"McLaren, Ferrari, Renault and BMW Sauber have all made very literal interpretations of the revised 2009 rules regarding the rear diffuser. All of the channels are the same height and length, with no difference in height between the main central section and the side channels. This contrasts with the designs of Toyota and Williams (see subsequent illustrations), which interpret the new regulations slightly differently."
"Toyota's diffuser makes a very interesting interpretation of the revised 2009 rules (and one that has already prompted speculation regarding its legality). By exploiting regulations that allow extra bodywork within a 150mm zone in the centre of the car, the team appear to have cleverly shaped the TF109's rear crash structure (upper red arrow) so that it effectively lengthens and heightens the diffuser's central section, which also features a very low splitter at its base (lower red arrows)."
"Like engine suppliers Toyota's, Williams' interpretation of the revised diffuser regulations is highly innovative. Much of the diffuser's central section is actually lower than the outer sections. However, clever shaping of the rear crash structure immediately below the rear light effectively creates a second central section (red arrow). In combination, the result is a central section that exceeds the 175mm height allowance that applies to the diffuser alone."