems, the infrastructures such as traffic lights are expected to transmit different safety messages according to the receptors (i.e., vehicle, pedestrian, platoon, etc.). The focus of this study is the infrastructure-to-platooning scenario where the lead-vehicle receives the signal from the traffic light (I2V), decodes, and re-transmits it again using its taillights to the following vehicle (V2V). Normally, the lead-vehicle also communicates with nearby vehicles to avoid the crashes and/or sharing the primary public safety information. Therefore, to enable the infrastructures and the vehicle to efficiently perform their multi-connections, it becomes necessary to know what the optimum power for the I2V and V2V links is. In this paper, we answer this question by realistic modeling of the hybrid I2V-V2V system. We first propose a new I2V path loss model considering the inherent characteristics of commercial traffic lights. For V2V link, we utilize a recent path loss model obtained with the same approach and with commercial taillights as the transmitters. Then, we obtain the SNR of both I2V and V2V links which are moreover used to derive the optimal power allocations that minimize the end-to-end BER of the I2V-V2V system. The effect of system parameters such as I2V and V2V distances, total transmit power, and system bandwidth on the BER is further investigated.