Sustainable Mobility: A Review of Possible Actions
and Policies
Mariano Gallo * and Mario Marinelli
Department of Engineering, University of Sannio, 82100 Benevento, Italy; [email protected]
* Correspondence: [email protected]; Tel.: +39-(0)8-2430-5565
Received: 28 June 2020; Accepted: 9 September 2020; Published: 11 September 2020
Abstract: In this paper, a review of the main actions and policies that can be implemented to
promote sustainable mobility is proposed. The work aims to provide a broad, albeit necessarily not
exhaustive, analysis of the main studies and research that from different points of view have focused
on sustainable mobility. The structure of the paper enables the reader to easily identify the topics
covered and the studies related to them, so as to guide him/her to the related in-depth studies.
In the first part of the paper, there is a preliminary analysis of the concept of sustainable mobility,
the main transport policies implemented by the European Union and the USA, and the main statistical
data useful to analyze the problem. Next, the main policies that can promote sustainable mobility
are examined, classifying them into three topics: Environmental, socio-economic, and technological.
Many of the policies and actions examined could be classified into more than one of the three
categories used; for each of them, there is a description and the main literature work on which
the topic can be analyzed in more detail. The paper concludes with a discussion on the results obtained
and the prospects for research.
Keywords: sustainable mobility; transportation; review
1. Introduction
The concept of sustainable mobility derives from the broader concept of “sustainable development”,
defined as the “development that meets the needs of the present without compromising the ability of future
generations to meet their own needs” [1]. The term “sustainable mobility” was coined five years later [2];
the following overall objective is associated to sustainable transport: “To ensure that our transport
systems meet society’s economic, social and environmental needs whilst minimising their undesirable impacts on
the economy, society and the environment” [3]. All the main definitions found in the literature stress that it
is not enough to refer to environmental aspects, although they are of primary importance, but also
social and economic impacts must be taken into account. Moreover, strategies to pursue the objective
of sustainable mobility cannot be limited to producing/using less polluting transport systems, although
this is of fundamental importance.
Promoting sustainable mobility is one of the most widespread objectives in transport policy, at all
territorial levels, whatever the “political color” of the decision-maker. Nowadays, no plan, project,
or policy direction concerning the transport sector does not (at least) mention the concept of sustainable
mobility. From a scientific standpoint, the international literature has been and continues to be massively
interested in the subject, from multiple points of view (technological, territorial, urban, social, economic,
health, etc.). For example, to date (3 April 2020), the words “sustainable mobility” or “sustainable
transport” in a generic web search are quoted about 4.23 million times and are contained in over
60,000 publications indexed on Google scholar, and over 18,500 publications indexed on Scopus.
Many other references can be found in languages other than English.
Sustainability 2020, 12, 7499; doi:10.3390/su12187499
Sustainability 2020, 12, 7499 2 of 39
A survey report on this argument is, therefore, a difficult challenge and, necessarily, will not cover
all possible facets of the problem or be exhaustive. In this paper, the state of the art on sustainable
mobility will be covered from three main angles: Environmental, socio-economic, and technological.
1.1. Related Works
In the literature, several reviews can be found on sustainable mobility or some of its single topics;
limiting to some of the most recent ones only, here we refer to [4–18]. In [4], the effects of technology
on promoting the shift in behavior towards sustainable transportation modes are investigated.
Gonzales Aregall et al. [5] reviewed green port strategies for reducing negative externalities on
hinterlands. The innovative strategies for last-mile logistics were reviewed in [6]; another review on
sustainable logistics is proposed in [17]. Taiebat et al. [7] reviewed the implications of connected
and automated vehicles on sustainable mobility; the prospects of autonomous driving were studied
also in [12]. Reviews on shared mobility were proposed in [8] and [10]. Electric mobility was examined
in [9] and [11]. Technological innovations in transit systems and their impact on environmental
and social sustainability are studied in [13]. More general reviews on sustainable mobility can be
found in [14–16,18].
