—In this paper we use real data to investigate the correlation in time and space between vehicular traffic and telecom traffic in cellular networks. The analysis of such a correlation is critical to assess the feasibility of cellular network architectures where densification is achieved with small-cell mobile base stations carried by vehicles. This is an attractive possibility for the provisioning of on-demand capacity through temporary dense small cell deployments where and when needed. Our results indicate that vehicular traffic at penetration rates expected for small-cell-carrying vehicles is much more bursty than telecom traffic. Yet, some correlations between the two emerge, even when considering an entire large metropolitan area. More importantly, correlations tend to be stronger in densely urbanized areas and during high-demand time periods, i.e., where and when radio access densification is most needed. Overall, our results indicate small-cell base stations carried by vehicles as a promising and cost-effective approach to dynamic provisioning of capacity in future-generation cellular networks.