Transportation Geography and Network Science/Last mile problem

Definition.
Last mile is defined as a term to refer the movement of passenger or goods from a transportation hub to the final destination in transportation planning and supply chain management. The last mile is also used in the telecommunications industry as the connecting between the main telecommunication network and individual homes. The last mile problem has become an important study filed with the significant growth of business to consumer deliveries due to the development of e-commerce industry. The challenges to solve the last mile problem includes efficiency and infrastructure improvement, transparency ensure, and cost minimize. 
History.
The last mile problem was firstly raised in the telecommunications industry to refer the difficulty to connect individuals’ home and business with the main telecommunication network. The wire or cable used by the end user is the last mile of the network connection. To ensure connections of all end users, the installation and maintenance of the last mile cable and infrastructure is inevitable which leads to a large amount of work and high cost distributed to end users. The supply chain management also has to face the last mile problem. In the initial transportation phase of freight networks, parcels will be delivered to a central hub, in this stage ships, planes and large trucks can be used for the delivery which is cheap and efficient. After the parcels arrives at the central hub, they will be delivered to each individual consumer by using of smaller trucks since consumers are widely distributed in the city which causes the high cost in the last mile delivery. Similarly, this problem is also existing in transportation networks as the difficulty for passengers to reach their final destination from airports or train station and generally has an inefficiency and high cost in the last mile travel.
The related problems and solutions in last mile.
Transporting goods with using of container ships and freight rail networks is generally the cheapest and the most efficient way. However, since the goods have to be delivered to the final destination, the transportation of goods from freight station to the consumers have to use smaller vehicles and deliver them one by one manually, which is less efficient and occupied the 41% of the total cost of the goods transportation even through the last mile deliveries have a relative short distance to transport. There are also some related problems in last mile delivery. One of the typical problems is transporting goods to the area need of humanitarian. The transportation of goods and supplies are emergence, however, the distribution of the goods from a central transportation hub to the affected area are difficult due to damaged road by a natural disaster. In addition, the unattended package is another challenge in last mile delivery. Many shipping companies tend to leave parcels unattended outside the building if the receiver cannot be contacted, which leads to the risk of occurring of steals and parcel damage due to the exposedness under weather. The application of smart lockers is one of the solutions for this issue, which is designed to keep packages until customers collect them. This approach cannot only protect the missing and damage of the attended parcels but also allow companies to deliver them to one location instead of distributing them to each individual home. Some companies also provide optional choice to customers to pick up parcels from the stores. 
In transportation networks, many passengers might also have difficulty to access a transportation hub from their starting points, which is referred as the first mile problem. The land-use pattern of the United States has showed the movement of jobs and residents to lower-density suburbs which cannot be completely covered within walking distance by public transportation networks. In most of time, passengers tend to drive to reach those areas instead of taking public transportation, which aggravates the reliance of people on private cars and causes the growth of pollution, traffic congestion and urban sprawl. Shared mobility is a main solution for the last mile problem in transportation networks which has been widely adopted in the world. The shared mobility system allows transit in low-density areas become practical, since passengers can easily access sharing stations near transportation hub to using sharing bikes or cars to travel to their final destinations instead of walking. 
Typologies of last-mile deliveries.
According to Roel Gevaers, this typology was developed to describe and analyze the characteristics of the last-mile deliveries by classifying sub-flows of the last mile. According to the different deliver types and order fulfillment, the typology is divided into four sub-types: semi-extended supply chains, decoupled supply chains, full extended supply chains and centralized supply chains. The fully extended supply chain referred the traditional delivery method which pick up goods from retail stores and deliver them directly to each customer. The semi-extended use stores for goods picking which is the same as the fully extended supply chain, however, the reception is indirect which requires customers to collect goods from stores or collection points. The centralized extended supply will also directly deliver goods to customers’ homes; however, the whole delivery process will consist two stages. The goods will be distributed to the distribution center in each area first with using of large trucks, and then deliver them to individual customer, which is efficient to reduce cost of the last mile deliver. The application of smart lockers is a typical decoupled supply chain method, goods will first be delivered to lockers settled in each area and allow customers to pick it up by themselves. It is a feasible solution for the last mile problem which decrease the delivery cost for companies and guarantee the convenience of customers to receive goods at meanwhile.
The case study of the usage of smart lockers.
The smart lockers have witnessed a quick development during these years driven by the growth of online retailing industry. Based on incomplete industry statistics, there is more than 2000 smart locker stations settled in Shenzhen, a southern city in China. A few market stakeholders are competing for the local market share in the last mile delivery industry, among them, Sposter and eStation are the fore runners. The figure below shows the geographical distribution of locker stations in Shenzhen, the circle and rectangle spots present the locations of installed locker stations of two brands, and the colors in each area from dark to light present the local population from high to low. Tt can be clearly observed that the density of installed locker stations is much higher in central areas with high population density then suburb areas However, as the demand of lockers in central area gradually become saturation. Some brands turn to the communities in suburbs area because the local residents tend to purchase a larger range of items from online retailers due to the undesirable commercial environments in suburb. Moreover, the insufficient of delivery service and the large scale of streets in suburb lead to willingness of delivery men to pay the usage fee for avoiding unnecessary waiting time and delivering more goods. The more vacant space for installing locker stations also increase the commercial potential of smart lockers in usage of suburb areas. 
Transit-oriented development.
Transit-oriented development (TOD)is another solution for the last mile problem in urban planning phrase which is aiming to improve the symbiotic relationship between compact urban form and public transport by maximizing the amount of business, residential and communal facilities within walking distance of public transport. The figure below shows the basic concept of the TOD community. The transit station (such as light rail or bus stop and a train station) is centrally located and surrounded by high density and mix used residential and commercial areas. 600 meters are considered as an appropriate scale for pedestrians, and the TOD communities are designed to locate within the range from a transit station. A TOD city is referred the urban pattern which consists a number of TOD communities built on the transit line. The key characteristics of a TOD community can be included as walk-able, compact and center of a destination. The center of a destination means a transit center with divers and mixed-use development. Compact and Walk-able refer to the high density of land use near a transit center and a friendly pedestrian environment provided by a TOD community which is helpful to reduce people’s reliance on private cars due to the last mile problem and slow urban sprawl.