Movement And Access Functions On Urban Roads Environmental Sciences Essay
Roads are being constructed for the primary purpose of carrying people and goods according to O’Flaherty 2002. Over the years the demands of roads have also been for ever diversifying. As a result both the initial cost and the eventual lifetime cost are increasing. The management of roads an asset has also for this reason and more been regarded highly.
Likewise, for this purpose, roads are being classified to administrative, financial and legal reasons which are the crux of the management of the roads.
Classification has generally been done on the basis of an idealistic and theoretical hierarchical convention which has been questioned for reasons of use in new road construction and the like. In this piece of research this conventional model is being investigated based on a literature review. The classification practices and guidelines used in some developed countries were studied in to identify parameters that contribute to either function. An eventual fieldwork was done to find out what actually obtains in practice.
The objectives of the work are to identify suitable criterion for describing and measuring movement and access functions on urban roads. Identification of a relationship between these functions is also an objective.
To achieve these objectives, various parameters of the road that define these functions were first identified and prioritised. Based on the prioritised list, the collection of appropriate data like journey speeds, geometric data like roadwidth, number of lanes, sidewalks and the like were done from field survey.
The findings from the field survey would be outline in chapter six. Analysis of the finding would be made in the following chapter from which conclusions are drawn in the penultimate chapter.
Keywords: Movement, Access, Functions, Classification, Urban roads.
Chapter 1 Introduction
1.1 Background
As stated by O’Flaherty 2002, despite the fact that the purpose of road construction has been evolving since the early times, they are historically and fundamentally being constructed for the movement of goods and people. In the early times roads, were used for walking and riding using humans and various beasts to pull sledges, carts, carriages and the like and to carry goods. By the late nineteenth century, they were being used by cycles and motor vehicles such as cars, buses and lorries.
However, as the demands and desires of roads keep increasing and diversifying, they are being planned, designed, classified, constructed and maintained with different standards which depend on several factors. Today the location, to start with, of a new road will normally require the skills of planners, economists, geologists, surveyors, as well as road engineers (O’Flaherty 2002). It could also be influenced by politicians. Technical considerations will depend on the traffic volume, vehicle types, wheel loading, geometry, the performance expected of the road and the like. Classification of roads in a hierarchical manner does depend on all of these parameters but can be categorised into two functions:
Movement functions
Access functions.
This buttresses the assertion of Ogden et al (1996) that it is clear that there are several types of roads and streets but they can be grouped into two distinct functional groups.
1.2 Problem statement
Movement and Access functions have been used to classify roads based on the conventional relationship as shown in the figure 1.1 below. This is theoretical and idealistic. Full movement functions would mean roads carrying high volume of traffic and speed with no local traffic. Complete access function roads or streets on the other hand would mean total unrestricted access with local traffic. However this project will endeavour to investigate these based on a literature review and a field study by collating appropriate data to find out what the graph would look like in practice. Even though there can be two functional classifications it is still clear that despite the class within which a road is categorized, it would still be serving a proportion of both functions.
Figure 1.1 The conventional road hierarchy
Source: (Ogden et al, 1996)
1.3 Project purpose
The overarching purpose of the project is to satisfy the requirements for the award of a Master of Science degree (MSc) and of an even greater importance, is to classify roads with mixed functional characteristics, more aptly and thereby precisely allocating legal and administrative responsibilities and improving the management efficiency of roads in general.
1.4 Aims and Objectives
1.4.1 Aim of the project
The aim of the project is to investigate the interrelationship between movement and access functions on urban roads in order to provide methods of describing and quantifying these functions. This will be based on a thorough literature review of appropriate and available materials. The findings would then be tested in a real life case study from which conclusions would be made.
1.4.2 Objectives of the project
The main objectives of this project are as follows:
To establish a suitable criteria for describing movement functions on urban roads
To establish suitable criteria for measuring movement functions on urban roads
To establish suitable criteria for describing access functions on urban roads
To establish suitable criteria for measuring access functions on urban roads
To establish relationships between the movement and access functions
1.5 Scope of the project
The project will therefore attempt to first of all establish suitable criteria for describing and measuring both the movement and access functions on urban roads. A relationship will be developed between the two based on an extensive literature review. These would then be applied to a case study in order to verify the relationship between them. A road typically serving a mixture of both functions will be used.
