In this paper we present loop (loop over orderly phases), a trace-based emulator for Vehicular ad hoc networks (VANETs). This is an alternative and novel method to evaluate improvements on VANET protocols, which relies and takes advantage of real data samples collected from an existing network. Those samples are vehicles’ geographical locations and radio reception events, which represent mobility and communication patterns of the VANET. From those samples, loop creates a synthetic environment to simulate and evaluate communication protocols on the target VANET. loop also includes an interactive mode to manage the emulation process and a visualization mode that shows different time and geographical-dependent aspects. The development of loop was motivated by the need of an non-intrusive methodology to intensively analyse and deterministically compare the impact of several strategies for communication protocols and all their possible variations in a realistic scenario, both in terms of mobility and radio communication opportunities. Namely, we created loop to evaluate the impact of adding security features to the routing control plane of an VANET. Since the VANET includes hundreds of vehicles, the computational performance is critical to speed-up evaluations. With loop we were able to perform complex, multi-variable performance evaluations of 24 hour periods in durations ranging from 6 up to 30 minutes.