The most recent technique to study the behavior of tunnel ventilation is computational fluid dynamics (CFD). This approach is capable of modeling the multi-dimensional, obstructed and non-obstructed tunnels of arbitrary geometry. This paper addressed the methodology improvement for the design of ventilated road tunnels using CFD technique. A comprehensive CFD simulation has been carried out to examine the velocity, pressure and temperature distributions in the main scenario of tunnel ventilation in case of normal and halted traffic. The predicted results are used to enhance the design and evaluate the ventilation system capability to fulfill the required thermal environment inside the tunnel. The base design of tunnel ventilation system was modified to avoid the unsafe regions in the tunnel where the effects of carbon monoxide (CO) are hazard. NOMENCLATURE CFD Computational Fluid Dynamics CO Carbon monoxide k The turbulence energy LES Large Eddy Simulation MTFVTP Memorial Tunnel Fire Ventilation Test Program MVS Mechanical ventilation systems NO x Oxides of Nitrogen NRC National Research Council RANS Reynolds-averaged Navier-Stokes SES Subway Environmental Simulation SO 2 Sulfur dioxide ε The rate of viscous dissipation of turbulence energy ω The turbulence dissipation rate * Syrian Armed Forces ** Egyptian Armed Forces