No. The reapers built the citadel as a mass relay, we humans don't have that technology. Also, nobody knew the citadel was a mass relay (only Shepard found out when Vigil told him on Ilos), and I am sure that information was also classified. So no, Nexus is just a normal base
Hang on! Just noticed something, it makes sense that the tram is moving horizontally from the Hyperion to the very centre of the Nexus where you meet Avina and the turian but when you head to the new "presidium" part of the Nexus which is the ringed part, shouldn't the tram then move vertically up or down? And wouldn't the tram rotate to avoid be upside down when you move upwards? It doesn't make sense.
