The cover of Raising Steam is almost a spitting image of that of Snuff, down to the color palette, the general angle of the composition (facing left viewed straight on) and the central image of someone driving some kind of motor-assisted vehicle.
I love Kidby's work, but one wonders whether he was forced to execute a design idea thrust upon him by the publisher and its marketing department. "Oh, we sold a million copies of Snuff with a cover of Vimes steering a boat through some kind of chaotic scene, so it's obvious that we need this same kind of image to hook new readers. So just recycle the same concept with a train in it instead."