A New Metric with Which to Address Transport Inequality

A New Metric with Which to Address Transport Inequality


Tom Cohen, UCL Centre for Transport Studies


Index of personal travel impact (IPTI) is introduced as an alternative to accessibility measures. Its derivation using income-adjusted cost, travel time and crow-flies distance is described, and its use in addressing transport inequality explored.


Accessibility measures, though well-intentioned, are cumbersome because they have to reflect the full range of destinations that can be reached from a given location. They tend to lack a financial component which is a crucial failing given that poor connectivity is closely associated with low income. Furthermore, when they are used to inform policy decisions, it is necessary to make paternalistic decisions concerning which journeys “matter” most. This is both invidious and prone to error.
An alternative metric, “index of personal travel impact” (IPTI), has been developed in response to these weaknesses. At the individual level, it reflects the journeys which a person would like to be able to make (as opposed to the destinations available to them), therefore circumventing the need to make assumptions about their travel preferences. By adjusting absolute cost to reflect individual wealth, it represents the real financial impact of travel. By combining this with door-to-door journey time, it brings together into a single unit the two most significant impacts of travel – time and money. And, by deriving a rate per unit distance using the straight-line path between origin and destination, it also captures the often more circuitous journeys that a sparse public transport network imposes upon those who lack access to private motorised transport.
This metric can be used to support policy tackling inequality as follows: first, a citizens’ assembly is convened to deliberate concerning what should be the maximum level of IPTI. Government (central and/or local) then becomes responsible for bringing all who live in its jurisdiction within the chosen threshold. In some cases, there will be clusters of people whose IPTI exceeds the threshold. This may result from the poor quality or high cost of links to a major trip attractor. Appropriate policy responses may be to improve those links so that they become quicker and/or to subsidise them to reduce their financial impact. In other cases, those with high IPTI will be scattered, reflecting more their personal circumstances (low income or reliance on poor public transport, say) than point-based weaknesses of the transport network. Here, individual financial support or the provision of a vehicle or taxi service for certain journeys may be the most appropriate responses.
The index of personal travel impact (IPTI) is a pragmatic way of addressing transport inequality. And, by promoting targeted action, it will ensure that large-scale intervention (such as a new public transport service) is only employed where this represents a more efficient mechanism than assisting people individually.


Association for European Transport