The scope of the project will be limited to the following:
Identification of Movement and Access parameters based on a literature review of journals, textbooks, and other published and the internet.
Prioritisation based on the significance of the effects of these parameters to either function.
Selection of data requirements from prioritised list.
Collection of data for each parameter from field survey or create or generate data from available data sources.
Analyse findings from the field survey data.
Compare the relationship if any between theory and practice.
These will be constrained by the availability of time, relevant literature, human resources, equipment availability and other forms of logistics.
1.6 Thesis structure
The contents of this thesis which comprises of eight chapters are summarised in the subsequent paragraphs.
Chapter 1 gives an introduction of the topic. It states the purpose, aims, objectives and scope of the research project and gives the structure of the thesis.
Chapter 2 details the methodology for the development of this research project with the help of an appropriate flow chart
Chapter 3 details the literature review that was undertaken for the project. It gives a brief description of the history and development of roads. The types of roads and the significance of road classification are outlined together with the rationale and guidelines used for classification in some countries.
Chapter 4 outlines the parameters that could be used to define describe and quantify both movement and access functions. These parameters are subsequently prioritized based on the ideal scenario.
Chapter 5 outlines the process of data collection. This starts with the identification and description of the area of study and the methods, equipment and procedure used.
Chapter 6 presents the collated and refined findings from the field survey and other sources. The results are presented in a logical and rational manner to enhance optimum understanding from the data to augment the analysis.
Chapter 7 analyses and discusses the findings of the field survey. The discussions include a brief background of the road network in Sierra Leone and the system of classification in existence and ways of improving them based on the findings of the research project.
Chapter 8 presents the conclusions from the research project, which was based on the information as presented in the preceding chapters. It also presents recommendations based on the findings.
Chapter 2 Methodology
2.1 Introduction
This chapter describes the approach that was used in the execution of the research project activities that have culminated into this thesis. It gives the systematic sequence of the activities and to some extent signifies the logic of the adopted method.
The method is based on six activities, so group together to respond most profoundly to the aims and objectives of the project. This notwithstanding adequate and relevant consideration was given to pragmatism and availability of resource (human support resource), logistics, timeframe or duration and relevant literature.
The methodology followed six steps as shown in the flow chart in figure 2.1below.
Figure 2.1 Methodology flow chart
2.2 Review of Literature
Fundamental to most, if not all researches is a thorough knowledge base. Consequently, this research was in no way an exception to this. A literature survey and review was undertaken of published journals, text books, which were relatively scarce, and lots of other materials from the internet. The review was geared towards garnering a solid knowledge base that would boost the analysis, field work and decision making as the research project progressed. A key focus of the review also was to identify the research line and to identify suitable criteria to describe and measure movement and access functions on urban roads. The effects of the various parameters on the classification of road were also investigated in order to establish a prioritised ranking.
2.3 Identification of description and quantification criteria
Diverse parameters, to varying extents could be used to describe and define movement and access functions. A long list of parameters that could ideally be used to classify roads based on the level of service they provide, within a network was established. From this, a priority list that was eventually used for the field survey was developed. As the effects of each parameter vary, they were ranked according to their significance as contributors towards each of the functional characteristics and according to the conventional hierarchical functional classification. The data eventually collected from the field survey were based on this ranking and governed by the other limitations of time, human resource and accessible logistics.
2.4 Study Area and field survey
A study area was selected having decided upon the required parameters. that would have to be collected. Ideally movement and access functions could better be investigated for a combination of various types of roads including primary roads, secondary roads, local streets and the like and could be executed within a whole catchment area to get actual performance and characteristics of the various parameters over time and on different road types. However, due to the limitations of time, scope and logistics, a road stretch with a mixture of both movement and access functions and varying other relevant characteristics was chosen. The A38, Bristol road running from Lee Bank Middleway circle at the intersection with the A4540 at the city centre to Ashill road, Rubery about 14Km was selected. A detailed description of the study area is given subsequently in chapter 5.
2.5 Analysis of Data
The data collected from the field were then collated and transformed into informative graphs and other statistical outputs. These were then used to analyse the findings in a bid towards identifying pertinent relationships between the two functions.
