Evolution of Residential Highway Design in South-East England - Background

Most residential roads are designed and constructed as part of larger housing estate schemes. So I start with the question "What defines a housing estate?"

Here we have an aerial photograph from 1994 of Maidenbower on the South-East side of Crawley. Construction started in 1987 and finished in 2010

According to Crawley Borough Council’s website Maidenbower has 3355 households and 8070 residents, and measuring from GoogleEarth it covers approximately 3 square km and contains about 30km of road

This is a similar size to many small towns. So what makes Maidenbower a housing state rather than a small town?

There are many different definitions. I focus on three:

Firstly, it’s an area where the buildings are predominantly residential although it can contain local amenities like schools or shops. On its own this definition includes most towns and villages. So a second definition is needed:

It’s an area where the buildings are planned and constructed either all together or in phases. This differs from traditional towns and villages where the houses would have typically been built one by one as the community grew and evolved

A third definition is required to differentiate between housing estates and ribbon developments where lines of houses are built along existing roads, and this is that the roads are planned and constructed as part of the housing estate

There are a number of terms that can seem interchangeable, when strictly speaking they’re not. Based on the book "Roadwork Theory and Practice" I use the following definitions in this presentation:

A highway is a route along which the general public have the right to travel

A carriageway is the bit in the middle used by cyclists and motor vehicles

A road is a route comprising of a carriageway with or without footways, verges and cycle tracks along one or both sides

A street is a road in an urban or built-up area

A footpath is a route for pedestrians only which does not run alongside a carriageway – for example it can cross fields

A footway is a route for pedestrians only which does run alongside a carriageway

The pavement is not just the bit along the road edge used by pedestrians, but it refers to the structure of any hard or paved surface, including the carriageway and cycle tracks

A cycle track is a route for cyclists. It can be alongside a carriageway, or independent of a carriageway, and it can be shared with pedestrians or segregated from pedestrians

A cycle track is not the same as a cycle lane which is usually part of the carriageway, set out with road markings or a different coloured surface

When focusing on key factors that need to be considered when designing housing estates roads, these factors can be split into two groups:

"Soft Considerations" are intangible factors which we cannot design directly – for example I cannot design a journey, a person, or a transport choice – but they will be influenced by our road design and I’ve shown them as overlapping circles as they are all interconnected

"Hard Considerations” are the things that can be controlled by the highway designer (and are discussed below)

Thinking about soft considerations, there are different types of journey:

Internal Journeys start and end inside the housing estate. For example if the estate includes a school then children going to and from that school are making internal journeys

An example of External Journeys are rat-runs. They start and end outside the estate but pass through it

It is easier for our design to influence internal and external journeys - for example a circuitous route will deter rat-runs

An example of Outgoing and Incoming Journeys is residents from the estate commuting to and from workplaces outside the estate

We also need to consider the needs of non-residents' journeys. For example milkman and refuse collectors will make internal journeys from house to house, and visitors and the emergency services will make incoming and outgoing journeys

We need to ensure they can find their way around the estate easily, without getting lost - or lives could be lost

Thinking about people:

Most road accidents involving pedestrians occur when people cross the road. So we need to design crossings to maximise pedestrian safety

We can include tactile paving to help those with impaired sight, and sufficient visibility along the road to help those with impaired hearing see approaching vehicles

We can also design footways to be wide enough for people with impaired mobility in wheelchairs to travel along the footway unhindered

The Young are particularly vulnerable. Statistic show that half of road accidents involving children under 5 years old happen within 100m of the home. So we need to consider the safety of children playing in the streets

Impaired ability doesn’t just apply to the elderly. Children listening to music on headphones, or texting each other, will often have a temporary equivalent to impaired hearing or sight. So we need to consider this aspect near schools as well

Transport Choices can be summarised by dividing them into four groups:

The top group - people on foot, including with prams or pushchairs, users of wheelchairs or mobility scooters and cyclists - is the most vulnerable. So our design needs to maximise their safety

For the second group - motorbikes, cars, vans and taxis - we need to consider how to control their speeds

We need to ensure that vehicles in the third group - buses and lorries can get around. This is typically done using computer software to carry out swept path analysis

The last group - emergency vehicles needs to be able to get to its destination as quickly and safely as possible. So we need to design an understandable layout

As an example of all three areas overlapping if the housing estate includes a school, then a well designed, safe cycle track can encourage children to cycle to school

If, however, the cycle track is poorly designed or in the wrong location then parents could be more likely to drive their children to school

Hard Considerations are things that can be controlled by the highway designer. There will be many such considerations, but for this presentation I focus on just five:

Starting with topography, if we design a road’s vertical alignment to follow the existing topography this can minimise earthworks cut and fill, and reduce construction costs and carbon emissions from site vehicles

We also need to avoid steep gradients as this can deter walking and cycling

So don’t locate schools or shops at the highest point on site, as this will deter walking or cycling to the school or the shops, and instead lead to increased car usage

For Drainage we need to remember that curvy roads need more manholes than straight roads, and we want to avoid a vertical alignment that requires deep manholes and pipe runs

This is because more manholes and deeper pipe runs mean greater construction costs

We can no longer assume that all storm drainage will go off site. We need to consider sustainable drainage systems (SuDS) like swales and balancing ponds, or storage systems like oversized pipes and buried crates to attenuate sudden volumes of water from storm events

We also need to intercept and control onsite pollution. Dripping motor oil, tyre rubber dust, brake dust may seem trivial individually, but when compounded across a large estate they can create a threat to the natural environment/ecology

For foul drainage we can also consider including small on-site treatment works in our designs

For Aesthetics and Ecology we need to maintain existing mature trees and hedgerows wherever possible or create new wildlife corridors

This helps wildlife and biodiversity and creates a visually attractive housing estate

By carefully locating and aligning junctions we can maintain views and vistas, such as far away hills or valleys, or local features like a church spire

Also the appearance or over provision of street furniture (such as road signs, litter bins, benches, street lights etc.) can affect the aesthetics

We need to provide footways and cycle tracks with sufficient width for both buried and above ground utilities

Gas and water supplies prefer straighter roads and looped layouts as opposed to curvy roads and cul-de-sacs or dead-ends

Inspection chambers or drawpits for telephone and electricity are often required at junctions. So, including more junctions in a design can mean more chambers or drawpits and therefore greater construction costs

We must also consider the needs of newer types of utilities such as fibre-optic broadband, cable television, or district-wide central heating

When services are routed along footpaths or cycle tracks remote from roads, sufficient space is required for a service strip for future access and maintenance

Finally, road surface materials must be suitable for ground conditions and future vehicle loading requirements

Differing surface appearances, like different colours or paving blocks instead of blacktop, can help delineate between zones on an estate

Ease of use by pedestrians must considered. Materials must not be slippery when wet, nor likely to create trip hazards

We need to consider costs and availability of different materials, like purchase and maintenance costs, and environmental costs – recycled material as opposed to materials from finite resources