This paper tries to give an overall description of the subject and the individual topics, focusing on
the importance of the contribution that each topic can give in the near future to sustainable mobility.
1.2. Methodology
The review was based on the following classic steps: (a) Choice of sources; (b) keyword search;
(c) screening and selection of papers; (d) in-depth analysis of the main topics covered.
The sources used were: (a.1) Scopus, Science Direct, and MDPI site, for scientific papers; (a.2) Google
for technical and transport policy reports, and some proceedings; (a.3) specific sites for some topics or
data (World Health Organisation, Environmental European Agency, European Commission, Eurostat,
Environmental Protection Agency, etc.).
The keyword search was addressed to (b.1) general keywords (“sustainable mobility”, “sustainable
transport”, “transport and environment”, “sustainability”, etc.); (b.2) specific keywords for each
topic (“air pollution”, “car-sharing”, “noise”, “ecodriving”, etc.), combined with “transport”,
“transportation”, “traffic”, and “mobility”. Moreover, other papers were identified by examining
the references of more recent papers.
The papers found with this keyword search were very numerous. A careful analysis and selection
phase was necessary, knowing that an exhaustive review would not be possible. The selection criteria
were based on (not in order of importance): (c.1) Diffusion and prestige of the place of publication;
(c.2) type of product, favoring journal papers over conference proceedings; (c.3) centrality of the paper
with reference to the topic in which it is cited; (c.4) date of publication, favoring the most recent ones,
all other characteristics being equal; (c.5) diffusion in the scientific community based on citations.
Finally, for each topic, further research was carried out by examining other work mentioned in
the papers selected in the previous phase.
1.3. Structure of the Paper
Many topics related to sustainable mobility can be classified in more than one of the 3 categories
listed above. For example, electric cars can be classified both from a technological and environmental
point of view. In Table 1, the main topics we will discuss in this paper are presented by theme. The circle
indicates the theme in which the topic is covered, while × indicates another point of view in which
the topic can be classified.
The main purpose of this paper is to provide the reader, after a brief analysis of the problem,
with an overview of the main policies and actions that can promote sustainable mobility. The references
reported also allow those who want to deepen a single topic to have a solid basis for specific research.
Sustainability 2020, 12, 7499 3 of 39
Finally, the paper can be useful to policymakers as it provides a compendium of actions that can be
implemented or included in wider transport policy programs.
Table 1. Topic classification.
TopicTheme Environmental Socio-Economic Technological
air pollution • × ×
car-sharing × •
connected and automated vehicles × × •
cycling promotion • × ×
ecodriving • ×
electric and hybrid vehicles × •
equity •
e-commerce × •
fuel × •
green-house gases • ×
intelligent transportation systems × •
micro-mobility × •
noise • × ×
pricing × •
public transport promotion × • ×
safety • ×
taxes and incentives × •
teleworking × •
traffic-lights × •
transit improvements × •
walking promotion • ×
This paper is organized as follows. Section 2 examines the main transport policies and statistical
data on sustainable mobility. Sections 3–5 examine environmental, socio-economic, and technological
topics, respectively. Section 6 discusses the results and Section 7 concludes.
2. Transport Policies and Statistical Data
2.1. Transport Policies
European transport policy has always focused on the sustainability aspects of transport. The White
Paper on Transport [19] outlines the transport policy for 2050. European transport policy aims at a 60%
reduction in greenhouse gas emissions by 2050, with the following 10 targets:
1. “Halve the use of ‘conventionally fuelled’ cars in urban transport by 2030; phase them out in cities by
2050; […].
2. Low-carbon sustainable fuels in aviation to reach 40% by 2050; also by 2050 reduce EU CO2 emissions
from maritime bunker fuels by 40% (if feasible 50%).
3. Thirty per cent of road freight over 300 km should shift to other modes such as rail or waterborne transport
by 2030, and more than 50% by 2050, […].
4. By 2050, complete a European high-speed rail network. Triple the length of the existing high-speed rail
network by 2030 and maintain a dense railway network in all Member States. […]
5. A fully functional and EU-wide multimodal TEN-T ‘core network’ by 2030, with a high-quality and capacity
network by 2050 and a corresponding set of information services.