2.6 Discussions
A discussion of the findings was then done to express understanding of the findings and how they relate to existing literature as well as practices used in different parts of the selected regions of the world. This discussion also includes relating findings to Sierra Leone.
2.7 Conclusions and recommendations
Based on the findings in practice, knowledge acquired from existing literature and the entire activities of this individual research project, conclusions and recommendations were then made in the penultimate chapter before referencing.
Chapter 3 Literature Review
3.1 Introduction
In this chapter a detailed review of existing literature was done to garner adequate information in order to be in good stead to justify the need of the project. The gap between existing knowledge of theory and what obtains in practice was identified based on practices in four countries.
3.2 Historical overview on road development
Various literatures in relatively recent times including O’Flaherty 2002, records that the actual birth of roads had been lost amidst ancient history but it is without doubt that the trails purposely selected by early man and his pack animals were the harbingers of today’s roads. With civilization and increased desire for communication trails gradually developed into pathways which in turn evolved into recognized travelways. Most of these ridgeways, as they were otherwise called, were located on hillsides where bushes were less dense and walking much easier. Wheel invention (in Mesopotamia in ca 5000BC) and the development of an axle which joined two wheels, made it possible to carry with relative ease, heavy loads. This necessitated the provision of wider travelways with firmer surfacing having the capability of carrying concentrated loads but with less steep connecting routes down to or up from valleys and fordable streams ( O’Flaherty, 2002). Examples of early manufactured roads included stone paved streets of Ur in the Middle East, the corduroy-log paths near Glustenbury, England (ca 3300 BC) and brick paving in India. Despite these examples the Romans are credited for being the premier professional road-makers.
3.2.1 Roman roads
The Roman road system, at its peak consisted of 29 major roads from Rome to the outskirts of the empire and totalled about 78,000 km. The roads were constructed wide enough, commonly around 4.25 metres, to ensure the ease of passage of two chariots and six legions marching abreast. Most of the time gradients were reduced by cutting tunnels and the roads were more often than not, characterised by straight sections on embankments 1 metre to 2 metres high. This helped to keep the carriageway dry. The Romans also built some 5,000 km of roads in Britain radiating from the capital London and extending to Wales and Scotland during its occupation in 55 BC according to O’Flaherty 2002. Despite the Roman roads being the fundamental highways for communications internally, over a very long period of time they eventually decay and disintegrate due to weather, traffic and human inventiveness.
3.2.2 United Kingdom roads
The words road and street became popular during the sixteenth and seventeenth century particularly in England. ‘Road’ is believed to have possibly come from the verb to ride meaning a route along which one can progress by riding and from the Latin word ‘ via strata” meaning a paved road. http://en.wikipedia.org/wiki/Street.
The highway act 1555 in Britain required local parishes to maintain their roads. Turnpike Trusts were therefore established in 1706 as a result of the variable and mostly poor state of the road.
By the 18th Century, trade became more important and the manufacturing industries in Great Britain steadily developed.
After 1750’s the development of the toll significantly contributed towards the development of roads in that:
It promoted the development of road making techniques in Britain by allowing the emergence of skilled road makers like Telford and John Loudon Mc Adam.
It established the notion that road users should pay some road costs
It determined the framework for the 20th century’s pre-motorway trunk road network
The commencement of operations of the steam powered railway service symbolised the beginning of the end for Turnpike trusts as majority of long-distance travel almost spontaneously moved from road to rail once towns became accessible by the railways.
With the abolition of the trusts, roads reverted to their original system of parish maintenance. Many independent road boards then emerged (15 000 in England and Wales alone). The situation became chaotic and in 1882, Parliament decided and agreed to accept the financial responsibility for aiding construction and maintenance.
During the first forty years of the twentieth century, evolutionary developments occurred, emphasizing on layout and dust control by using tar and bituminous surfacing and reconstructing existing roads. Organized road research directly applicable to the UK conditions was initiated in the 1930’s with the establishment of small experimental stations at Harmondsworth Middlesex where research was carried out into highway engineering, soil mechanics and bituminous and concrete technology; this was the start of Transport Research Laboratory (TRL).
The development of a strategic inter-urban trunk road network of over 15000km (including the construction of some 3100km of new motorway and over 3500km of dual carriageway) was also the stimulant for the initiation of the major pavement technology and traffic management research programmes in particular, the Transport Research Laboratory.
