Travel time

On average, each person spends around 70 minutes per day on the move. This phenomenon, known as the “travel time budget” (TTB), has been extensively studied and found to be valid regardless of historical era, city, culture or means of transport.

In other words, all cities could be considered as being 70 minutes wide, and this has large implications for urban development. For example, cities structured around walking have a much smaller physical radius than cities structured around private or public transport.

In this article we will examine some of the findings and conclusions from the Urban Insight report “Running to stand still – the role of travel time in transport planning”.

 

How travel defines a city’s characteristics

While a city’s area coverage, density and population all change over time, its citizens’ travel time remains relatively constant. Research has suggested that humans are biologically programmed not to travel much more than an hour a day, and that this routine stretches back in time much longer than a century.

Economists might define this as a question of utility maximisation. The travel time budget would then express the time a person is willing to spend on travel in order to gain access to the supply of activities she or he desires. At a certain threshold, a point is reached where the increase in travel time does not pay off in terms of activities.

Another explanation points to the fact that travel is one of many activities that takes up time in people’s daily lives. A substantial amount of time is devoted to work, leisure, household chores and sleep, making it difficult or inconvenient for most people to allocate much more than 90 minutes for travel.

As a result, many cities have historically grown at the same rate as that enabled by increases in travel speed. An illustrative example is the way motorisation of European cities

during the mid-20th century (almost naturally) coincided with the dominance of Modernist urban development.

In recent years, the travel time budget appears to have increased slightly. This is not necessarily due to faster means of transport, but more likely because of increased travel comfort – including the possibility to combine travel with computer or phone use.

Regardless, travel stands out as one of the predominant behaviours affecting the size, characteristics and function of cities.

The travel time budget – a central factor in transport infrastructure strategies

The travel time budget and urban structures

The travel time budget teaches us that cities can follow quite different courses in their evolution and yet maintain a stable travel pattern. Historically, this has resulted in distinctly different urban structures offering roughly the same level of access. How do these structures differ, and what unites them?

In an idealistic comparison, we could look at three different cities, each with a transport infrastructure centred around a specific means of travel.

  • Walking: In a city with a dense core (0-2 km) dominated by walking trips, the potential level of access would be evenly distributed among the city’s ambulatory citizens.
  • Driving: A city centred around driving would be more dispersed and have a much larger radius (0-40 km). Its potential level of access would be high for those with cars but low for other groups.
  • Public transport: A public transport-oriented city would be dense and concentrated around station areas (0-20 km radius). The city’s potential level of access would decrease with the distance from stations.

Comparing these idealistic examples from the TTB perspective, the following can be stated:

If the travel time budget acts as a land use regulator, any increase in the average speed of the transport system leads to an (almost) equivalent decrease in population density and an increase in the dispersion of destinations. Thus, in terms of access, neither urban structure is more effective than the other.

Owing to the close relationship between travel and land use, a city exclusively based on walking can offer the same access in everyday life as a city based on automobile travel. While the walking-based city can offer equal access for anyone capable of moving around on foot, the automobile city offers an acceptable level of access merely for those guaranteed to travel with the high speeds offered by car.

A comparison of travel time use in cities in France, Belgium and Switzerland analysed factors that influence individuals’ travel time budget. The study found that access to cars and public transport infrastructure plays a minor role, while socio-economic and other factors (i.e., gender, age and presence of children in the household) had a greater influence on travel time budgets.

Put simply, the amount of time you spend on everyday travel is more a result of who you are than of the physical characteristics of your city or the modes of travel you use. Likewise, two cities can provide a different array of transport options and yet have the same distribution of travel time among their citizens.

For additional details, discussion and recommendations, read the full report “RUNNING TO STAND STILL – THE ROLE OF TRAVEL TIME IN TRANSPORT PLANNING”.

This Urban Insight report describes a phenomenon that is essentially a universal law of travel, with implications for both urban and transport planning. Its validity spans historical eras, as well as diverse cultures and cities. It touches upon what constitutes a limit for human behaviour and seems to affect the size and density of urban areas.

To the report

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