15. Traffic Management
15.1 The Aim of Traffic Management
Traffic management can be thought of as the application
of a defined traffic control policy to an area or an extended length of
road, with the aim of achieving a specified set of community objectives.
This means that traffic management is distinguishable from a traffic control
action which applies to a particular intersection or troublespot.
The types of objectives which may be required for
a particular traffic management scheme include:
- improvement of traffic conditions e.g. reduction
of congestion;
- improvement of physical environment e.g. reduction
in noise pollution;
- improvement of access e.g. to commercial areas;
- improvement of safety e.g. slowing of vehicles
to improve pedestrian or child safety; and
- reduction of parking problems.
In some cases a traffic management scheme will be
proposed in response to a particular problem or set of problems, and the
measures to be used will be fairly obvious. In other cases the nature of
the problem/s may be more complex and a range of alternative traffic management
schemes must be devised and assessed. Implementation of a traffic management
scheme will usually mean an alteration in traffic flow patterns. This in
turn will mean that some roads, or sections of road, will carry heavier volumes
than previously, while other sections will carry lesser volumes. The community
will therefore probably perceive that some members of the community are advantaged,
while others are disadvantaged with the introduction of the scheme. Trade-offs
may therefore have to be made between different benefits and disbenefits.
This trade-off often occurs within a trial implementation of the scheme.
In recent years the term Traffic Calming has been
widely used, both in the technical literature and in the popular press,
to refer to a particular thrust of traffic management. Objectives of traffic
calming usually include:
- reduction of vehicle speeds;
- creation of conditions which encourage drivers
to drive calmly;
- removal of extraneous traffic;
- enhancement of the environment; and
- improvement of road safety.
15.2 Traffic Management Principles
The most important principle in traffic management
comes from recognition of the fact that each of the objectives of any traffic
management scheme is influenced by the volume, composition and speed of
the traffic which occurs in the network. With this in mind, the design principle
may be stated in bland terms as ‘decide where the traffic is to go, and where
it is not to go, and apply measures to achieve the desired traffic distribution
and flow characteristics’.
In order to implement this principle a defined road
hierarchy is required. This hierarchy is established so as to produce categories
of roads and streets which can be linked to their functional purpose and appropriate
traffic levels.
Each road in a system has a balance of traffic and
access functions. These two functions have an inverse relationship: if a road
has a higher traffic function, then it has a lower access function, and vice-versa.
The particular point of balance between the functions is used to classify
roads into different levels of the hierarchy. Because the traffic and access
functions are seen as being continuous, the road classes are not clearly
defined but merge from one to the other. Most functional road classification
systems currently used in Australia reflect these characteristics. The measures
applied to achieve desired traffic levels in traffic management often comprise
combinations of actions to reduce volumes on some links and actions to increase
volumes on other links. Actions to reduce volumes may be absolute (e.g. street
closure) or may be less stringent discouragement actions (e.g. pavement narrowing).
Actions of the latter type are usually aimed at increasing either the capacity
or speed of traffic on roads designated to carry major flows (e.g. introduction
of clearways).
15.3 Functional Classification of Roads and Streets
The purpose of road classification is to provide
a common basis for establishing policy. While these policies may cover a
range of administrative, design or operational matters, the fundamental classification
from the viewpoint of traffic network planning and design is a functional
classification, i.e. a classification according to the traffic carrying purpose
of the road.
A functional classification system might identify
the following road categories:
- Access Roads – being culs de sac not more than
200 metres in length and other minor roads intended to be used for access
to residential buildings.
- Collector Roads – being roads intended primarily
to provide access to residential buildings and to access roads.
- Distributor Roads – being roads intended primarily
to provide access to residential buildings and to collector roads, and to
connect neighbourhoods to sub arterial roads. These would also normally carry
public transport.
- Sub Arterial Roads – being roads intended primarily
to provide access to distributor roads and to carry through traffic. Access
to residential properties would not normally be permitted.
- Industrial Roads – being roads intended primarily
to provide access to land developed or intended to be developed for industrial
purposes.
- Arterial Roads – being roads intended primarily
only to carry through traffic. Access to residential property would not be
permitted.
Although the traffic function of streets and roads
is well understood, their (social) function as social and community spaces
is not. The principal social function is to provide public space for social
contact of various kinds, and therefore the primary design objective should
be to discourage through traffic from local roads.