3.2.3 United States of America contribution
The passing of the Federal Highway act of 1944 in USA authorizing the development of interstates and defence highway system to connect 90 per cent of American cities having population in excess of 50 000, by means of about 70 000 km of motorway culminated in a giant leap in road technology.
Significant research programmes, including the development of special tests tracks for pavement material study, design and construction were initiated as a consequence of this decision. The outcomes of these research programmes and the development of associated road making and traffic management techniques were turned to be of major influence to road development in the international scene. (O’Flaherty, 2002)
3.3 Functional classification concept
The process by which roads and streets are grouped into classes, or systems reflecting the character of service they are intended to provide is referred to as functional classification. http://www.fhwa.dot.gov/planning/fcsec2_1.htm . Fundamental to this process, is the recognition and acknowledgement that roads and streets individually, do not serve travel independently in any major way. As a matter of fact, most travel would involve movement through a network of roads and therefore the determination of how this travel could be channelled logically and efficiently within the network becomes vital. This however can be done by defining the part any particular road or street plays in serving the flow of trips through the highway network. The nature of this channelization process would normally be defined by the functional classification.
This idea is illustrated in the schematic shown in figure 3.1.
A: Desire lines of travel
B: Road network provided
Figure 3.1 Channelization of trips
Source: Federal Highway Administration guidelines section II-I
For simplicity, the relative width of lines represents the comparative amounts of travel desire with straight lines connecting trip origins and destinations. The relative sizes of circles represent the relative trip production and attraction powers of the places shown. Figure 3.2 B shows trips being channelized on a limited road network in a logical and efficient manner as it is impractical to provide direct line connections for each and every desire line. The terms local, collector and arterial describes the functional relationships of the facilities in the diagram. However this hierarchy relates directly to the hierarchy of travel distances which they serve.
Cities and larger towns normally generate and attract a larger proportion of the relatively longer trips. The arterial highways generally provide service for such travel. The collectors which are the intermediate functional category serve small towns directly and connect them to the arterial network and collects traffic from the bottom level system of local roads which serves individual farms and other rural land use. Figure 3.2 below shows a functionally classified rural road network.
Figure 3.2 Illustration of a rural highway functionally classified network
Source: Federal Highway Administration guidelines section II-I
In urban areas additional considerations, like spacing, is vital in defining a logical and efficient network.The same rudimentary concepts apply for urban like for rural roads. Similar hierarchy of systems could be defined. This notwithstanding, the rather high landuse intensity and travel throughout and within an urban area results in difficulty ti identify centres of travel generation. Figure 3.3 shows a schematic of a functionally classified urban street network. http://www.fhwa.dot.gov/planning/fcsec2_1.htm. In addition to traffic channelization, is the dual role of providing access and travel mobility played by the highway network. Access is a necessary requirement at the start and end of any trip whilst mobility can be provided at varying levels along trip paths. This is sometimes referred to as ‘level of service’ which encompasses a vast range of elements including riding comfort, speed change freedom and the like but the most important being operating speed or travel time.
.
Figure 3.3 Schematic illustration of a portion of an urban street network
Source: Federal Highway Administration guidelines section II-I
The concept of traffic channelization leads logically not only to a functional hierarchy of systems but also to a parallel hierarchy of relative distance served by those systems. This hierarchy of travel distances can be associated logically with the functional specialization in meeting the access and mobility requirements. Local facilities emphasize land use functions whilst Arteries emphasize a high level of mobility through movement. Collector however compromises in-between these functions. Figure 3.4 illustrates this.
Locals
Collectors
Arterials
Land use
Mobility
Figure 3.4 Relationship between traffic mobility and land use on functionally classified systems.
