Whatever an all-ages-friendly city is, we are going to need more of them. Cities in the developed world have an ageing population while others have a high proportion of children. Both sectors are unfortunately too often overlooked, and we are going to need to find ways to support them. But how?

So-called 'smart city' research often makes little reference to the needs of different age groups, a serious flaw. For this reason an 'All-Age-Friendly City project' was carried out in Spring-Summer 2014 at the University of Bristol. It has just published its first results, which make clear why designing the All-Age-Friendly city is "an urgent contemporary concern", the resources that are available to us to do this, and which identify four key areas for future development:

1. creating all-age-friendly transport systems;
2. re-imagining housing;
3. encouraging encounters across generations; and
4. building intergenerational trust.

Conflicts between generations often arise over the use of resources, for example resentment by young workers of paying for the needs of older citizens in care homes etc. But this conflict is generated by the design of society and partly a function of the lack of opportunity for different generations to mix in public spaces.

If different generations are segregated there is little opportunity for them to learn to understand each other and what they have to offer. But both extreme age groups have much in common: they want access to safe public spaces and have a fear of crime; they need to socialise, face stereotyping and may be disadvantaged in the workplace.

Our challenge is to imagine a city that is capable of being all-age-friendly. The report therefore imagines four possible scenarios:

The living city

In this scenario nature is important and key values of protecting and growing are embedded throughout the city. Buildings use biomimicry while older ones have green roofs, and the city is fuelled by local, renewable energy. It is governed by representatives from all ages of life who are chosen by a lottery system.

There are no cars, which creates safe spaces for everyone to connect with each other, and there is a strong sense of public ownership in the city with public spaces designed for socialisation. Communities are consequently healthier and happier, with less crime and more community responsibility.

More education happens outside and there is a 20 hour working week for all. Children are free to move around and some time every day is spent contributing to the community and learning life skills.

The new Venice

In this scenario, a coastal city is partially flooded in 2070 and the geography has radically changed to include boat and water transport, taller buildings with hydroponics and farming intensively connected with architecture, a predominantly vegetarian and fish-based diet and energy coming from a dam and solar power.

An embedded wireless communication network manages supply and demand of constrained resources, health care (by remotely diagnosing individuals) and food supply. Older people are encouraged to fish and farm and share these skills with the younger generation; there are more apprenticeships. Family commitments are effectively swapped through systems to support trust and updates on care.

The trusting city

Here, in a decentralised city, citizenship is encouraged through the built environment of a mixed-use, high-density urban landscape. Residential dwellings, services, commercial properties and industrial building are combined across the city with no specific centre.

The community spirit, more typically found in villages, is scaled up to the city as a whole using technological solutions such as tradition technology and real-time data feeds to address perceptions of fear. There is a self-regulating system of peer-vouching, and technology to capture and measure emotional and health perspectives and respond to them.

Connectivity challenges feelings of tribalism and festivals and iconic buildings with shared public spaces support encounters between different groups.

An ubiquitous, affordable and accessible public transport system is available. Dwellings are constructed from pods and modules that are flexible and adaptable as lifestyles change.

A city of hubs

This scenario envisages the least amount of change to the current city. Intergenerational mixing is encouraged through multiple, centralised hubs of facilities. These hubs are connected not just physically but psychologically and economically. Each hub has some level of self-governing ability.

There is a balance between localism and connectivity and reclaimed public space is connected by nature-rich avenues.

The way forward

The report envisages that building trust between generations will be one of the key stepping stones towards any of these imagined futures. A trust-creating city-interface could share data that was actively positive and encourages participation in public spaces. It would challenge perceptions of fear by communicating visualisation is of how many people might have walked down a street and not been mugged, for example.

The report details a number of initiatives such as Taskrabbit and Friend of a Friend which are already trying to build trust between strangers.

One thing that came out of the workshops leading to the report was that the historic focus on city centres as a site of regeneration and cultural activity does not address the increasing numbers of young and older adults living in suburbs and outskirts of cities. It also highlighted the role of shopping centres as important social spaces used by both sectors.

Also highlighted was the way that pavements are increasingly unfriendly to pedestrians, buggy users and wheelchair users or the partially sighted, all of which need protection from traffic. The design of infrastructure can therefore be improved.

Some public spaces are also sites of tension between generations.

Modular housing or the adaptation of existing housing stock should be encouraged to create intergenerational homes. For example Accessory Dwelling Units (ADU) have been used for a long time as a solution to multi-generational living as they allow for privacy when it is required, and communal living when appropriate. The ADU is a self-contained dwelling that is annexed to a principle dwelling, often referred to as the 'granny flat'.

This was formalised with the launch of the Elderly Cottage Housing Opportunities (ECHO) project in the US over a quarter of a century ago.

It concludes with a set of definitions of the All-Age-Friendly City. It is a city that takes into account the needs and interests of all generations in its democratic processes, planning and design, characterised by:

• Representation and voice of children, young people and senior citizens in democratic processes and citizenship while recognising the heterogeneity of these groups;
• The experience and perception of safety in the city, including physical, economic and psychological safety, for children, young people and senior citizens;
• A sense of ownership of the city, in particular its public spaces, and feelings of belonging, being considered and being welcome in these spaces;
• A walkable city, supported by high quality, accessible and low cost transport systems, that encourages mobility and participation in public life;
• Integrated planning processes and service design that consider and encourage beneficial opportunities for interactions between children, young people and older adults in all areas of education, health, family and civic life.

The All-Age-Friendly City is an achievable dream. The needs and interests of children, young people and older adults are often complementary.