Core: Speed signs A: maximum, matrix sign, advisory and zone

The A-sign category (Book p.238) regulates speed with five codes. A1 is the classic round maximum speed; whoever drives faster violates the law (mandatory compliance with an order/prohibition sign). A2 closes that zone. A3 is not, as often assumed, the advisory sign — A3 is the electronic signalling sign (matrix sign) above the lane, which thanks to the law has exactly the same binding status as a fixed sign. On some stretches (for example during congestion or roadworks) the matrix sign shows a lower number than the fixed sign next to it; the law settles that: the lower of the two numbers applies, regardless of which sign looks more 'permanent'. A4 is the blue rectangular advisory sign: a recommended speed for safe passage of the road section (for example in a sharp bend), but not mandatory — ignoring it does not result in a fine, though it is unwise if the bend genuinely calls for that number. A5 closes that advisory. If the word 'zone' appears above an A-sign, the sign applies not only at that one spot but throughout the ENTIRE indicated area, until the matching end-of-zone sign appears — even past every side street without a new sign.