Source: Federal Highway Administration guidelines section II-I
3.4 Road systems
Road systems are developed fundamentally to group roads of similar functional characteristics into distinct systems. Two road systems albeit exists. These, as stated by Gichaga and Parker (1998) are:
Urban Road System
Rural Road System
However the Federation Highway Association (FHWA) functional highway classification system in United States of America (USA) further subdivides the urban area systems into two, namely:
Urbanised area systems
Small Urban area systems
Small urban areas were defined as those places, as designated by the Bureau of Census having a population of five thousand (5000) or more and not within any urbanized area. (FHWA Guideline Section II-I)
Urban and rural areas are characterised differently in terms of human and vehicular population density, types of land use, nature of travel patterns, street and highway networks density, and the interrelationship of all these elements and their effect on the definition of the highway function. As a consequence, rural and urban roads are normally classified differently. FHWA Guidelines Section II-I)
3.4.1 Urban roads system
Urban roads systems are structured in a manner to enhance road safety. They basically include the following classes of roads:
Primary distributors which are normally constructed to high standards and forms the primary network
District distributors which distributes traffic to and within central business districts in large urban areas, large residential areas and industrial areas
Local distributors which distribute traffic within an environmental area
Access roads which provides direct access to buildings and plots in a given environmental area. Gichaga and Parker (1998)
3.4.2 Rural roads system
Rural roads essentially form a critical link within a road transport network by facilitating access and promoting development of rural areas. A major portion of most road networks is made up of rural roads and they normally carry low volume traffic. This system includes the following classes of roads
Primary or trunk roads which are constructed to a high geometric standard and including motorways or expressways or freeways
Secondary roads which provides access to most parts of a nation
Feeder roads, which generally connects development areas to secondary or trunk roads
Access roads radiating from feeder roads. (Bjorn Johannessen 2008)
3.5 Classification of roads
Based on the functional characteristics roads are also further generally categorized within a functional system as follows:
Arterials
Collectors
Local / Side streets
3.5.1 Arterials
Arterial roads are moderate or high-capacity roads which provide a level of service immediately below that of a highway. They provide a high level of service at great speeds for the longest uninterrupted distance of travel and with some degree of access control. Normally arterial road carry large volumes of traffic between areas in urban centres. They have intersections with collectors and local streets and are designed to carry traffic between communities or neighbourhoods but do lack direct residential entrances. Arterial roads also serve as a link between expressways and freeways with intersections. Shopping centres, supermarkets, gas stations and other forms of business often line these roadways.
Depending on the local access intersections, pedestrians and the extent of development the speed limit vary between 50 to 100km/h. Arterial roads are formed either from a planned suburban layout and purposely built or they may otherwise result from the upgrading of main rural roads when countryside is transformed into residential use. The geometry of arterial roads also vary and can be up to five lanes in width in mid-sized communities but could be up to 8 lanes in large cities and in such circumstances they may serve dual duties as local and as state highways. Examples of arterials include East Lancashire road in northwest England and Eastern Arterial road in New South Wales, Sydney Australia.
Traffic flow on arterial roads usually go through large signalized intersections with other arterials and/or traffic circles, many collector roads and smaller intersections which have stop signs only on the smaller road. Other entries to the road, if any, would be for major commercial (or perhaps industrial) uses, designed for traffic, a large residential complex and the like. http://en.wikipedia.org/wiki/Arterial_road.
3.5.2 Collectors
Collector roads are low or moderate-capacity roads which are below a highway of arterial functional class. Collectors provide a comparatively lesser mobility service compared to arterials. They tend to lead traffic from local roads or sections of communities or neighborhoods to areas of activities within communities, arterial roads or even directly to motorways, expressways or freeways. Collectors may have varying characteristics. Some are wide boulevards entering communities or connecting sections. In residential areas, some may occur as residential streets typically wider than local roads but with only a few wider than 4 lanes. These occur mostly in extremely dense areas.
Like arterials, collectors may be lined with commercial amenities but to a far lesser extent whilst schools, churches, recreational facilities can be commonly found on residential collector roads.
Collectors are formed based on planned activity and are purposely built. Occasionally however, in a grid system they fill the gaps between arterial roads.
The speed limits on collector roads range between 30 km and 60 km in built-up areas depending on the extent of development, local access frequency, intersection and pedestrians as well as the surrounding area. In older areas, traffic calming mechanisms are also occasionally used on collector roads.
Examples of collector roads include the following:
The major A452 around Chelmsley wood and Castle Bromwich in Birmingham with M6 motorway on the outer side of the curve.
The much more minor ‘Grahame Park Way’ around the Grahame Park estate (and next to the RAF Museum) in Colindale, north London, with the Midland Main Line and the M1 motorway on the outside. http://en.wikipedia.org/wiki/Collector_road.
