< Previous | Contents | Next >

PAN 57 Planning for Transport

ANNEX B: Personal Accessibility Analysis

B1. Personal accessibility can be affected by a number of factors including:

• An individual’s own mobility;
• By the physical disposition of destinations relative to the individual;
• By the availability of means of transport;
• Or by a combination of the three.

B2. There are 3 overlapping types of approach that can be used in accessibility analysis. All accessibility approaches relate to a specific location — an origin or a destination — and include zoning aspects and opportunity and deterrent features. All three approaches have a role to play in policy and project appraisal since different decisions require information to be presented in different ways.

B3. The choice of appraisal technique for any individual decision needs to be of an accuracy appropriate to the particular situation, with the resources devoted to the analysis being commensurate with the scale of the circumstances. Examples are given in Table 2 below. Analysis to support practical decision making will usually benefit from a more rigorous multi-criteria framework approach.

B4. Clear policies relating to a group of people for a particular purpose can be analysed in a straightforward manner. Accessibility analysis can though become complex and confusing if the question being asked is not identified at the outset. It is important therefore for all analyses to define problems clearly, gather the required supporting information and involve the relevant stakeholders. Consistent and rigorous techniques can assist in building consensus between various stakeholders.

Simple Approach:

B5. Isochrones are used to demonstrate the geographical distribution of impacts. This is the most commonly used approach internationally. It simplifies a given problem by defining thresholds. For the approach to be useful the choice of thresholds must accurately reflect some aspect of travel behaviour which is specific to local characteristics. This is because measures of accessibility have different values in different areas.

Recommended thresholds for local access:

(250m = walking threshold for public transport)

Recommended thresholds for regional / national access:

These are more difficult to define.

Values such as 15, 30 and 60 mins are useful.

Opportunity Approach:

B6. This sums all the available opportunities and takes into account a measure of deterrence related to how easily opportunities can be reached. Opportunity indices are relatively easy to interpret.

Value Approach:

B7. This measure considers the attractiveness of the available opportunities to represent their value as a transport choice in terms of time or cost. These indices measure efficiency but are less descriptive.

Zoning Aspect:

B8. This is a variable element. The level of detail is dependent on the policy / proposal being examined. Strategic issues will utilise wider geographical areas resulting in a more coarse zoning system. Larger zones provide a valuable overview of areas. Local issues will utilise more detailed localised representation. This will be much more time consuming and in some cases uneconomic.

Opportunity Features:

For example;

B9. Origin accessibility considers opportunities available to an individual or business. The opportunity is therefore based on the land uses at alternative destinations.

B10. Destination accessibility considers catchments for a destination. The opportunity is therefore based on land uses and types of traveller at alternative origins.

Deterrent Features:

For example;

- Time,

- Cost,

- Distance,

- The need to carry goods and/or other people.

B11. These are features that affect both the perceptions of travel and therefore influence real behavioural patterns. It is recommended that deterrence features of car available and non-car available trips is considered as many trips involve a number of modes and for non-car available trips the car options are excluded from the calculation.

Table 2. Types of Accessibility Analysis

B12. In considering the results of the accessibility analysis it should be remembered that the measures are intended to give only a general indication of levels of accessibility. They are though of assistance in identifying practical solutions and delivering schemes that will be of real benefit.

B13. Planning authorities should establish ‘accessibility profiles’ for sites taking into account the elements below. The profiles should reflect the catchment area served, likely quality of service and result in relative indicators of accessibility for different sites.

• Transport system accessibility by population sector to an opportunity:
  • A transport improvement or an increase in the number of opportunities will increase accessibility.
  • The scale of change is not easily assessed through qualitative comparisons.
• Accessibility to public transport services:
  • This is particularly useful if public transport services can be classified accurately in terms of their frequency or destination.
  • Obtaining detailed data on origins, destinations and routes of services can be a major exercise.
  • For accessibility of housing to public transport the recommended guidelines are less than 400m to bus services and over 800m to rail services.
  • Accessibility can be categorised, for example weak or strong.
• Accessibility to local facilities by walking and cycling:
  • A maximum threshold of 1600m for walking is broadly in line with observed travel behaviour.
  • If there is a significant population within 800m then improvements to the quality of walking and cycling networks will increase accessibility.
• Ratios comparing accessibility for different mobility groups:
  • One of the most useful measures is the ratio of accessibility for car available to non-car available people.
  • These ratios allow consistent comparisons to be made between locations.
• Accessibility for freight:
  • This is best undertaken using logistics management software.
  • It is usually undertaken at an individual company level.

< Previous | Contents | Next >