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 physical traffic calming feature within a 20 mph zone. Beyond that traffic authorities may, at their discretion, place any combination of the following at 100 metre (maximum) intervals:
 * additional physical traffic calming features;
 * upright signs to diagram 670;
 * 20 mph roundel markings to diagram 1065

But in doing so they will need to carefully consider the implications for the self-enforcing nature of a 20mph zone.

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