With the growing awareness on environmental protection, the reduction of fuel consumption and carbon dioxide (CO2) emission have been receiving considerable research interests. With the advances in vehicular ad-hoc network (VANET) technology, a green driving suggestion system is proposed to minimize the carbon emission by enhancing the intersection throughputs and providing drivers the best-economic driving suggestions. The idea of this work is to let the signal controllers (with built-in RSU) broadcast the signal countdown message and waiting queue information to the vehicles nearby the intersection, extending the range of drivers' visual contact to the signal. With these information, on-board unit (OBU) can determine the best economic driving speed and provide drivers' suggestions while maintaining the max throughput within a cycle time. The goal of this work is to demonstrate the advantages of reducing vehicles fuel consumption as well as CO2 emission by minimizing the unnecessary acceleration, brakes and stops. Simulation results vividly shows that CO2 emission can be reduced by 4 percent to 20 percent under different vehicle per hour (vph) cases following the proposed scheme.