From Longman Dictionary of Contemporary Englishat a good/rapid/fast etc clipat a good/rapid/fast etc clipFAST/QUICKquickly Traffic was moving at a good clip. → clip
Examples from the Corpus
at a good/rapid/fast etc clip• He was walking along at a good clip, his eyes idly panning the facades of the brownstone houses.• Up ahead, a thoroughfare Traffic was going across the intersection at a good clip in both directions. 