© 2019 The Authors. Published by Elsevier B.V. In this paper, we consider a special scenario where connected (V2V and V2I) vehicular technologies are used to alert motorists when they approach a hazardous zone, such as a low visibility area, and recommend proper speeds. We present the principles of the proposed safety driving system and compare the performance of V2V and V2I communications in terms of road safety effectiveness and network communication efficiency. This performance analysis is based on extensive computer simulation experiments by adapting the iTetris platform under various scenarios. We also explore, via simulations, whether CHAA systems, based on V2V and V2I communications can potentially contribute towards eco-driving by reducing Carbon Dioxide (CO2) emissions. Our simulation results showed that our alerting system, based on V2I communication, yields better message reception rate and better safety efficiency compared to a V2V alert system. The results also show that the proposed CHAA system can contribute as well towards reduced CO2 emissions by promoting speed harmonization.