3.5.3 Local streets
These are last in the hierarchy of the roads and normally would distribute traffic within local communities. They would also provide access to farm lands in agricultural areas. These at times could be really minor and therefore not categorised with a road number. Local streets are generally minor highways leading mostly off a main road or a major street in a residential area in the case of an urban road system. They are generally of little significance to through traffic, being the last kilometres or miles of travel. Common characteristics of local streets include low speed limits typically not more than 50km/h, kerbside parking and few or no paint markings displaying lanes. Intersections in urban and suburban areas are usually with stop signs or in some suburban areas where intersecting with similar streets yield signs are installed. In rural areas, some intersections are not controlled. Local roads would normally represent the largest components in most public road networks in terms of total length.
Occasionally, a place of worship or a school may be located on local street, but they are mostly lined with residences. In a residential areas however, it is quite uncommon to find any commercial development.
Local streets when built are basically intended for the traffic only of residents and their visitors. However, many local streets that do not have a dead end are also used by motorists in congested areas.
3.6 Purpose and need for classification
The overarching aim of classification of roads into a hierarchy based on functionality is to subdivide them into identifiable groups, classes or types which will reflect the predominant role of the roads that make up the network for the following reasons:
Administration and financial responsibility
Planning, design, operations and maintenance. (Ogden K W and Taylor S Y 1996)
The objectives of the classification are to enhance management when used to guide planning, design and operations of a road network by:
Reducing delay and/or congestion along the roads and networks
Maintaining the traffic carrying capacity and consequently delaying costly capacity improvements as far as possible
Improving general road safety and reducing car crashes
Assessing the degree of frontage access control to be exerted along a road
Deciding on the extent of constraint that can be exerted on traffic to improve the amenities of a road
Improving movement to and from businesses, shops supermarket, schools, hospitals and the like
Identifying areas of further improvement for creation of acceleration and or decelaration and climbing lanes
Coordinating land use decisions
Improving the general aesthetics appeal of road corridors.
3.7 Practical road hierarchy
There is an obvious need for the continuous evaluation of the functional classification system on a regular basis and at a relatively frequently to ensure accurate reflection of the traffic function of a particular route at the present time and for the foreseeable future. http://www.fhwa.dot.gov/environment/flex/ch03.htm. This goal is fundamental but different systems are employed by different institutions and nations to achieve this goal.
Functional classification is done on the basis of a conventional hierarchy with movement being associated with through traffic mostly in the arterials and access being associated with the local roads or side streets. This leaves a large gap in between that should cater for what is usually observed in urban areas especially, where there is a mixture of both movement and access functions on most roads. The conventional road hierarchy though dealing with the functional efficiency of traffic flow is also concerned about safety and other amenities as well as environmental qualities of urban areas. Non-traffic concerns in the context of urban areas are taken into consideration although in doing so, traffic issues are considered first and other issues fitted around them ( Marshall, 2005) .
Major roads therefore tend to be associated with heavier traffic volumes, strategic routes, high design standards and limited access to minor roads with frontage access. Minor roads on the other hand, tend to be associated with lesser traffic volumes, lower design standards, local routes, frequent access points and with residential accesses.
Consequent upon these associations are the following:
most routes tend to be designated based on the transport and traffic function,
there tend to be great segregation between transport modes at the extremes of this hierarchy with segregated vehicular traffic at one end and segregated pedestrian traffic at the other and the all purpose roads in between.(Marshall, 2005)
The appropriateness of the conventional hierarchy model has however been questioned for the following reasons as stated by Ogden et al (1996) quoting Brindle (1983):
The concept of the ‘hierarchy of development’ based on functional community and coherent facility catchment which is fundamental and an integral part of the model according to Ogden et al (1996) again quoting Russell (1968) is itself both by observation and in theory challenged
A wide range of intermediate roads between major traffic routes and minor streets with conflict of movement and access functions and this leads to lower levels of safety and amenity than desirable.
It is tedious to apply to existing networks for traffic management and other purposes
Even with the designing new communities or suburbs, the hierarchical relationship between roads cannot always be sustained. Therefore the ensuing disputes over the appropriateness of designation can sometimes lead to inappropriate design standards.
Functional classification is used to categorise roadways according to their predominant role in the highway network and also on the basis of their physical setting.
