Highway Engineers specialise in the design and construction of our roads and streets, but how do they decide which is the most appropriate solution?
This resource provides an introduction to the various road and street types, the balance of place and movement, the primary function and purpose of each, giving links to design standards guidance and further information.
What is the difference between a road and a street?
The Department for Transport (DfT) in Manual for Streets (2007) gives a clear definition of streets and roads:
- Roads are essentially highways whose main function is accommodating the movement of motor traffic.
- Streets are typically lined with buildings and public spaces, and while movement is still a key function, there are several others, of which the place function is the most important.
Balancing ‘place’ and ‘movement’
‘Place’ and ‘Movement’ are the two fundamental components of street design, with place being given priority above movement. The SCOTS National Roads Development Guide (NRDG) define this relationship between ‘Place’ and ‘Movement’ as:
- “Place status denotes the significance of a street, junction or part of a street and therefore consideration of place is considered critical in the design of good transport networks.”
- “Movement is activity and can be expressed in terms of traffic volume and strategic importance of the street, or section of that street, it also considers other street users such as pedestrians and cyclists".
All roads and streets should be planned and designed from this perspective. For example, Designing Streets (2010) explain that defining the relative importance of particular streets/roads in terms of place and movement functions should inform subsequent design choices. For example:
- motorways – high movement function, low place function;
- high streets – medium movement function, high place function; and
- residential streets – low to medium movement function, medium to high place function.
When engineers design streets, there are a range of minimum standards required to guide the safe and efficient passage for various types of street users.
Manual for Streets (2007) explains that street character types in new residential developments should be determined by the relative importance of both their place and movement functions. The NRDG also states that a street layout which fails to recognise the street character types and frequency of its users is also likely to fail with regard to the wider structure of the street network.
Any street whilst considering place before movement must balance all associated functions and considerations to deliver a sustainable and adaptable outcome.
There are several types of road, which have their individual and specific functions. Designing Streets (2010) provides a summary of the individual road types:
- strategic roads – provide for major traffic movement between centres of population and economic activity on a national and regional level.
- main roads or primary streets – within urban boundaries these link traffic from strategic roads to residential streets or industrial roads. They include ‘arterial’ through routes and mixed-use, multi-functional ‘high streets’ (at least in part along their length), providing access to properties as well as other amenities. Likely to be public transport routes they require a careful balance of place and movement when improving or connecting into with new development.
- residential streets – provide access to properties and through routes within a residential area. As secondary connectors they are much less likely to be public transport routes.
- residential and service lanes – solely access to properties within a residential area. These tertiary streets could be mews, vennels, or courtyards.
- industrial roads – link multi-functional industrial/commercial premises and associated parking and service areas to main or strategic roads. When within urban boundaries some elements of Designing Streets may be applied, dependent on context and an assessment of future adaptability, but the balance is towards vehicle movement.
Other routes, not for motor vehicles:
- footways – a pedestrian route that adjoins a carriageway
- footpaths – a pedestrian route not adjoining a carriageway
- cycleways – a cyclist route that adjoins a carriageway
- cycle track – a cyclist route not adjoining a carriageway
- shared surfaces – low trafficked single level street that serves a range of user types, normally limited to residential streets where traffic speeds do not exceed 10 mph
A Motorway is a strategic road for major traffic movement between centres of population and are classified in England as Special Roads – roads where certain types of traffic are prohibited.
The Primary Route Network (PRN)
The PRN, in England, designates roads between places of traffic importance across the UK, with the aim of providing easily identifiable routes to access the whole of the country (DfT, 2012). The PRN is constructed from a series of locations (primary destinations) selected by the Department for Transport, which are then linked by roads (primary routes) selected by the local highway authority.
The PRN is a devolved matter. Several primary routes run between England and Scotland or England and Wales, meaning cooperation between highways bodies across borders is required. The criteria for defining a primary destination are purposefully flexible, in order to allow the PRN to serve the whole of the country.
All Primary routes consist of an A road or sequence of A roads, forming a continuous route between two primary destinations. All UK roads (excluding motorways) fall into the following four categories:
- A roads – major roads intended to provide large-scale transport links within or between areas.
- B roads – roads intended to connect different areas, and to feed traffic between A roads and smaller roads on the network.
- Classified unnumbered – smaller roads intended to connect together unclassified roads with A and B roads, and often linking a housing estate or a village to the rest of the network. Similar to ‘minor roads’ on an Ordnance Survey map and sometimes known unofficially as C roads.
- Unclassified – local roads intended for local traffic. The vast majority (60%) of roads in the UK fall within this category.
Standards for Highways online resources
Highways England produces standards and documentation relating to the design, construction and maintenance of highways. Documents are available free online, including:
- The Design Manual for Roads and Bridges (DMRB) contains information about current standards, advice notes and other published documents relating to the design, assessment and operation of trunk roads, including motorways. The DMRB has been prepared for trunk roads and motorways. The basis of use of these documents by local highways authorities is given in the DMRB GD 1/08. Check with your local highway authority for their policy on this matter The DMRB was introduced in 1992 in England and Wales, and following that in Scotland and Northern Ireland. Some standards and specifications have annexes specific to each devolved administration. You should contact the relevant devolved authority directly for guidance.
- Well Maintained Highways - Code of Practice Published in July 2005, it provides local authorities with guidance on highways management in an ever changing environment, creating a strong foundation for a positive and lasting maintenance policy. Adoption of the recommendations in this code will help the delivery of Best Value services.
- The Manual of Contract Documents for Highway Works contains the primary documents required for the preparation of contracts for trunk road works. It consists of several parts, including the administrative procedures for its use, the specification for highway works and the corresponding method measurements.
- Interim Advice Notes (IANs) issued by Highways England contain specific guidance, which should only be used in connection with works on motorways and trunk roads in England, subject to any specific implementation instructions contained within an IAN. IANs are not part of the DMRB and the MCHW but must be read in conjunction. They may incorporate amendments or additions to documents in these manuals.
- Eurocodes - As a public body, Highways England expresses its requirements for the design and modification of existing structures (including geotechnical works) in terms of Eurocodes. Highways England’s technical experts were involved in the drafting of the Eurocodes and the National Annexes.
- The Network Management Manual (NMM) provides mandatory requirements, guidance and advice for the management of maintenance of the trunk road network.
- The performance requirements for routine and winter service activities on the trunk road network are included in the Routine and Winter Service Code.
- The Traffic Management and Maintenance Manual, published January 2013, sets out requirements for the management and maintenance of traffic technology systems.
Further information related to standards for highways is also available on the Standards for Highways online resource webpage.
ICE Training provides a range of courses to help you improve your understanding and knowledge of highways engineering. Courses include:
- Highway Design and Detailing using the DMRB
- Pavement Design Using the DMRB
- Specifying and using asphalts in roads and other paved areas with confidence
- Eurocodes courses