Key factors determining transport behaviour

The longest work journey is usually 30 minutes, Taltal13, CC BY-SA 3.0, via Wikimedia Commons

Travel behaviour is influenced by a range of interdependent factors. In this step, we’ll discuss the contribution of the ‘urban hardware’ on people’s everyday transport mode choice and activity patterns.

What is urban hardware?

This term describes urban and regional settlements and their movement infrastructures:

• how are cities and towns built (compact or spread-out, high or low density),
• which modes of transport and their networks dominate (fast or slow, public or private)?

We call these factors structural because they invariably change very gradually, even in cities or regions that pursue ambitious transformation agendas.

Urban hardware and time

Besides the visible aspects associated with the urban hardware, there is an invisible principle at work related to time. Over history, the longest one-way journey a transport user will make during a typical day (usually the journey to work or school) is approximately 30 minutes. This principle is known as the Marchetti constant after the researcher who popularised the concept in the 1990s.

So what does this mean for transport networks and settlement structures?

User behaviour and transport networks

User behaviour depends on the availability and utility of transport networks. In contemporary cities and regions, the networks for pedestrians, cyclists and private motor vehicles are generally ubiquitous enough to service all land uses.

Exceptions may apply to remote locations like small islands, or historic precincts and informal settlements where motor vehicles are excluded.

A practical form of exclusion (of non-motorised transport) is experienced in many urban areas built or rebuilt during the automobile age where dedicated pedestrian and cycling infrastructure is either lacking or poor and unsafe.

Beyond such constraints, a car user, cyclist or pedestrian can reasonably reach any destination after overcoming the factors of time and distance, and can do so at any time of the day, week or year.

For public transport networks a similar standard is usually only achieved in metropolitan centres and on key regional or intercity corridors. Elsewhere, the provision of trains and buses remains geographically and sometimes politically selective, and limits the amount and range of journeys users can undertake by public transport.

Urban DMA: density, mix, access

The proximity of travel destinations impact the choice of transport mode. Where places of activity are closely spaced and clustered, it is convenient to travel to, from and between them on foot, by bicycle or scooter. Where places of activity are scattered with longer distances in between, faster motorised modes are a logical choice.

Transport behaviour can thus be derived from:

• the density of settlements
• the mix of uses prevalent in them
• the access conditions they offer to different modes of transport.

This is known as the urban DMA: density, mix, access.

This last point touches on issues of urban and street design:

• is comfortable, barrier-free movement for pedestrians and cyclists catered for in the urban space?
• what about the integration of public transport stations and stops within the urban realm and with travel destinations?
• how fast and reliable (congested or not) is the road network, and what about the availability and cost of car parking at destinations?

Who travels?

Travel behaviour is structurally determined by who travels. Some demographic groups are more constrained than others, for example:

• people with mobility difficulties or disabilities face different challenges moving around than their able-bodied peers.
• people of higher socio-economic status exercise greater choice regarding the location of residence, workplace, and other regular destinations than those who are less privileged.
• socio-economic differences also manifest in rates of car ownership and the ability to travel for leisure purposes.