## 3 Research Methodology  
This study extends the preliminary survey of [6] in three areas: (i) the methodology of review and analysis of results are extensively improved with a broader time frame of review, (ii) more than double the amount of reviewed papers, and (iii) more comprehensive classifications. In this study, the review approach is inspired by [21], who based their study methodology of [22], describing four steps of shaping the structure of a review paper. This includes material collection, descriptive analysis, category selection, and material evaluation. Through these steps, review materials are identified, analysed, and classified.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Paper** & **Highlights** & **Year** & **Number of Papers** \\ \hline
[7] & Disaster Relief Routing & 1987–2011 & 29 \\  & Insights on theoretical and practical logistical problem & & \\  & Challenges and modelling aspect of delivery problem & & \\  & Egalitarian \& utilitarian nature delivery policy & & \\ \hline
[8] & Last Mile Delivery \& challenges of routing & 1998–2014 & 24 \\  & Classified by 3 routing objectives \& 4 phases of DM & & \\  & Highlighted difference of solution quality between commercial and disaster application & & \\ \hline
[9] & Overview on modelling and solution of 2-stage stochastic programming: uncertainties in humanitarian operations & 2004–2016 & 40 \\  & Classified papers based on disaster phase, operations \& type of disaster & \\  & Highlighted problematic assumptions in reviewed models & & \\ \hline
[10] & Systematic review of OR in casualty management: classified types of rescue operations & 1977–2019 & 88 \\  & micro-analysis of OR problem including stochastic, dynamic, multi-objectives, etc. & & \\  & Covering all OR problem related, not restricted to routing problem only & & \\ \hline
[11] & Eco-friendly, unmanned electric bus routing problem & 2010–2018 & 57 \\  & multi-depots, time windows, heterogeneity, split delivery \& other complex VRPs & \\ \hline
[12] & Proposed definition for RVRP & 1997–2013 & 50 \\  & Real life attributes including stochastic, dynamic, heterogeneity, multi-periodicity & & \\  & Classified based on the constraint classification from [18; 19] & & \\ \hline
[13] & Decomposition algorithm for exact solution and metaheuristic & 1959–2009 & not specified \\  & Attribute learning through naturally inspired algorithm & & \\ \hline
[17] & Addressed Stochastic and Dynamic VRP & 2001–2015 & not specified \\  & Comparison with each pure stochastic and dynamic counterpart based on uncertain parameters according to [20] & & \\  & Classified paper based on online, offline computation and hybrid of the two & & \\ \hline
[15] & Surveyed 277 papers based on taxonomy proposed by [16] & 2009–2015 & 277 \\  & Shown that metaheuristic is applied the most among the other solutions: exact, heuristic, online solution \& simulation based solution & \\  & Covered multiple attributes of VRPs: split deliveries, multi period VRP, SVRP, DVRP, etc. & & \\ \hline
[6] & Preliminary work of this study & 2010–2017 & 49 \\  & Preliminary review on VRP’s applications in supply and delivery, search and rescue operation, intermodal network, and other applications & & \\  & Brief overview of modelling and solution under preliminary classifications & & \\ \hline This study & Modelling and solution of VRP for humanitarian operations: Supply \& delivery, Evacuation, rescue & 2010–2020 & 123 \\  & Classify papers based on DM phase, disaster types, model characteristics \& solutions & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Related Review Papers.