INTRODUCTION
• Firstly, a network is a facility consisting a set of nodes and
links. The urban road network plays a key role in the urban
spatial structure. Nigeria ranks top compared with other
countries in Sub-Saharan Africa in terms of road network.
The country has the largest road network in West Africa
with an estimated 200,000km of road network connecting
villages to cities. The Road transport assumed more
significant role and most utilized mode of freight
movement since the collapse of the rail system in the
1970s/80s. Today, road transportation accounts for nearly
95% of all modes of transport with estimated growth rate
of 10% per annum compared with other developed
countries such as South Africa, UK and US.

Cont.
It is possible to describe the road network in different ways. The
nine statements presented below can all be used to describe
the performance of the road network in terms of acessibility
(Rijin,2005).
1. A node has access to a network if a link exists between the
node and the network
2. The accessibility of a node with respect to a network is the
distance one has to travel to the nearest node on the next
hierarchy network
3. The accessibility of a node in a network is the total number
of direct connections with other nodes
4. The accessibility of a node in a network is the total number
of links connected to this network

Cont.
5. The accessibility of a node to another node is measured
as the travel cost between these nodes
6. The accessibility of a node in a network is the weighted
average travel cost between particular node and all nodes
in the network
7. The accessibility of a node in a network is the expected
value of the maximum utility of a visit to any node
8. The accessibility of a node in a network is (proportional
to) the spatial interaction between the node and all other
nodes
9. The accessibility of a node in a network is the total
number of people one can reach from a node with in
certain transport cost limit2.

DESIGN
• Designing successful transportation networks requires
more than the application of the functional
classification. In order to assist stakeholders in the
design process, a step-by-step design process is set up.
It is not a blueprint that tells stakeholders exactly what
to do, merely a framework within which they make
decisions. The stakeholders get to make the designs,
but the method brings structure to the design process,
by indicating which decisions need to be made and at
what point in the process. It is based on a number of
important characteristics, which are listed in random
order in Figure below.

CHARACTERISTICS
• A network can be defined as a set of linear
features through which resources flow. Nodes
(the end points of lines) are used as origins
and destinations, and links (lines) travers from
one node to the other. Nodes can have
properties but in network analysis we are
usually more concerned with the
characteristics of the links (Laurini and
Thompson, 1992).

HIERARCHY
• A road hierarchy has, for some time, been accepted as
one of the important tools used for road network and
land use planning. It is a means of defining each
roadway in terms of its function such that appropriate
objectives for that roadway can be set and appropriate
design criteria can be implemented. These objectives
and design criteria are aimed at achieving an efficient
road system whereby conflicts between the roadway
and the adjacent land use are minimised and the
appropriate level of interaction between the roadway
and land use is permitted. Basically, a road network is
classified into three, namely:

.
• ARTERIAL ROADs: These are also known as ‘Trunk A’. The
major function of this road is to provide mobility and it
further classified into the following:
– Free ways: This is a road network with a full access control
and has two or more lanes in each direction with exclusive
use of moving traffic and the access points at the
beginning and end of the road only.
– Express ways: This are more or less like a free way with a limited
access control and few number of access point
– Park ways: This are road network with full access control with no
access point. They are designed for journeys where delays of any kind
are not entertained, as such, the use of such facility attract some fees.

.
• COLLECTOR ROADs: These are also known as “Trunk B”. The
major function of this road is to collect traffic from local roads
and distribute it to arterial roads. Traffic using collector is
usually going to or coming from somewhere nearby. Unlike
arterials, collectors are designed to provide access to
residential properties. It further sub-divided into the
following:
– Streets
– Urban road

Cont.
LOCAL ROADs: These roads are also known as “Trunk B”. The
major function is to provide access. They characterized by
low speed limit, and carry low volumes traffic. In some
areas these roads may be unpaved. Local roads primarily
serve local traffic, provide connections within
communities, provide access to properties, and usually
have on-street parking. They further sub-divided into the
following:
-Feeder road
-Access roads

ASSESSMENT AND ANALYSIS
• In 2001, a process of risk rate mapping was
developed by TRRL for the European Road
Assessment Programme (EuroRAP) to enable the
risk of fatal and serious injury accidents occurring
on different parts of the British primary road
network to be compared (TRL 2005). As a second
stage of risk comparison, a risk rating system was
developed which ranked road sections according
to their road design features. This process initially
focussed heavily on the injury protection qualities
of the road design, and was described as a “road
protection score” (RPS).

CONTROL AND OPERATIONS
• Transportation had always played a vital role in the
development of any nation. This is borne out of the fact
that the primary function of transportation is to move
passengers or goods from a place of lesser value to a place
of higher value or utility. Transportation contributes two
types of utility: place and time utility, which in economic
terms simply means moving goods and people to where
and when they want. The effectiveness of road
transportation relies heavily on the type and condition of
vehicle under use, the road condition, the driver’s
competence, and the attribute of the driver to traffic
engineering, control, management as well as the policy
guidelines that give directions to the entire transport
system.

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