The aim of this study is to find the critical velocity of push the smoke towards tunnel exit only. It is also aimed to find out the minimum distance between the jetfan and fire source for the smoke not to be hindered by turbulent flow environment induced by jetfans installed under the tunnel ceiling wall but to maintain the laminar state downstream flow. For the study, the scale model experiments were carried out with the PIV visualization technique. FDS, a CFD fire simulation tool was also utilized to complement the study. From both experimental and numerical studies, it was found that at least distance of 25m is required between the jetfan and fire source for the effective control of the smoke. The smoke flowed most stably when the distance is 50m. It was also found that when the distance is over 75m, the strong wind formed at the middle of the centre line of the tunnel cross section starts to break the stable profile of the smoke. It is expected the results from the current research will contribute to refine the design concept of the smoke management system of the longitudinally ventilated road tunnels.