Cycling is definitely on the increase in Norwich. There are more cycle shops, more cycle stands and, of course, the new web of pedalways is emerging on our streets. Hanging on to the coat tails of the pedalways is a move by Norwich City Council to reduce traffic speeds in the city centre to 20mph.

The proposal, which is to be decided in June, has counterparts all over the country in a campaign known as 20's Plenty for Us, founded in 2007.

The 30mph limit was set in 1934, when there were fewer than two million motor vehicles on the roads.

Campaigners believe that it is now a dangerous speed in residential areas given the vast increase in the amount of traffic.

It is claimed that the benefits of lower speed limits include better air quality, a reduction in the danger to drivers, walkers and cyclists, less congestion and increased shopping footfall. Campaigners also say lower speed limits promote health, as more people will choose to walk the streets.

There is evidence that since the introduction of 20mph speed limits in Bristol, walking and cycling are up 20%.

On the other hand, in Tuesday's Evening News, a retired traffic and road safety engineer pointed out that accidents are more closely related to speed variance rather than speed limits.

If a speed limit is set too low, it causes conflict between those drivers who will always obey the speed limit and those who continue at a reasonable, safe speed.

This may be more relevant to roads outside city centres, where overtaking and tailgating can lead to accidents. Residential areas all over the country, including parts of London, have already implemented a 20mph limit.

The 20's Plenty campaign says it is a new way of thinking – no longer about 'vehicle dominance' and more about an egalitarian principle of a citizen's right to travel on foot or on bicycle without fear.

So how would it work in our city centre? The Norwich Society has two areas of concern.

The first is about how this change is signalled.

At one time, streets were marked with repeated 20mph circular signs. Zones were heralded by square 20mph signs and had to include calming devices.

Mini-roundabouts are now classed as calming devices.

The ideal method is to design streets which clearly show drivers that they are entering a special area where slower speeds come naturally.

This can include removal of kerbs, different paving, planting of trees, provision of extra seating and diagonal street parking. With current financial constraints, resources to implement large-scale changes to the city's streets are not available.

Using signs and speed ramps can be visually intrusive and may add to noise and pollution as drivers speed up and slow down.

The society suggests using simple zone signage at the entrance to the area, but also giving people plenty of time to adjust to the new speed.

Secondly, the society considers that even 20mph may be too high a limit for some streets, such as the area of St Andrew's Street by the Blackfriars and St Andrew's Halls and Cinema City, which could become a prime pedestrian crossing route from St George's Street.

The society has also called for a re-examination of whether some streets should be pedestrianised, with traffic limited to vehicles requiring access.

Elm Hill and Princes Street are the obvious candidates as neither is essential to maintaining access to the city centre and both are so narrow that pedestrians feel vulnerable.

This medieval area should be a major tourist attraction between the shopping core of the city and the cathedral.

Then there is the problem of enforceability – not least because the vehicle that whizzes past you at 30mph may not be a car but a bicycle.