Many streets in the UK have roads which restrict drivers to a 20mph limit, but do they actually prevent crashes and fatalities, or are they just hindrances, especially as many come with speed bumps

The 20mph restriction

The 20mph speed signs are an important indicator to drivers that they are in a zone where there are schools and other institutions and ensures they have to drive with more attention and care. These 20mph zones also tend have an associated speed humps in order to reinforce the lower speeds.

But do 20mph zones really help slow people down? And do they actually help traffic flow?


Slow down

The majority of pedestrian casualties occur in built up areas; 29 of the 34 child pedestrians and 302 of the 413 adult pedestrians who were killed in 2016, died on built-up roads. But, according to The Royal Society for the Prevention of Accidents (ROSPA), 81% of car drivers exceed the speed limit on 20mph roads and 44% exceed 25mph.

However, while in 20mph speed limits you may still be able to speed, 20 mph zones make it a lot harder to push above the limit. The purpose of 20mph areas is to create conditions that where drivers feel like driving at 20mph is a natural thing to do, as a result of traffic calming measures or the general nature of the location (like a school).

When looking at a road that is 20mph, most of us won’t know whether to expect traffic calming measures like speed humps, central islands or chicanes or whether it’s just the speed limit. However, it’s only 20mph zones that have traffic calming measures. 20mph speed limits are only generally used in places where average speeds are already low (below 24mph)

The principle with 20mph zones is that traffic calming slows vehicles down to speeds below the limit, and in this way the zone becomes self-enforcing. All the traffic calming programmes are supposed to work in partnership to reduce speeds and improve the overall environment, meaning there can be significant difference between schemes.


Reducing traffic flow

Alongside keeping speed down, 20mph zones are said to reduce traffic flow in the area. A TRL review of 250 20mph zones across England, Scotland and Wales indicated that traffic flow in these zones reduced, on average, by 27%. However, flows in surrounding boundary roads increased 12%. Another report by Davies Gleave suggests that 20mph speed limits reduce traffic by 5.2%, while traffic calming measures reduce it by 13.4%.

What is also of note is that an increased amount of 20mph zones and speed limits will also increase the amount of cyclists and walkers, meaning that for those of us who have to use a vehicle, there are less motors on the road. Reducing traffic volume is in direct correlation to lowering cyclist and pedestrian injuries, so reducing traffic volume has the potential to improce cycle safety, pedestrian safety and road safety in general. Overall, traffic is reduced in 20mph zones, but its impact varies across areas, depending on their particular characteristics.



While 20mph limits can be frustrating, and 20 mpg zones with speed bumps can feel like they are damaging your vehicle, the overall increase in safety by implementing and following their speed limits means that your driving will be safer, both to you and those around you -  whether that’s cyclists, pedestrians or other road users.