3.8 The classification of roads in some regions in the world
3.8.1 Australia
The Victorian code (VicCode) for residential development offers the following guidelines for classification in Australia as shown in table 2.1.
Table 3.1 VicCode, Victoria Australia
Functional Classification
Description, Functions and Characteristics
Major Arterials
Routes which form the basis of inter-urban networks( including freeways) and providing a high level of service for users.
Infrequent access
Most access would be grade separated, roundabouts, signal based and these would typically be other traffic routes or trunk collectors
Arterials
Typically forms the main grid of traffic routes.
Often forms long continuous routes and highly connective.
Caters for the bulk of urban travel.
They would be suitable for moderate levels of trunk travel
Functional Classification
Description, Functions and Characteristics
Sub-arterials
Routes which typically serve to provide finer traffic routes more than other categories – typically connecting to less than four other traffic routes before a significant connectivity change.
They would have frequent access connection to local streets. The percentage of trucks on this road would be low but would form the basis for local routes for buses
Trunk Collectors
Provides specialized form of connection between traffic route system and residential streets where it is desirable to channel local traffic to an outlet while at the same time not attracting through traffic.
The primary function is to enhance convenient and safe movement of residential traffic to and from major arterial system usually at signalized intersections.
They are not residential streets but residential development may be considered on these streets with site planning condition which ensure acceptable amenity and which provide for vehicle entrance and exits in the forward direction
Collector Streets
Collects traffic from access places and access streets and could carry a higher volume of traffic.
A reasonable level of residential amenity could be maintained by restricting vehicle speeds and traffic volumes.
Speed should be controlled by street alignment and intersection designs.
Access Streets
Residential environment dominates and traffic is extremely subservient.
Low speed and traffic volume and pedestrian and bicycle movement are enhanced.
Vehicle speed is controlled by street length or alignment.
Preferably access should serve no more than 100 dwellings.
Access Lane
Principally provides access to side or rear lot for parking of vehicles
In very low speed environment and between 3m to 8m in width
Source: Department of Planning and Housing 1992 (Ogden K W and Taylor S Y 1996)
3.8.2 Germany
In Germany six levels of mobility are recognised. These range from level 1 which is the highest level of vehicular traffic to level 4 the lowest level of mobility. The physical settings also influence classification and uses guidelines that distinguish between a large number of roadway settings. The first criterion is rather similar to AASHTO’s rural and urban distinction, but considers whether or not the road is outside or within a built-up area.
The second criterion considers the physical aspect of the setting that is whether or not the road is framed by buildings. The final criterion considers non-vehicular uses of the roadway that is whether or not the roadway is used largely for vehicular or pedestrian access or whether or not it serves the role as a public gathering place. This is one of the most important distinctions from the AASHTO approach, since it contains the implicit understanding that roadways serve many functions beyond that of simply carrying vehicular traffic.
Roadway categories in the German Gridline are shown in table 2.2 below
Table 3.2 Roadway categories in the German Guidelines
Level of Mobility
Functional Category
Outside built-up areas
Within built-up areas
Not surrounded by buildings
Surrounded by buildings
Mobility
Access
Public Realm
A
B
C
D
E
I
A I
B I
C I
II
A II
B II
C II
D II
III
A III
B III
C III
D III
E III
IV
A IV
B IV
C IV
D IV
E IV
V
A V
–
–
D V
E V
VI
A VI
–
–
–
E VI
Source: Street Design and Community Livability
A simplified example for the assessment of roadway usage in the German functional classification with description and characteristics is shown in table 2.3.
Table 3.3 Simplified grid of roadway assessment
Predominant Function
M: Mobility
Importance
Explanation
A: Access
P: Public Realm
Very high
High
Intermediate
Low
Very low
Mobility
M
Local road
Automobile Travel
M
Cul-de-sac, no through traffic
Parking
A
No driveways
Transit
M/A
No transit
Bicycle Travel
M/A
Unfavorable topography
Pedestrians
A
Commercial Establishments
Pedestrian Crossing
A/P
Commercial establishments
Social Activity
P
Important recreational destination
Children Play
P
A lot of playing activity observed
Other special usage (e.g. Greenery)
Important recreational destination
Evaluation:
This roadway is an important public realm because of the recreational significance of the surroundings
Predominant Function: Public Realm
Roadway Classification: Local
Source: Streets Design and Community Livability
3.8.3 United Kingdom (UK)
The classification guidelines used in the UK is shown in the table 2.3 below.
