Depends exactly what you're after. This will be mostly a matter of playing with specular values.
Looking at your picture, I'm guessing you're not looking for a completely uniform level of reflection over the whole surface, so using something like the ksMultilayer_fresnel_nm shader is probably a good idea, since you can use a texture with an alpha channel in your txDiffuse slot. The main (RGB) channels will be your main surface texture, then the alpha channel is a black & white image which defines the specular level, so you can fill that with a texture that describes which parts you want shinier and which parts duller. Then the whole effect is multiplied by the specular related number values you use in the shader settings (including "tarmacSpecularMultipl" !).
In case you've not already seen this, the above use (and more) is described very well in this guide. I know you're not creating a normal asphalt type surface, but the principles apply just the same.
https://assettocorsamods.net/threads/photo-quality-road-surface.834/