Traffic & road safety for 20mph

The facts and official advice on traffic and road safety that are needed for a 20mph zone

Moving people and goods along roads is essential to the economy of the country. The road network is organised into a hierarchy of Motorways, Primary, A, B & C roads, etc. Apart from motorways, all roads serve a variety of road users such as drivers, passengers (bus, taxi, car) motor-cyclists, cyclists and pedestrians, including people with disabilities and children.

Road accidents mostly happen when a driver makes a mistake, such as when reacting to turning traffic or cyclists and pedestriansWhat drivers see and understand in order to react safely is governed by their vehicle’s speed. Traffic speed can be reduced by legal speed restrictions, traffic calming and works on or near the road that help drivers to slow and take more care.

To see what could be improved in your area, first look at traffic flows and speeds as well as the frequency and severity of accidents as part of a local traffic and road safety check.


The road network

Roads are organised into a strict hierarchy. At the top is the motorway network for fast long distance travel and at the bottom small residential cul-de-sacs where vehicles might share the road space with local people on foot. Between these extremes there are four national categories (Primary, A, B & C).

A driver’s road atlas gives an instant feel of the road hierarchy in any location. The A-Z series for example helpfully shows the hierarchy as Motorways – blue; Primary routes – green; Class A roads – red; Class B roads – orange and Class C roads – white. Many satellite navigation systems use all but Class C roads for longer distance journeys.

Road hierarchy shown in colour


Road users

Apart from motorways, all roads serve a variety of road users such as drivers, passengers (bus, taxi, car) motor-cyclists, cyclists and pedestrians, who include people with disabilities and children.


Accidents involving turning traffic

A straightforward crossroads has thirty two places where vehicles slow to turn, cross the path of other vehicles or join another flow of traffic. Each one is potential place for an accident


Accidents involving cyclists and pedestrians

In addition to avoiding other vehicles, drivers need to react to cyclists in the road. Cyclists vary. Sports cyclists can cope with almost any road conditions. But others are, or feel, very vulnerable. Typically they suffer when someone else, usually a driver, makes a mistake. Cyclists often do not realise that, because of their slower speed, all round vision and hearing, they are far more aware than drivers of what is happening in the road.


Pedestrians prefer to cross a road directly to a destination in a straight line. To use a formal zebra crossing usually involves a detour which leads many pedestrians deciding to or being obliged to walk in the road. The result can be seen in the national statistics of road accidents involving pedestrians on urban main roads.

Pedestrians find it difficult to cross a road where fast traffic can effortlessly turn across their path


What drivers see and understand

Over hundreds of thousands of years, humans have evolved to run and hunt, not sit and drive fast cars. To help in hunting, our eyes can focus clearly within a 2 degree spectrum and also be generally aware of what is going on across 180 degrees.


To see the wider picture clearly, our eyes scan the whole scene at the rate of about three eye movements a second. You can see people do this as they read a book.

When we drive, there is a limit to what we can see and understand. Three eye movements per second, at 30mph, equates to one eye movement every 13.5 feet. If a driver looks away from the road for two seconds, they are unlikely to see anything else on the road while they travel 80 feet. This is sufficient to fail to see a child or cyclist in the road.

To compensate for the considerable limitations of the eye, the brain fills in the gaps, based on past experience and make assumptions so that drivers can usually understand correctly what is ahead. Experienced drivers are good at looking out for the right things.


Experienced drivers become very good at looking out for the right things. But occasionally, though something is plain sight, the brain does not register it. Known as inattention blindness, something that is unexpected is not seen, even if it is large and colourful, or even a cyclist.


Effect of vehicle speed

Assuming that the driver can see and understand a hazard, they still need the react safely. The distance taken to stop has many factors: driver’s reaction time, the quality of the brakes, road surface and most importantly, the speed of the vehicle. Drivers react more slowly to an unexpected hazard than to an expected one. Other factors for reaction are age, tiredness, and the influence of drugs and alcohol. Although the distance taken to react is proportional to speed, the distance taken to brake is quadrupled. Travelling at 20mph will have a braking distance of 6 metres whereas travelling at 40mph will have a braking distance of 24 metres.


The proportion of drivers that keep their speed to 20mph in a zone, is still being assessed. The current series of 20mph zones in Oxfordshire will be carefully monitored.

There are two legal approaches to putting 20mph in place. The first is a process affecting a whole highway authority area that becomes lawful in a specific locality as soon as the new signs can be seen. A second approach deals with individual locations as separate zones exhibitions with its own public consultation process.

Oxfordshire Count Council has opted for the second approach. The legal notices, consultation documents are detailed responses for the first trial at Cuxham village are very comprehensive.

Compliance with the new speed limits will be reinforced if the mooted Intelligent Speed Assistance (ISA) is adopted by the UK government. It is scheduled for adoption across the European Union in 2022 for all new cars. In effect, unless the driver overrides it, the speed of a vehicles will be kept to the legal limit.

Proposed changes to the highway code will also require drivers to reduce their speed, take more care and alter their attitude towards cyclists and pedestrians. A new hierarchy of road users would ensure those who can do the most harm, such as the drivers of cars, vans and lorries, have the greatest responsibility to reduce the danger they may pose to others: cyclists and pedestrians.


Traffic calming

Road humps and making the road narrow are conventional works to calm traffic. They usually need to positioned at regular intervals along a road to be effective and keep speed down. They also need warning signs so that drivers are aware of them. But there is an alternative approach.

Conventional traffic calming may function well but tends to appear unnecessarily ugly in its surroundings


Help drivers to take more care

Drivers also adjust their speed according to how safe the road feels because the immediate area the road passes through is spacious or cramped.

It is possible help drivers to take more care changing the nature of the road as well as the immediate area the road passes through by various forms of landscape that fit seamlessly into the character of the town or village. New trees, hedges, verges, local art and artefacts would be part to local place-making and health and wellbeing programmes.

A courtesy crossing at Bury St Edmunds fits well into the historic street scene and also calms traffic


Traffic & road safety check

At the start of any local study into the advantages of a 20mph speed limit would be a thorough understanding of the existing conditions.

The basic statistics for a particular location along a road are flow and speed of traffic and number and severity of accidents.

Having noted the traffic and road safety records for a specific location, bring them, together with the place and health & wellbeing checks, to see how to get the most rewards from your own 20mph zone.

Delivering a positive outcome will also depend on the local highway and traffic authority and of course on political leadership and where necessary on the design of traffic calming.

References: 20mph encourages cyclists, Surrey University; 20mph reduces total accidents and severity of accidents, Rospa