type specific vehicles to serve that demand. A common practical application of this routing problem is found in health-
care transport. In Parragh (2011) and Parragh et al. (2012) the authors describe a DARP with heterogeneous demand
and vehicles for the transportation of patients and disabled people. In their model vehicles may be equipped with staff
seats, patient seats, stretchers and wheelchair places which in turn define the demand type and capacity for each vehi-
cle. Another form of heterogeneous routing problems is considered by Rekiek et al. (2006) and Melachrinoudis et al.
(2007) where different vehicles in terms of capacity are utilized to serve a single type of demand. This problem is
closely related to mixed vehicle routing problems, which do not consider pickup and drop offpositions for each re-
quest. In comparison to these heterogeneous routing problems the model proposed in this work allows for an en-route
change in vehicle configuration. In the previously studied heterogeneous routing problems, the vehicle configuration is
decided upon before the depot departure and remains the same until the vehicle returns to the depot. Additionally, the
number of configuration changes is not limited, allowing for several configurations for a given route. In Qu and Bard
and Tellez et al. the authors present heterogeneous PDP and DARP with configurable vehicles, respectively. In these
works vehicles can reconfigure their interior and, by that, change the capacity of the vehicle. The others propose a
mixed-integer program which is solved using an ALNS in both papers. In Qu and Bard the authors analyze several
scenarios and conclude that cost savings of 30%-40% can be achieved by changing the configuration of the vehicles.
The Swap Body Vehicle Routing Problem (SB-VRP) was introduced as part of an operations research computation
challenge and has been solved by several research teams, for example (Huber and Geiger, 2017; Todosijevi´c et al.,
2017; Toffolo et al., 2018). In essence, the problem considers the routing of trucks, which can attach or remove
trailers of a certain length. The nature of this problem is similar to the here proposed MP-PDP. However, in the SB-
VRP the start and end depot for a trailer has to be one and the same, whereas in the MP-PDP a module can be loaded
and dropped at any depot or service depot, hence embracing a more general and flexible functionality. Furthermore,
no multi-depot functionality is implemented in the original problem formulation. Additionally, the SB-VRP can deal
with two different types/sizes of trailers whereas the proposed work here can be easily extended to consider more
vehicle types, e.g. passenger, freight, and waste transportation. Finally, the proposed vehicle routing problem extends
the SB-VRP by adding additional constraints, such as maximum range per platform.
The third group of related vehicle routing problems are the trailer and transshipment problems (Drexl, 2013). In
addition to an adjusted objective function formulation, several additional constraints capturing the multi-depot con-
siderations in the proposed MP-PDP formulation create a new problem variant. In truck-and-trailer routing problems
only freight demand is typically considered (Derigs et al. (2013) and Parragh and Cordeau (2017)). Moreover, the
types of trailer are limited to one; hence, only the addition or removal of trailers is considered. In contrast, the MP-
PDP allows for the investigation of several demand type-specific modules, each of which having a different capacity.
Li et al. (2014) investigate if another mode of passenger transportation, namely private taxi rides, can be used for
integrated urban transportation. The authors propose a reduced version of the Share-a-Ride problem and the Freight
Insertion problem. The problem minimizes the additional operating costs of adding freight items in a set of planned
taxi trips. The authors solve their proposed mixed-integer linear program (MILP) for static and dynamic demand
scenarios. The numerical results are sensitive to the spatial distribution of the freight demand. The authors conclude
that the integration of freight items into taxi services is a promising solution for urban areas. However, this new
integrated mode should be complemented by a traditional truck service to guarantee the delivery of all packages.
Schr¨oder and Liedtke (2017) present a multi-agent simulation model for passenger and freight transportation. They
investigate the impacts of various policy measures, i.e. special vehicle tolls.
Since the computational complexity of vehicle routing and scheduling problems has proven to be NP-hard (Lenstra and Kan,
1981), it is challenging to efficiently solve these problems for larger scenarios. Two general approaches are typically
used to solve the VRP and its variations: (i) the utilization of exact analytical algorithms (e.g. Branch-and-Cut,
Branch-and-Bound) and, (ii) the development of problem-specific heuristics or meta-heuristic algorithms (e.g. Sim-
ulated Annealing, Artificial Bee Colony, Genetic Algorithm or Large Neighborhood Search). In Arslan et al. (2016)
a crowd-sourced delivery system for parcels and passengers is solved using an exact solution approach. An exact
algorithm for the shared ride problem is presented by Beirigo et al. (2018), while Ghilas et al. (2016b) solve the PDP
with time windows and scheduled lines using CPLEX.
Due to the computational complexity of VRP problems, most researchers implement heuristic algorithms to solve large
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