One-way streets are designed for traffic to move along them in one direction. Motorists are made aware of the direction of flow with one-way street signs and arrows painted on the road surface.

‘No entry' signs are also often erected to prevent drivers from entering the road from the wrong direction.

It's not uncommon for junctions to be laid out in a manner that dissuades traffic from going against the flow.

What do one-way street signs look like?

One-way street signs are formed of a blue disc with a white arrow denoting the direction of travel.

Why do one-way streets exist?

At a local level, city or county authorities might enforce one-way streets for a number of reasons: to prevent drivers from making shortcuts (known as 'rat runs'); to free up extra space for residents to park; to create more width for cyclists; and to enable traffic to move more quickly and safely in the chosen direction.

One-way streets may also be enforced because there is limited space for two vehicles to pass.

How effective are one-way streets?

One of the key ideas behind one-way roads and streets is that it reduces the chances of a scrape because there is only one stream of traffic, not two.

While this may increase safety, it may also encourage motorists to drive faster because there is no oncoming traffic. However, higher speeds may increase the chances of hitting a pedestrian, a cyclist, or someone's pet.

Another disadvantage is that emergency vehicles may need to take a longer route to reach their destination.

Keeping traffic moving

A local authority may sometimes need to decide between setting up a one-way road and improving overall congestion levels. For example, while a one-way street may help locals with extra parking space, it may add to jams or slower traffic elsewhere.

An alternative route must be available

One-way roads are only set up in residential areas where another route is available.

Do one-way streets apply to cyclists?

In general, cyclists must obey one-way street signs, just as motorists must. However, in some areas - for example, Bristol - 'cycle contraflow' schemes are set up, allowing cyclists to move in the opposite direction. This is to ensure cyclists don’t need to take circuitous routes and to improve access to cyclists in general.

What limitations are there on one-way streets?

According to Essex Design Guide, around 100 dwellings is the limit for a one-way street - otherwise residents at one end of such a street may be forced to take a longer route which would otherwise have been reached more quickly - thereby frustrating people living at one end of the street.

The Traffic Signs Manual states that one-way streets must be clearly signposted at entry, exit and side junctions. Direction arrows must be painted on the road at 30m intervals, reminding drivers of the direction of flow.

When there are substantial intervals between side junctions, reminder signs should be erected for the benefit of those entering the road from frontage premises. These must be placed alternately on each side of the road, with a maximum distance of 100m between one-way signs on the same side of the road.

How wide must the carriageway be on a one-way street?

One-way streets must have a minimum width of 3.7m - which is less than a regular lane on a two-way road.

Are one-way streets popular?

A common complaint with one-way roads is that they encourage speed. Naturally, traffic moving at higher speeds poses an additional risk to children and residents in general. It has also been suggested that for this reason properties on one-way streets may fetch a lower price than comparable local properties on two-way roads.

On the other hand, residents may have more room to park and traffic congestion may be improved.