6. By 2050, connect all core network airports to the rail network, preferably high-speed; ensure that all core
seaports are sufficiently connected to the rail freight and, where possible, inland waterway system.
7. Deployment of the modernised air traffic management infrastructure (SESAR) in Europe by 2020
and completion of the European common aviation area. […].
8. By 2020, establish the framework for a European multimodal transport information, management
and payment system.
Sustainability 2020, 12, 7499 4 of 39
9. By 2050, move close to zero fatalities in road transport. In line with this goal, the EU aims at halving road
casualties by 2020. […].
10. Move towards full application of ‘user pays’ and ‘polluter pays’ principles and private sector engagement
to eliminate distortions, including harmful subsidies, generate revenues and ensure financing for future
transport investments.” [19].
Some of these goals are very ambitious. For example, the former calls for the complete elimination
of the use of conventional fuel cars in urban areas by 2050 and their halving by 2030. It can be seen that
most of the objectives listed (from 1 to 6), which should, therefore, guide European transport policy
over the next 30 years, tend to promote and develop sustainable mobility, with a strong emphasis on
rail transport for passengers and goods and reducing the use of transport systems and fuels that have
a strong environmental and climate-changing impact. Goal 9 focuses on another important aspect of
sustainable mobility: Transport safety. Goals 7 and 8 promote investments in technologies, while goal
10 tries to introduce more equity by charging more for the use of infrastructure and the production of
pollution, also to gather resources to finance investments in the transport sector.
A more recent document [20] addresses the issue of sustainability in Europe until 2030, including
mobility issues. About mobility, this paper refers to the Action plan for low-emission mobility [21]
that states “Low-emission mobility is an essential component of the broader shift to the low-carbon, circular
economy needed for Europe to stay competitive and be able to cater to the mobility needs of people and goods”.
This document confirms the main goals provided in the White Paper and identifies the following pillars
of the action plan, underlining the centrality of sustainable mobility in the European transport policy:
• Optimizing the transport system and improving its efficiency (ITS, pricing, multi-modality);
• Scaling up the use of low-emission alternative energy sources (low-emission alternative energy
for transport, standardization, and inter-operability for electro-mobility);
• Moving towards zero-emission vehicles (vehicle efficiency, action on heavy-duty vehicles);
• Horizontal enablers to support low emissions mobility.
For urban areas, in the Action Plan on Urban Mobility [22], the European Commission proposed
20 actions; among these, eight refer directly to sustainable mobility on the following topics: Sustainable
urban mobility plans; sustainable urban mobility and regional policy; transport and health in urban
areas; campaigns on sustainable mobility; energy-efficient driving; lower and zero-emission vehicles;
clean and energy-efficient vehicles; internalization of external costs.
Particular attention is paid to the SUMP (Sustainable Urban Mobility Plan) that is defined as
follows: “A Sustainable Urban Mobility Plan is a strategic plan designed to satisfy the mobility needs of people
and businesses in cities and their surroundings for a better quality of life. It builds on existing planning practices
and takes due consideration of integration, participation, and evaluation principles.” [23]. This planning tool
is becoming increasingly popular, although it is not mandatory; today [24], over 1100 cities in Europe
have prepared a SUMP.
Sustainable mobility is promoted, albeit in a less organic way, in the USA, where there is an
overlap of powers and competences between the federal state and the individual states of the union,
as underlined by [25] that proposed a review of policies between 2000 and 2011. The same paper shows
how “[…] there is a lack of governmental mandates for sustainability actions […], and there are (rightly so) more
local sustainability initiatives and programs than federal ones […]”.
It is well known that many cities in the United States have been built and developed as car-oriented
systems. Only recently, some cities (e.g., Boston, Dallas, Houston, Los Angeles, Minneapolis, Pittsburgh
and Seattle) are trying to promote more sustainable transport alternatives by redesigning their roads
to accommodate cyclists and buses and introducing Light Metro (LRT) and Bus Rapid Transit (BRT)
lines [26].
