Cilia are organelles emanating from the surface of nearly every cell in the body playing crucial roles in cell signaling and motility. For cilium development and maintenance, intraflagellar transport (IFT) along the ciliary axoneme is essential. In Caenorhabditis elegans chemosensory cilia, IFT is driven by two kinesin-2's - kinesin-II and OSM-3 - carrying cargo toward the tip of the cilium and a cytoplasmic dynein - dynein 1b - driving the transport in the opposite direction. How these motor proteins cooperate and how their action is regulated is largely unknown. Here we apply high-sensitivity, quantitative wide-field fluorescence microscopy, which allows visualization of fluorescent motor proteins at endogenous expression levels. To this end, we have generated transgenic worms using Mos1-mediated single-copy integration of transgenes encoding fluorescently-labeled IFT-kinesins. We show that kinesins relay on the cilium structure to drive IFT: kinesin- II is the key player in the initial stage, while OSM-3 takes over further on. At the base of the tip, kinesin-II combines with tens of other kinesin-II's to form trains of motors. On the so-called middle segment of the cilium, kinesin-II motors progressively detach from the microtubules and are almost instantly transported back. At the same time, OSM-3 motors increasingly take over and transport cargo further, to the cilium tip. These findings shed new light on cooperativity of motor proteins driving intracellular transport in vivo.