Table 3.4 United Kingdom hierarchical classification of roads
Functional Category
Functions
Description and characteristics
Primary Distributors
Predominant activity
Fast moving long distance traffic with no pedestrian and frontage access
Pedestrian Movement
None. Segregation between vehicles and pedestrians
Stationary vehicles
None
Heavy Goods Vehicle (HGV) activity
Suitable for HGV movements especially through trips
Vehicle access to individual properties
Only from sites of national traffic importance
Local Traffic Movements
Extremely few- junction spacing preclude local movement
Through Traffic Movements
Predominant role for long distance
Vehicle operating speeds and speed limits
More than 65 km/h depending on geometric constraint
District Distributors
Predominant activity
Medium distance traffic to primary network
Public transport services
All through traffic with respect to environmental areas
Pedestrian Movement
Minimum pedestrian activity with a positive measures for pedestrian safety
Stationary vehicles
Some depending on traffic flow conditions
Heavy Goods Vehicle activity
Minimum through trips
Vehicle access to individual properties
None apart from major centres, i.e. equivalent to local distributor level of vehicle flow
Local Traffic Movements
Some- only a few localities may be severed, junction spacing important
Through Traffic Movements
Predominant role for medium distance traffic
Vehicle operating speeds and speed limits
Subject to approximately 50 to 65 km/h limits within built-up area
Local Distributors
Predominant activity
Vehicle movements close to the beginning and ends of all journeys
Bus stops
Pedestrian Movement
Controlled with channelized crossings (e.g. zebra)
Stationary vehicles
Considerable if off highway facilities are not provided
Heavy Goods Vehicle activity
Minimum through trips
Vehicle access to individual properties
Some- close to more significant activity centre
Local Traffic Movements
Predominant activity
Through Traffic Movements
None
Vehicle operating speeds and speed limits
Subject to approximately 50 km/h limit but layout should discourage speed within built-up area
Access Roads
Predominant activity
Walking, Vehicle access, Delivery of goods and servicing of premises, Slow vehicle movement
Pedestrian Movement
Considerable freedom allowing random crossing
Stationary vehicles
Some but depending on safety considerations
Heavy Goods Vehicle activity
Residential: related activities only
Other area: delivery of goods and services
Vehicle access to individual properties
Predominant activity
Local Traffic Movements
None
Through Traffic Movements
None
Vehicle operating speeds and speed limits
Less than 30km/h with devices that control speed
Pedestrian Streets
Predominant activity
Walking, Meeting, Trading
Pedestrian Movement
Complete freedom and this is the predominant activity
Stationary vehicles
None except for servicing and emergency
Heavy Goods Vehicle activity
Essential servicing and frontage delivery only
Vehicle access to individual properties
None (except for emergency vehicles and may include limited access for servicing)
Local Traffic Movements
None (but may include public transport)
Through Traffic Movements
None
Vehicle operating speeds and speed limits
Less than 8km/h (vehicles enter on sufferance)
Source: Institute of Highways and Transportation (1987)
3.8.4 United States of America (USA)
In USA functional classification is based on the American Association of State Highway and Transportation Officials (AASHTO) guidelines which differentiate between three levels. These are arterials, collectors and local roadways. Arterials serve corridor movements with long lengths of trips and high volumes. The physical setting is also taken in to consideration in USA by the systems classification. Under AASHTO based system the roadway setting is simply defined as urban or rural with a distinction made based on area wide population density. This means that the system adopted classifies roadways over a fairly wide geographical area. AASHTO method is therefore distinguished by it simplicity. Therefore there are the urban area systems, the small urban area system and the rural system. (Garrick and Kuhnimhof, 2000) The classification is shown in table 2.5 below.
Table 3.5 AASHTO System of Highway classification
Level of Mobility
Roadway Setting
Rural
Urban
Mobility
Principal Arterial
Principal Arterial
Minor Arterial
Minor Arterial
Collector
Major Collector
Minor Collector
Access
Local
Local
The classification is also shown pictorially in figure 3.5 as an organisational chart based on hierarchy.