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In studies of turbulent boundary layers at high Reynolds number, the term “roughness transition” is generally an implicit reference to the case of a streamwise step-change in roughness length (whether the roughness length is associated with surface fluxes of momentum, temperature, humidity, or some other quantity). This roughness configuration and flow response has received broad attention. Here, in contrast, we consider turbulent wall-bounded flows over transverse roughness transitions using large-eddy simulation. This is accomplished simply by aligning the boundary layer freestream direction parallel to momentum roughness length transitions, instead of perpendicular. In the present cases, the bounding surface is composed of two “high roughness” strips placed between three “low roughness” strips. The influences of two parameters are evaluated:(1) λ, the ratio of the high roughness length to the low …