The design width, grade, alignment and construction
of a street or road should enable a driver to immediately recognise the
class and function of the road. Thus when a driver is confronted with a narrow
winding road they are forced to lower their speed, or take a different route.
The driver can then drive their vehicle accordingly. This is one of the reasons
that winding roads have become popular in the last few years. Another reason
is that curved streets look much better as the streetscape is constantly changing.
The road names, such as Court, Crescent and Drive also indicate the class
of road.
15.4 Traffic Management Strategies
The road classification plan provides a framework
for the development of traffic management strategies which address the specific
issues associated with particular roads and streets.
A procedure for the development of a strategy for
a road network is:
(a) Define the area of the network for which a traffic
management strategy is to be developed.
(b) Conduct a survey of the study area, including
traffic volumes, travel times, traffic problem locations, identification
of different interest groups, views of interest groups, etc.
(c) Identify the desired objectives of the traffic
management scheme, together with measures of their achievement.
(d) Develop alternative proposals to achieve the
desired objectives.
(e) Carry out initial assessment of the various
proposals, including prediction of changed traffic flows, impacts on all
relevant groups, and general performance of each scheme relative to the stated
objectives.
(f) Select the preferred scheme and undertake
more detailed design and analysis.
(g) Implement the scheme on a trial basis, monitoring
feedback and modifying the scheme as appropriate.
(h) When satisfactory operation of the scheme
occurs, complete final implementation.
This procedure will need to be carried out with appropriate
input and feedback from all interested stakeholders. If this does not occur
it is likely that any final proposal will not receive community support.
15.5 Major Urban Road Networks
Traffic management schemes will seek to make travel
on the major road system (arterials and sub-arterials) as attractive as
possible so as to encourage their use. Measures to achieve this may include
the following:
- Parking Bans. Parking bans, including the introduction
of clearways during peak hours, provide additional traffic lanes without
the need for construction work. Such bans may of course provide a disbenefit
to adjacent landholders.
- Access Control and Reduction. The performance
of arterial roads is greatly improved if the arterial traffic has absolute
priority at intersections with minor streets. This can be achieved by the
use of Stop or Give Way signs. However, even if this absolute priority exists
significant interference may still occur, and consideration may be given to
limiting the number of intersections at which access to the arterial is possible.
- Intersection Improvements. The critical points
on most arterial roads are the intersections. Hence there is potential for
intersection improvements to greatly influence the performance of the road.
- Coordination of Traffic Signals. Coordination
of traffic signals along an arterial road or throughout a road network can
have the effect of increasing the overall capacity of the network without
reconstruction of the individual intersections.
- Designation of Heavy Vehicle Routes The removal
of heavy vehicles with large dimensions and slow acceleration characteristics
to particular routes may allow the rest of the network to perform more efficiently.
15.6 Residential Areas
The preparation of traffic management schemes for
local residential areas must be undertaken in the context of overall traffic
management. Actions taken on arterial roads will have significant impact
on local roads and vice versa. A local traffic area is an area bounded by
arterial roads in which through traffic is of limited importance, and can
therefore be justifiably restrained.
Modern subdivision design will usually attempt to
‘design in’ Local Traffic Areas and so encourage through traffic to use the
arterial road system. Older established areas may be able to encourage the
development of local traffic areas by the following types of treatments on
local streets:
- Reduction of intersection conflicts by the use
of Stop or Give Way signs.
- Reduction of statutory speeds.
- Reduction of local street connectivity by full
or partial intersection closure.
- Reduction of local street connectivity by partial
prevention of access from major roads.
- Discouragement of through traffic by reducing
width of intersection openings from major roads.
- Reduction of speeds by changes of road format.
- Discouragement of through traffic by change of
nature of street entrance.
- Reduction of intersection speeds by use of roundabouts.
- Reduction of speeds by physical speed control
devices e.g. bumps, humps, dips, rumble strips, etc.
- Prohibition of large vehicles.
15.7 Rural Roads
The objectives of traffic management for rural roads
can be broadly classified as:
- capacity (e.g. increasing capacity at slow points
by the use of auxiliary lanes);
- safety (e.g. reinforcing a driver's perception
of safety by the use of consistent signing of hazards); and
- quality-of-service (e.g. providing motorists
with sufficient rest areas).
Page last modified 3 July 2003.