# A Review of Literature on Vehicle Routing Problems of Last-Mile Delivery in Urban Areas
## 5 Implications and Future Research
### Result Summary  
This review research identified the problem nature, important considerations, and solution methods in the LMD literature under four categories: crowdshipping, parcel lockers, sidekick delivery, and optional delivery points. * Crowdshipping utilizes sharing economy platforms for parcel delivery. Occasional drivers make their resources available for parcel delivery, offering cost-effective LMD solutions. This paradigm thrives on the efficiency and flexibility of the drivers. De \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Ref.** & **Problem Nature** & **Important Considerations** & **Objectives** & **Sample Size** & **Solution Method** \\ \hline \multirow{10}{*}{[134]} & & & - & If a delivery cannot be made in a defined time window, it will be delivered to the other optional point & Minimize the overall cost of selected routes & - & 25-50 requests & Exact solve (branch price and cut) \\  & - & \begin{tabular}{c} \\ - \\ - \\ \end{tabular} & - & \begin{tabular}{c} - \\ - \\ - \\ \end{tabular} & \begin{tabular}{c} - \\ - \\ - \\ \end{tabular} & \begin{tabular}{c} - \\ - \\ - \\ \end{tabular} & \begin{tabular}{c} 25-50 requests \\ - \\ - \\ \end{tabular} & \begin{tabular}{c} Exact solve \\ (branch price and cut) \\ \end{tabular} \\ \cline{1-1}  & - & Time & - & \begin{tabular}{c} - \\ - \\ - \\ \end{tabular} & \begin{tabular}{c} Vehicles and lockers, as \\ optional points, have \\ limited capacities \\ \end{tabular} & & & & & \\ \hline \multirow{10}{*}{[135]} & & & - & Vehicles have limited & & & & \\  & & & volumes & & & & \\  & & & - & Deliveries should be & & & \\  & & & made within the required & & & & \\  & & & time & & & \\  & - & - & Deliveries cannot be split & & & & \\  & - & \begin{tabular}{c} Time \\ - \\ - \\ \end{tabular} & - & \begin{tabular}{c} - \\ - \\ - \\ \end{tabular} & \begin{tabular}{c} Deliveries cannot be split \\ between two vehicles \\ - \\ - \\ \end{tabular} & \begin{tabular}{c} Minimize travel costs \\ - \\ - \\ \end{tabular} & - & No. of items 20–20 k & Heuristic (hybrid \\ - & No. of points 5–200 & CLP/MP) \\  & - & \begin{tabular}{c} Heuristic (hybrid \\ CLP/MP) \\ \end{tabular} \\  & - & \
\begin{tabular}{c} Heuristic (hybrid \\ CLP/MP) \\ \end{tabular} \\  & - &
\begin{tabular}{c} Heuristic (hybrid \\ CLP/MP) \\ \end{tabular} \\ \cline{1-1}  & - & Stochastic & - & Vehicles have limited & & & & \\  & - & Capacitated & & & & \\  & - & Time & - & Vehicles are allowed to & & \\  & & use limited daily fuel and & & & & \\  & & & should come back to & & & \\  & & & depot (GVRP) & & & \\  & & - & Delivery should be made & & & \\  & & in a specific time span & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._spite the highly dynamic and stochastic nature of the problem, these issues have not been discussed in depth in the literature. Various matching mechanisms have been proposed. Delivery to parcel lockers offers a promising solution for LMD under urban logistics. Distributors place customers' parcels in lockers and notify them for pickup. parcel lockers are expected to reduce cost and environmental hazards while enhancing security and privacy. The assignment of customers to parcel lockers is an important decision for the network design. Various configurations of lockers are proposed: stationary, temporary, and mobile lockers. Time window consideration for busy areas is another emerging aspect of profit generation and customer satisfaction. Delivery by using sidekicks is a specialized category within LMD, taking full advantage of automation, data communication, and sensor technologies. Main vehicles carry sidekicks (mostly aerial drones) and parcels to intermediate locations and deploy sidekicks, getting the benefit of multiple fleet modes. Careful coordination of vehicles is essential. Fleet capacity, battery life, and coverage limitation are considered important. Delivery to optional points invites customers to participate in the delivery planning; customers offer alternative drop locations for the shippers to choose from.