There has been a general relaxation (wrongly, IMO, as it gives them the opportunity to create enforcement honeypots) in the requirements placed on highways authorities to signpost speed limits. The other issue that makes knowing whether or not you're driving on a road subject to a 20mph limit "difficult" from a driver's point of view is that the requirements for signage differ according to whether the road is the subject of a 20mph speed limit or is part of a 20mph zone. The differences are that:
- 20mph limits are roads where the speed limit has been reduced to 20mph but there are no physical measures to reduce vehicle speeds within the area. Drivers are alerted to the speed limit by a combination of terminal signs at the start and end of the limit and with 20mph speed limit repeater signs. The original guidance was that the layout and use of the road must also give the clear impression that a 20mph speed or below is the most appropriate but that seems to have gone out the window;
- 20mph zones use traffic calming measures to slow vehicles to speeds below the limit, and in this way the zone becomes ‘self-enforcing’. Speed humps, chicanes, road narrowing, planting and other measures are used to both physically and visually reinforce the nature of the road. A driver is alerted to the limit only by terminal signs on entry to the area, and there are no repeater signs within it.
Over time, and with the relaxation on the requirements for signage, there has been a blurring of the two different types (20mph limit and 20mph zone) with 20mph limits sometimes not having regular repeater signs and no other indication that 20mph is the maximum permitted speed, and 20mph zones having no (or infrequent/inconsistent) traffic calming measures while those physical features (humps, chicanes, etc.) are often present in 30mph limits. IMO, this is totally unsatisfactory and shows scant regard for the principle of fairness in legal matters.