Figure 6 : Distribution of the included papers in relation to the type of vehicle and the energy
Source : authors
From the total of paper considered, 42% proposed bicycle/tricycle as the best alternative for last mile urban deliveries. Considering these papers, with regard to the energy used, 64% pointed to electric energy and 36% to human propulsion. On the other hand, light commercial vehicles, which are vehicles with a Gross Vehicle Weight (GVW)11Means the value specified by the manufacturer as the loaded weight of a single vehicle. The same criterion is used by the Brazilian authorities. of not more than 3.5 tonnes, were considered in 58% of the studies, among which 73% of them pointed to the use of electricity and 27% of them pointed to the use of other sources of energy (diesel dedicated, diesel/methane and diesel/biodiesel). It is noteworthy that (Alessandrini et al., 2015) considered the use of an unmanned light commercial vehicle powered by electricity. (Foltyński, 2014) suggested the use of bicycles, tricycles and motorcycles together with light commercial vehicles (all electric), as an alternative for last mile delivery.
According to (Schoemaker et al., 2006), the number of light commercial vehicles in Europe has increased by 15% between 1990 and 2003, while the number of vehicles with a GW over 3.5 tonnes has increased by 6.6% during the same period. This information demonstrates the tendency to increase the participation of light commercial vehicles in the urban freight transport. In addition, according to (Dablanc, 2009) urban freight transport is inefficient in most cities, including those in developed countries, with low density rates. For example, in London the occupancy rate of this type of vehicle varied between 40 and 60% in 2006 (Schoemaker et al., 2006). This practice has also been applied in developing countries, such as Brazil, where tricycles have been used by companies like Coca-Cola (Fernandes, 2015a) and Correios (Oliveira, 2015b), which seek to reduce the effects of traffic congestion and traffic restrictions imposed by the authorities, using sustainable practices that guarantee the maintenance or improvement of the level of service.
Therefore, it appears that delivery companies may have a tendency to use smaller vehicles in the last mile distribution, for example, tricycles and bicycles, as verified in this systematic literature review. It is inferred thus a trend, pointed out by the specialized literature, on the reduction of vehicle sizes used in the last mile, whereby the adoption of bicycles, tricycles and light commercial vehicles (Table 2). Nonetheless, it is a logistical challenge to integrate the trend of reducing the size of vehicles (consequently with lower load capacity) in the last mile urban delivery with the operation of regional freight transport that, in pursuit of sustainable and efficient transportation, uses larger and heavier vehicles, with higher capacity (Alice and Ertrac, 2015). For this reason, it becomes essential to use deconsolidation centers around urban areas.
Regarding the type of energy used by vehicles, considering all 26 papers included in this systematic literature review, it was verified that 69% deals with vehicles powered by electricity. This result demonstrates the potential use of electric vehicles in the urban freight transport, especially in the last mile distribution, since electrification is widely considered as a viable strategy for reducing the oil dependency and environmental impacts of road transportation (Weiss et al., 2015). The other types of energy used in the applications analyzed were: methane, biodiesel, diesel (23%) and human propulsion (8%).
It is noted that there is a cultural barrier related to the acceptability of customers for signing contracts with companies that use a bicycle delivery service (Schliwa et al., 2014). Another barrier mentioned refers to the cities infrastructure, especially to electric vehicles power supplies system, and the need for construction of consolidation centers, in order to facilitate the cargo distribution using electric vehicles and smaller vehicles.
Regarding the economic benefits, the studies pointed to the reduction of: energy consumption, delivery time and traffic congestion. The environmental benefits have focused on reducing CO2 emissions, air pollutants and noise emissions. Referring to social benefits, it is possible to highlight jobs generation and the improvement in the quality of life of the population. It is important to reinforce the conclusions of (Sadhu et al., 2014), which pointed out the health problems that could be caused by the use of bicycle (human propulsion) and the excess load weight (some cases about 195 kg).
With reference to the scope of its application, it was possible to obtain information about the average speed developed by the vehicles considered in the studies and the cargo capacity, as well as the characteristics of cities where the studies were applied. The average bicycles/tricycles speed varied from 2 to 6 km/h (Sadhu et al., 2014), while light commercial vehicle reached 25 km/h (Gruber et al., 2014). Regarding cargo capacity, (Gruber et al., 2014) point out the value of 100 kg for capacity on electric bicycles in Germany. (Schliwa et al., 2014) informs the existence of weight limitation of 60 kg for shipments on electric-assisted bicycles in England. However, (Schier et al., 2016), in their survey of the last mile distribution in urban areas, consider that electric-assisted bicycles and tricycles can carry between 50 and 250 kg. In the case analyzed by (Sadhu et al., 2014), in New Delhi, up to 195 kg of human-powered bicycles are transported per trip.
Among the included papers, 81% considers a case study or an application in one or more cities (as shown in Table 3). Berlin, Paris and Tokyo are the most studied cities. Tokio is a megacity with 13.5 million inhabitants, Berlin is the fifth most populous city in Europe with four million inhabitants and a high concentration of economic activities (Demographia, 2016) and Paris has a high population density (21 thousand inhab/km2) and high concentration and diversification of economic activities (Heitz and Beziat, 2016). Only one study considered a megacity located in a developing country: New Delhi (India) with 23 million inhabitants, distributed in its metropolitan region. Although there was a study developed in Brazil, its analysis was developed in Belo Horizonte, which is not one of the two Brazilian megacities (São Paulo and Rio de Janeiro). There was heterogeneity in relation to the population of the studied cities, ranging from 87 thousand to 13 million inhabitants. Moreover, it has been observed that approximately 70% of the cities present densities above 1,000 inhab/km2. This result was an expected, since the demand for urban freight transportation is concentrated in densely populated areas (Heitz and Beziat, 2016).
Table 3. Cities with case studies in decreasing order of density levels