Tunnels in the New Toumei-Meishin expressway have large cross sectional areas in order to accommodate three lanes of traffic. However, the amount of heat released and smoke generated when fires occur in tunnels with such large cross sectional areas has not been studied. In this study, results of three-dimensional large eddy simulations (LES) are compared to full-scale experimental results in order to determine heat release rates from fires in tunnels having large cross sectional areas. It is shown that the maximum heat release rate increases proportionally with the fire source size, i. e. the gasoline pool area, while ventilation velocity has little effect on heat release rate. It is also found that heat release rates in tunnels with large cross sectional areas are much larger than in conventional two-lane tunnels.