Connectivity and Accessibility

 

Introduction

Connectivity and accessibility – the use of two words immediately suggest that they are not the same thing. To illustrate this, take the example of three destinations, A, B and C, which are some kilometres apart – see the figures on the left.

 

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Figure 1

In figure 1, a transport link connects destination A with destination B. Destination C has no connections to anywhere.

 

Figure 2

Here, both A and C are connected to B, and by the same type of transport link. However, A is further away from B than is C. This which means that B is less accessible for A than it is for C.

Figure 3

In figure 3, someone who wanted to improve the accesssibility of C – and with money in his pocket – has built a high-quality (~ high speed) link between A and C, and also upgraded the link between A and B. This means that C is now directly connected to A; and with a bit of luck, someone travelling from C to B can now do so more quickly if he uses the high-quality links C-A and A-B. With figure 3, each of the three destinations is now accessible from the other two.

 

 Figure 4

In figure 4, the person living in C came up with an alternative set of improvements – a new  but normal transport link between A and C, and an improved, high-quality link between C and B.

In this figure, as in figure 3 each of the three destinations is connected to the other two. However it now takes less time to travel from C to B than it does from A to B –  in other words, seen from the viewpoint of B, C is more accessible than A. 

Things are more complex

The preceding notes talked about three destinations and about the transport links between them, but I did not say what type of transport link.

  • If they are all rail links, then even with the improved network of figure 4, for car drivers  there is no connectivity between any of the three destinations
  • If all the links are roads and the high-quality links are motorways, then in figure 3 cyclists from destination A have no connections to anywhere.
  • If B is an emergency medical centre, and there is a guideline time (such as “any point must be within 60 minutes ambulance drive from an emergency medical centre), then people living destination A may be alright with the connections in figure 3 but not with those in figure 4.
  • Suppose the transport links are bus routes, and higher fares are charged for high-quality links. If you live in destination C, then with the transport links shown in figure 4 a journey from C to B will cost you more. This means that you are connected by bus  to B, but its accessibility has gone down.
  • Suppose A is a regional centre. The improvements shown in figure 3 make it more accessible from B and C, strengthening A’s role in the structure of land uses.

In the real world

So we could say that, in the real world:

  • Transport links form networks. Change one link in the network and you change connectivity and accessibility throughout the whole network. Therefore any road study should begin with a network study.
  • Connectivity and accessibility are related to modes of transport. For example, building a motorway will not add new links for cyclists.
  • Connectivity and accessibility are affected by the cost of transport. As the cost of travel increases, accessibility decreases until the cost is so high that the trip is not made at all.
  • Changing connectivity and accessibility can weaken as well as strengthen an area’s land use structure.
  • Changing connectivity and accessibility may not be in line with social justice– building a motorway may improve accessibility for high-income earners (~car owners) but not for low-income earners.
  • Building new transport links is not always a “good thing”.

 

 

 

 

 

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About roadnotes

Robert Bartlett is an international consultant with over 30 years of professional experience as a highway and traffic engineer with leading companies and organisations in several countries, including Germany, China (Hong Kong), Qatar and the UK. Specialised in urban studies, transport and the use of GIS, research has included new ideas on subjects such as the study of social justice using GIS, the dimensions of vehicles, and comparative geometrics (highways and transport).
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