I’m not debating the presence of using 20 mph as a speed limit in urban areas, that is not the point of this article. I am writing to differentiate between 20 mph Zones and 20 mph Limits, as plenty of signing practitioners still get this wrong. Here is a brief overview of the history and differences between the two systems and what I feel would be better.
A brief history
Originally, 20 mph was only permitted as a speed limit if part of a self-enforcing Zone. These were first trialled in 1991 in Kingston-upon-Thames, Norwich, and Sheffield having been given consent to do so by the Secretary of State. At the time, any speed limit lower than 30 mph had to be specifically authorised. These Zones contained numerous trials of differing traffic calming measures to ensure that the limit was adhered to as the intention was to reduce child casualties in residential areas.
In 1999, an amendment to the law permitted the use of 20 mph Limits without consent from the Secretary of State. This now meant that there was a two-tier system of 20 mph Zones, intended for residential areas and heavily self-enforcing with vertical or horizontal traffic calming features; and 20 mph Limits, intended for locations like town centres which did not warrant traffic calming but reduced speeds would be beneficial to provide a better public realm experience. An area covered by a 20 mph Limit could have vertical or horizontal traffic calming features but these were not mandatory, and had to be signed separately as they would in a regular 30 mph area. What it did have to have, unlike a Zone, was repeater signs like 40, 50, and (on dual carriageways) 60 mph limits.
However, all guidance tended to steer authorities away from Limits as research demonstrated reductions in traffic speeds were often negligible and could bring the speed limit into disrepute. They were seen as only effective where traffic speeds were already 24 mph or lower. This meant that authorities were generally still installing expensive Zones with their self-enforcing features until the 2011 amendment TSRGD was issued.
The amendment changed the approach to 20 mph Zones. Previously, self-enforcing traffic calming in Zones had to be at prescribed maximum intervals, otherwise the Zone was effectively invalidated. This was scrapped, and only a single feature would be needed for the entire Zone to be compliant with the law. The amendment also redefined repeater signs and road markings as traffic calming devices, meaning a 20 Zone could have repeater signs but no horizontal or vertical devices. This also meant there is the now bizarre situation where a 20 mph Limit adjoins a 20 mph Zone and a pair of regular terminal signs saying 20 mph are placed back to back with the 20 Zone entry sign because otherwise the Zone is invalidated.
So, to summarise:
20 mph Limit:
- Start of Limit signed with regular Dia 670 sign; it may be part of a gateway sign provided it is designed in accordance with TSRGD
- Repeaters must be used in accordance with TSRGD
- Physical traffic calming features are not required but may be used; if they are warning signs in accordance with Traffic Signs Manual Chapter 4 are required
- They work best when speeds are already below 24 mph
20 mph Zone
- Start of Zone signed with Dia 674 sign and terminated with Dia 675; this may include a slogan or image on the entry sign provided it is designed in accordance with TSRGD
- Must be self-enforcing through the use of traffic calming features
- Repeaters are not required but may be used as a traffic calming feature
- They work on roads with previously higher speeds due to the very nature of physical measures
This is not a Limit, despite someone cover-plating the word ZONE! This limit is technically unenforceable as this is no longer a prescribed traffic sign.
This is a Limit, using permitted Gateway type signing.
The problem is, as you can see, there is now virtually no practical difference between a Zone and a Limit. Yet if you sign one incorrectly you open up all kinds of legal loopholes.
Quite simply, we do away with 20 mph Limits and sign them all as Zones. The inconsistency has no value to road users, it confuses people in charge of putting signs up, and brings the system into disrepute. In order to further reduce the amount of needless clutter on the roads I’d also argue that any road that warrants speed humps should be 20 mph so we can get rid of the hundreds of needless warning signs for them.
Where physical measures are used a supplementary panel to the Zone entry sign would be required as shown above.
In the meantime, the current unsatisfactory mess looks set to continue, which is unfortunate.