This analysis leads to identifying how the European transport policy is focused on sustainable
mobility, with particular reference to reducing emissions. Furthermore, there is a strong trend towards
the elimination or extreme reduction in the use of conventional fuels for passenger and freight transport,
Sustainability 2020, 12, 7499 5 of 39
favoring electric mobility for land transport: Rail transport, in urban and suburban areas, and electric
or zero-emission vehicles, in urban areas. This trend, in addition to having an important impact
on future mobility habits, is expected to direct the automotive industry to invest more and more in
alternative fuel vehicles, with particular attention to electric vehicles. This industrial transformation is
already beginning to be seen today, with an increasing presence of electric or hybrid car models and a
corresponding growth in market share.
2.2. Main Statistical Data
There are many statistical sources useful to study sustainable mobility at the global level and its
impacts; most of the data refer to aspects related to air pollution and greenhouse gas emissions, although
studies and data on road accidents, congestion, and noise can be found. The main government agencies
that collect, analyze, and publish data on environmental issues are the Environmental European
Agency (EEA) [27], the U.S. Environmental Protection Agency (EPA) [28], the U.S. Department of
Transportation (DoT) [29], and the World Health Organization (WHO) [30].
The amount of data available is very large and is, of course, updated on an annual basis. In this
section, only some data are reported to highlight the significant impact of transport on environmental
sustainability aspects.
The Environmental European Agency [31] estimated the total pollutant emissions in Europe
(EU-28) and the percentage of the same emissions from the transport sector. Focusing on particulate
emissions, which are the most harmful to human health, it can be seen that the transport sector is
responsible for about 13%, of which about 11% due to road transport. Transport sector emits, instead,
about 47% of NOx (39% due to road transport). The same agency [32] estimates greenhouse gas
emissions in Europe; the transport sector produces 946,902 kt CO2 eq., equal to 21.9% of the total.
In the USA (at the year 2016), transport sector produced about 29.3% of total greenhouse
gas (GHG) emissions [33]; the Environmental Protection Agency [34] estimated 387 kt of primary
PM10 from transport (17.1% of all classified sources), of which about 65% due to road transport.
Data on consumption and emissions are distributed by Energy Information Administration (EIA) [35],
while transportation noise data can be found in the National Transportation Noise Map [36].
At the global level, the World Health Organization publishes, inter alia, data on the effects of air
pollution on human health [37] and road accidents [38]. Air pollution is the biggest environmental risk
to health in the world, killing 3 million people each year. Road accidents, instead, cause 1.35 million
deaths and up to 50 million injuries worldwide.
Many other data useful for the analysis of sustainable mobility can be found in other statistical
sources. In Europe, Eurostat [39] provides data on transport safety (all modes), greenhouse gas
and pollutant emissions, energy consumption, and more generally on transport systems and their use.
3. Sustainable Mobility: Environmental Topics
This section examines the main sustainable mobility issues related to environmental aspects of
the problem.
Sustainable mobility policies are very focused on environmental protection; sometimes, sustainable
mobility is identified only as mobility that is able to reduce environmental impacts. Even if this concept
is not correct, indeed most of the interventions aimed at the development of sustainable mobility
have as their main objective the reduction of pollutant emissions and greenhouse gases. In fact,
in the following sections of the paper, although dedicated to other topics, it will be noted that many of
the socio-economic and technological aspects of the problem also have environmental objectives to
achieve (see Table 1).
As shown in Table 1, the following topics will be referred to in this section: Air pollution; cycling
promotion; eco-driving; green-house gases; noise; and walking promotion.
Sustainability 2020, 12, 7499 6 of 39
In more detail, air pollution and greenhouse gases are treated only in general terms because
the possible actions on transport for their reduction are numerous and are specifically dealt with in
the other parts of the paper.
