Tunnels are usually built in rectangular, circular, and horseshoe shapes. Studies in this field include works of authors such as Park et al.

The most common shape for modern tunnels is the circular or "round" profile, primarily because it is the most efficient shape for withstanding the immense external pressure from soil or rock. Circular tunnels are almost exclusively created by Tunnel Boring Machines (TBMs), which use a rotating cutting head to excavate a perfect cylinder. For road tunnels, a "horseshoe" or curvilinear shape is often used, featuring a flat floor (invert) for the roadway and an arched roof to distribute the weight of the mountain above. This shape is common in tunnels built using the "drill and blast" method or the New Austrian Tunneling Method (NATM). In urban settings for subways or utilities, you might see rectangular "box" tunnels, which are typically constructed using the "cut and cover" method. While the circular shape is theoretically the strongest, engineers choose the profile based on the construction method, the geologic conditions, and the specific clearance needed for the vehicles passing through.