Unexpected disasters, both naturally occurring and those caused through human actions, result in severe damage to communication infrastructure. Additionally, such events are accompanied by sharp spikes in the usage of commercially licensed spectrum, when affected victims of the tragedy attempt to transmit information about themselves and capture high bandwidth data in the form of pictures and videos. We envisage cognitive radio as a candidate solution in such situations, where the devices can identify alternate frequency bands, and opportunistically use them. In this article, we describe a network architecture called EC-CRVN composed of CR enabled vehicles that provide critical wireless connectivity to both the general public and emergency responders. We discuss the application scenarios and salient features of the EC-CRVN. We describe the existing state of the art, the research challenges involved in realizing them, and a new approach of spectrum sensing using moving vehicles that reduces errors without adding to communication overhead.