**3. Literature Review**

The European Conference of Ministers of Transport defines light rail as a rail-borne form of transport that can be developed in stages ranging from the modern tram to a rapid transport system operating on its own right of way, be it underground, at ground level, or elevated [18]. Ideally, light rail is a form of railway urban transportation system, that is not a heavy traditional form of railways. The adoption of light rail in Africa is gaining momentum, as can be seen in Table 1 below.

**Table 1.** Light rail projects in Africa (Source: https://en.wikipedia.org/wiki/Urban\_rail\_transit\_in\_Africa (accessed on 29 December 2019).


The comparison of the basic characteristic of light rail as compared to the traditional rail can be seen in Table 2 below.



Source: adopted from [18].

There is a growing body of literature related to the contributions derived from and the diverse effects of LRT projects in developing cities. Other studies have focused on the societal and commercial consequences of urban rail and light rail transit (LRT) as their main subjects of investigation. Even in the face of biting economic hardships, several developing economies in Sub-Saharan Africa and South Asia have joined the trend and are earmarking railway infrastructure projects in their strategic development plans for the next 10 to 30 years [19]. Railway infrastructure ventures are a paramount gesture and indicate one of man's greatest innovations towards the achievement of Sustainable Development Goals. Africa's commitment towards the development of RLT services is presented in Table 3 below.

*Sustainability* **2021**, *13*, 5667


**Table 3.** Light Rail projects by region and implementation status.

Sustainable Development (SD), as explained in the United Nations World Commission on Environment and Development acknowledging the 1987 Brundtland Commission report: "is the development that meets the needs of the present without compromising the ability of future generations to meet their own needs" [8,21–25]. According to [26], sustainability is synonymous with sustainable development. This implies that sustainability and sustainable development [27] are used interchangeably, as is the case in this paper. Elkington (1997) synthesized these dimensions as the Triple-P or the Triple Bottom Line. The United Nations 2005 World Summit Outcome Document refers to the "interdependent and mutually reinforcing pillars" of sustainable development as economic development, social development, and environmental protection [28]. Sustainable development is mostly interpreted and understood in the context of the triple bottom line approach as indicated in Figure 2 below. The SD theory, made popular through practice, is inseparable from relevant policies implementation [29] and may involve the assessment of stakeholder perceptions.

**Figure 2.** Percentages of CO2 release in the transport sector. Source: International transport forum, Transport greenhouse gas emission 2010, [28].

The need for sustainability has emerged in this context [30] and the concept of sustainability, popularized in recent years, is unquestionably increasingly perceived as a necessary tool for understanding the social, economic, and environmental consequences linked to projects and project management [31].

However, some researchers approach sustainability differently and consider it to be composed of several other dimensions [26] with other dimensions or principles considered such as risk reduction, stakeholder, and accountability [32].

Environmental sustainability impacts to transport are geared towards attaining a reduction in local atmospheric pollution, global warming, negative impact on plants and animals, the impact of solid waste disposal on the environment, etc. [8]. Socially, sustainable urban transportation is concerned with delivering satisfactory access to transport with the objective of curtailing social exclusion, and progresses an individual's quality of life [8,33]. The social aspects can encompass corporate governance, human capital development, human rights, labor practices, relation with employees, and working conditions, safety, engagement of stakeholders, and decent work. The economic aspect involves return on investment, business agility, risk reduction, risk reduction, cost management, honest price, and service, project reporting, and investment evaluation. It has been clearly documented that in the contemporary economy, transport is pivotal due to its effects on social, and economic development [34].

This implies, therefore, that a properly functioning, and modern transport system leads to sustainable development as all other sectors such as power, industry, health, and construction at one-point need to depend on transport for their delivery. In fact, the greatest priority of sustainable transport is to ensure effective and efficient mobility of goods and people, while at the same time contributing to the realization of economic, social, and environmental sustainability dimensions as shown in Figure 2. The International Union of Railways (UIC) declaration and indicators of sustainable mobility and transport provide the areas in which railways are contributing to sustainability. Spill-over sustainability contributions are not mentioned.

Railways certainly have a crucial role in a sustainable, safer, and greener evolution of the transport system [34–36]. Light rails can play a significant role to reduce the environmental impact of any city through providing efficient and effective transport with low environmental consequences, which in the end helps to fashion a more sustainable approach to transport.

Railways as the backbone of sustainable transport make strong connections to a number of the SDGs and supporting targets, notably; energy efficiency (Goal 7), resilient infrastructure (Goal 9) and access to sustainable transport (Goal 11) [37], resilience to climate-related hazards (Goal 13), and promote environmentally sound technologies and multi-stakeholder partnerships (Goal 17) [38].

According to the international transport forum, Transport greenhouse gas emission 2010, within the transport sector, energy consumption and therefore CO2 emissions are dominated by road, followed by aviation and shipping. Rail accounts for 2% of CO2 emissions within the transport sector as indicated in Figure 3 below. This, therefore, implies that railways are the good performers towards environmental sustainability in the transport sector.

**Figure 3.** Percentages of CO2 release in the transport sector. Source: International transport forum, Transport greenhouse gas emission 2010, [28].

Transport carbon dioxide emissions 2008.

This claim is further verified by data collected from 28 EU nations and was published in 2014, The collected data as indicated in Figure 4 below projects railway transport as the best performer contributing, only 7 million tonnes of CO2 emissions with road transport leading at 833.3 million tonnes.

In discussing the findings of their study, [40] suggest that the construction of Urban Rail Transit has played an important role in realizing great-leap-forward development of economy and improving the urban economic structure and has become the source impetus for fueling urban economic growth. They further describe in detail three effects as (1) it leads the transformation of economic development way, (2) construction provides broad development space for environmental protection industry, and (3) construction improves the city's soft power. The need now is to quantify some of these effects that this paper intends to perform as well. Alade et al. [8] asserts that excluding the economic profits, the environmental and social development benefits are also derived from rail system ventures. The authors of this paper, therefore, believe that apart from the targets of railways that

include: climate protection, energy efficiency, exhaust emissions, noise, and vibrations [41], railways have much to offer in support of sustainable development.

**Figure 4.** Comparison of transport performance by mode and respective CO2 emissions in EU-28 countries (EC, 2014). Source: [39].