This section is organized as follows. Section 3.1 describes the problems related to air pollution
and global warming caused by transport, with the corresponding social, economic, and human
health impacts, and the main approaches to their reduction, which are dealt with elsewhere in
the paper, are identified. Section 3.2 examines the main actions to promote “soft mobility”, i.e., cycling
and pedestrian modes of transport. Section 3.3 looks at eco-drive techniques for energy saving, both on
road and rail transport systems. Finally, Section 3.4 studies the problem of noise pollution and possible
mitigation and reduction measures.
3.1. Air Pollution and Greenhouse Gases
In summary, air pollution is defined as any alteration of the natural characteristics of the Earth’s
atmosphere. We refer, talking about mobility, to anthropogenic causes. It is well known that there can
also be natural causes of air pollution and that mobility contributes only partially to all man-made
pollution. Greenhouse gases, on the other hand, are not real pollutants, as carbon dioxide is naturally
present in the atmosphere. The high concentration of CO2, produced by anthropogenic causes,
is responsible of global warming and climate change.
Another fundamental difference between air pollution and greenhouse gases is that the former can
be more or less harmful depending on where the pollutants are emitted; in fact, the main damage of air
pollution is to human health and depends on the number of people exposed. In particular, air pollution
is a major and serious problem in large urban centers, where there is also a high concentration of
population. On the other hand, greenhouse gases have a global effect on the climate, regardless of
where they are emitted and whether or not people are exposed.
The main pollutants produced by transport are [31]: PM10 and PM2.5 (particulate matter),
O3 (ozone), NO2 (nitrogen dioxide), BaP (benzo[a]pyrene), SO2 (sulphur dioxide), CO (carbon
monoxide), and benzene. In Table 2, the percentages of the urban population in EU-28 exposed to
concentrations above certain reference value are reported. The corresponding impacts on human
health are significant (see Table 3).
Table 2. Percentage of the urban population in EU-28 exposed to air pollution (2015–2017) [31].
Pollutant EU Reference Value
Urban Population
Exposure [%]
Quality Guidelines
Exposure Estimate [%]
PM10 Day (50 µg/m3) 13–19 Year (20 µg/m3) 42–52
PM2.5 Year (25 µg/m3) 6–8 Year (10 µg/m3) 74–81
O3 8 h (120 µg/m3) 12–29 8 h (100 µg/m3) 95–98
NO2 Year (40 µg/m3) 7–8 Year (40 µg/m3) 7–8
BaP Year (1 ng/m3) 17–20 Year (0.12 ng/m3) 83–90
SO2 Day (125 µg/m3) <1 Day (20 µg/m3) 21–31 Table 3. Premature deaths attributable to exposure to main air (2016) [31]. Pollutant Premature Deaths in Europe Premature Deaths in EU28 PM2.5 412,000 374,000 NO2 71,000 68,000 O3 15,100 14,000 The main greenhouse gases emitted by transport systems are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Greenhouse gas emissions are usually measured in CO2 eq., where 1 t of CH4 equals 21 t of CO2 eq. and 1 t of N2O equals 310 t of CO2 eq. Total greenhouse gas emissions worldwide amounted to 37.9 Gt CO2 in 2018 [40]. The variation between 1990 and 2018, for the different sectors, is summarized in Table 4. It can be seen that in Sustainability 2020, 12, 7499 7 of 39 EU28, only the transport sector has increased. On a global level, however, the increase affected all sectors. This analysis shows that even in the countries of the European Union, where policies to reduce greenhouse gas emissions have been pursued, the transport sector is the only one with a significant increase, while in all other sectors, emissions have decreased. It, therefore, shows that we are still a long way from a solution to the greenhouse gas reductions generated by the transport sector. Table 4. Changes in CO2 emissions from 1990 to 2018 by sector [40]. Sector Globe EU28 Power industry +82% −30% Other industrial combustion +60% −40% Buildings +6% −34% Transport +77% +21% Other sectors +110% −20% The high concentration of greenhouse gases is now considered by almost all scientists to be the cause of climate change, which could prove disastrous in the coming years. The research aimed at estimating the damage caused by climate change is so numerous that it would need to receive a specific review. Here, referring to some work, in which you can find further references, we quote [41–49]. In particular, a welfare theoretic approach to estimate the damage caused by climate change is