Slan by Van Vogt, Alfred EltonHis eyes, peering ahead over the fender, saw only the long, bleak line of pavement, unrelieved by grass boulevards, hard and forbidding.
unrelieved by decorative or other features; bare, empty, or plain
I don't understand the word "unrelieved" in this use. I see it in a general sense - line of pavement with no grass boulevards, hard and forbidding; or - something with no decorative or other features. But what this word itself means in this context - I don't understand. Unrelieved from what?