Hardscape -vs- Softscape Under an Overpass

[talllguy]

I am wondering why some jurisdictions use hardscaping while others use softscaping or no landscaping whatsoever underneath large overpass viaducts / bridges.

When I talk about hardscaping, I'm referring to paving the entire area with concrete, using large rocks, or some other engineered solution versus leaving it just dirt. Typical ground covers like grass don't grow well in full shade, so when the area under the overpass is bare earth, this may not be by design.

I'm curious because engineering and building a hardscape costs money. Leaving the bare earth does not. Is there an advantage to paving areas under bridges?

[DaBigE]

Easier for wind to displace the dirt if left softscaped?

[johndoe]

Erosion risk?

We commonly call it "slope protection" here, so I think he's on the right track.  The older practice seemed to be paved concrete slopes, whereas now they seem to prefer rocks.