proposed in [41], while the consequences on economic growth are examined in [42]; an economic quantification of damage is reported in [45,48]. Legal aspects related to climate change damage are examined in [43], while a human rights-based approach is reported in [46]. Specific studies are reported in [44,49] for the US and in [47] for China. The transport policies proposed to reduce pollutant and greenhouse gas emissions are numerous and many of them are covered in other sections of this article. Indeed, most of the actions reported in Table 1 have as a direct or, more rarely, indirect effect a reduction in pollutant and greenhouse gas emissions. These policies may be classified according to the subject on which they act: • The vehicle: Low-emission vehicles, electric vehicles, hybrid vehicles, etc.; • The fuel: Low-carbon fuels, biodiesel, etc.; • The users: Use of less polluting modes of transport, changes in mobility habits, incentives, pricing, etc.; • Management technologies: Intelligent Transportation Systems (ITS), traffic control, connected vehicles, etc. This analysis shows that emissions are one of the main external impacts of the transport sector, causing serious damage both on the planet and on the human health of the people exposed. Most policies promoting sustainable mobility put the reduction of emissions at the heart of their actions, as also highlighted in Section 2.1. It is believed that the objective of reducing emissions will remain primary for a long time to come, at least until zero-emission vehicles are widely deployed. At present, the problem is particularly acute in developing countries, both because of the rapidly growing need for mobility and because it is economically impossible for large sections of the population to access new, low-emission vehicles. Therefore, it would be useful to envisage appropriate economic support policies in these contexts, to promote the transition to clean vehicles, in addition to the actions that are usually planned in more developed countries. 3.2. Cycling and Walking Promotion The promotion of walking and cycling, also known as “soft mobility”, is one of the most popular sustainable mobility policies in urban areas. The propensity to use these modes of transport is linked to the urban environment, which should be redesigned overall [50–52]. Increased use of non-motorized modes, especially when replacing motorized trips, has several positive effects. The effects on the environment are, of course, only if the trip made by bike or on foot is Sustainability 2020, 12, 7499 8 of 39 a substitute for a trip otherwise done by car. Clearly, this type of trip has a distance limit. Usually, pedestrian trips can replace car trips within a range of up to 1–2 km, while bike trips can be up to 10 km. For example, in Italy, a survey by ISFORT (an Italian institute for research and training in the transport sector) [53] showed that trips up to 2 km are made 58% on foot, 8.7% by bike, 1.7% by motorbike, 27% by car, and 3.9% by public transport. In the range between 2 and 10 km, on the other hand, pedestrian trips decrease to 4.6% (over 10 km the value is 0), 4.9% by bike, 72.8% by car, and 13.9% by public transport. Beyond 10 km, the bike is practically not used (0.9%) and the car rises to over 82% of trips. In addition to the effects on the environment, some studies have shown positive effects on human health [54–56]. The main policies that can promote pedestrian mobility are: • Creation of pedestrian areas; • Creation of limited traffic zones; • Creation of 30-zone; • Maintenance and renovation of sidewalks; • Construction of underpasses and overpasses or marked and illuminated pedestrian crossings (increasing the perceived safety); • Construction of mobile infrastructure to assist pedestrian movements (escalators, conveyor belts, lifts). The main policies to promote cycling are: • Construction of cycle paths; • Preparation of parking areas dedicated to bicycles; • Incentives for the purchase of bicycles; • Bike-sharing systems. The literature on all these topics is extensive; here, we refer to some general papers that are useful to deepen the specific topics [57–66]. 3.3. Ecodriving Ecodriving is one of those policies for sustainable mobility also known as “soft policies”. It consists of promoting, in the case of private car drivers, or in providing, in the case of collective transport systems, energy-efficient driving styles that produce, for the same number of km travelled, lower …

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