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Do You Know That? Zahavi’s Conjecture and Household Transport Budgets

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Electric Vehicles and Mobility

École des Ponts ParisTech

4.5 (218 notes) | 5.2K étudiants inscrits

The purpose of Electric Vehicles and Mobility is to help you, whatever your profile, your training or your country, find your own answers to questions such as: - Will electric vehicles be the last to be allowed in megalopolises in the 21st century? - Does the environmental gain from vehicle electrification justify heavy investment in charging infrastructure? - Are electric vehicles only for wealthy people in developed countries? This course will allow you to acquire elements from engineering science, sociology, environmental science, political science, economics, management science, in order to evaluate, analyze and implement the diffusion of electric vehicles where their use is relevant. This MOOC is the English version of Mobilités et véhicules électriques; in the lecture videos, the teachers speak in French, nevertheless their presentation is in English and English subtitles are available. Groupe Renault and ParisTech schools have been working together for almost 15 years on topics related to sustainable mobility. Together, they created two Master programs (Transport and Sustainable Development in 2004, Mobility and Electric Vehicles in 2010) and the Sustainable Mobility Institute Renault-ParisTech in 2009, to support ongoing changes. Electric Vehicles and Mobility is the result of this shared history and was developed from a course delivered within the Master Mobility and Electric Vehicles, led by Arts et Métiers ParisTech in partnership with Ensta ParisTech, Mines ParisTech and École des Ponts ParisTech.

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À partir de la leçon

Chapter 1 - Understand Mobility and its evolutions

</p><p>In this first chapter we will focus on mobility, we will characterize it according to urban forms and lifestyles. Then, we will study more specifically electric mobility and its evolution over time, which will allow us to analyze the changes induced by the electric vehicle on the mobility system.</p><p>In this chapter, each “class” (video <em>Lecture</em>) is preceded by a video <em>More on method</em> that defines a tool or concept used in the lecture and is followed by a video <em>Do you know that?</em> which widens the horizon of the course or enlights it from a particular angle.</p><p>Finally, you will be able to test your understanding in the following section devoted to the assessment of the week in a graded quiz (some single-answer questions, some multiple-answer questions). This evaluation concerns only the videos <em>Lecture</em> and is required to obtain the certificate.</p>

More on Method - Mobility Systems Observational Data2:58

Electric Mobility: From Past to Present13:17

Do You Know That? National Wealth and Individual Motorization2:58

More on Method - The Four-Step Model3:06

Electric Mobility: Actual Changes Brought On by Electric Vehicles in Terms of Mobility Systems11:29

Do You Know That? Zahavi’s Conjecture and Household Transport Budgets4:42

Enseigné par

Émeric FORTIN
Head of the Master in Transport and Sustainable Development
Virginie BOUTUEIL
Researcher

Transcription

The rise of cars in the 20th century allowed for much faster travel in many cities,

especially in developed countries.

One could expect this increase in speed to be a time-saver,

which would give households more work or free time.

Studies directed in the 1970s by Jacob Zahavi disproved that theory.

By analyzing travel time budgets in several cities over the world,

Jacob Zahavi observed that households took advantage of the faster speeds

not to reduce their travel time, but to go further and access more opportunities.

This idea was formalized as Zahavi's conjecture.

It states that cities are characterized by a constant travel time budget over time

of around 1 hour.

Several studies have backed up this conjecture in many other cities over

the world.

For instance, let us consider the Paris region.

In 2001, the average time spent in transport was relatively stable and around 1 hour and

10 minutes,

whatever the area of residence, from Paris to the most remote areas

and whatever the motorization level of the household.

Zahavi's conjecture must be understood as an average behavior

observed for a sufficient number of individuals like a law of large numbers.

At an individual level, travel time budgets vary widely depending

on the individual's age, economic activity, etc.

The increase in speed does not lead to time saving but to an increase

in traveled distances.

Let us look at Paris region again.

In dense areas, traffic congestion, low speeds, and traveled

distances remain moderate.

But as we move further away from the center of the agglomeration, congestion

decreases, speed increases, which leads to longer distances

traveled per day.

Why the increase in distance?

Households take advantage of the speed to move further away and enjoy

cheaper real estate or gain easier than before access

to new opportunities, shopping centers, places to go out, etc.

This leads us to the second conjecture of Zahavi which states

that a household's average transport monetary budget, is also

stable over time and around 15% of the city in question's

average income.

When cities develop economically, they use cars more often.

An increase in income leads to an increase in transportation costs, which

keeps the transportation burden around 15%.

Although it was corroborated by other studies, the second Zahavi conjecture

is not as solid as the first one.

It must be understood from a global standpoint, in other words,

at the metropolitan level.

Within a metropolis, the increase in traveled distances

leads to a strong increase in transport burdens as we get

further away from the center.

In Paris region, the average burden ranges from 8% for Paris inhabitants to 21% for households

living the furthest away, in rural areas.

The motorization rate also plays an important part as cars are more

expensive than public transportation, as Zahavi noted.

As a conclusion, the first Zahavi's conjecture is

sometimes called "Zahavi's curse".

Introducing more efficient transports leads to an increase in traveled distances

and thus, to an increase in environmental nuisances, especially

greenhouse gases.

To avoid this race for more and more speed, some researchers

advocate returning to slow cities, to allow

for more sustainable mobility.

This solution would be less expensive than another solution involving

massive investments in greener technologies which would reduce

emissions per kilometer traveled and offset the effects

of distance but could be very expensive.

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