Marlin Ulmer

Otto-von-Guericke University Magdeburg | OvGU · Faculty of Economics and Management

How to best deliver goods to consumers has been a logistics question since time immemorial. However, almost all traditional delivery models involved a form of company employees, whether employees of the company manufacturing the goods or whether employees of the company transporting the goods. With the growth of the gig economy, however, a new mode...

Home repair and installation services require technicians to visit customers and resolve tasks of different complexity. Technicians often have heterogeneous skills and working experiences. The geographical spread of customers makes achieving only perfect matches between technician skills and task requirements impractical. Additionally, technicians...

Restaurant meal delivery has been rapidly growing in the last few years. The main challenges in operating it are the temporally and spatially dispersed stochastic demand that arrives from customers all over town as well as the customers' expectation of timely and fresh delivery. To overcome these challenges a new business concept emerged, "Ghost ki...

Vans, cargo bikes, or even autonomous delivery vehicles are used in urban parcel delivery. A fleet consisting of these vehicles is called heterogeneous, differing in several technological dimensions including speed, range, as well as the impact on the delivery process. This research analyzes the operations of such a heterogeneous fleet in express u...

Because customers must usually arrange their schedules to be present for home services, they desire an accurate estimate of when the service will take place. However, even when firms quote large service time windows, they are often missed, leading to customer dissatisfaction. Wide time windows and frequent failures occur because time windows must b...

We consider a service provider performing pre-planned service for initially known customers with a fleet of vehicles, e.g., parcel delivery. During execution, new dynamic service requests occur, e.g., for parcel pickup. The goal of the service provider is to serve as many dynamic requests as possible while ensuring service of all initial customers....

An increasing number of local shops offer same-day delivery in order to compete with the online giants. However, the distribution of parcels from individual shops to customers reduces the rare consolidation opportunities in the last mile even further. Thus, shops start collaborating on urban same-day delivery by using shared vehicles and micro-depo...

Taxi-ridesharing systems are considered an important means for sustainable urban transport. Previous literature shows that introducing meeting points in ridesharing, where customers are picked up and dropped off, increases its performance. We consider an on-demand taxi-ridesharing system, where the focus lies on the anticipatory assignment of custo...

In ride-sharing systems, platform providers aim to distribute the drivers in the city to meet current and potential future demand and to avoid service cancellations. Ensuring such distribution is particularly challenging in the case of a crowdsourced fleet, as drivers are not centrally controlled but are free to decide where to reposition when idle...

We consider an integrated planning problem that combines purchasing, inventory, and inbound transportation decisions in an agri-food supply chain where several suppliers (farmers) offer a subset of products with different selling prices and available quantities. We provide a mixed-integer programming formulation of the problem and a matheuristic de...

The availability of various services for individual mobility is increasing, especially in urban areas. Dynamic ride-hailing services address these aspects and are gaining market share with providers such as MOIA, UberX Share, Sprinti or BerlKönig. To be able to offer competitive pricing for such a service and at the same time provide a high service...

The demand for same-day delivery (SDD) has increased rapidly in the last few years and has particularly boomed during the COVID-19 pandemic. The fast growth is not without its challenge. In 2016, due to low concentrations of memberships and far distance from the depot, certain minority neighborhoods were excluded from receiving Amazon’s SDD service...

There has been a paradigm-shift in urban logistic services in the last years; demand for real-time, instant mobility and delivery services grows. This poses new challenges to logistic service providers as the underlying stochastic dynamic vehicle routing problems (SDVRPs) require anticipatory real-time routing actions. The complexity of finding eff...

Eco-labels are a way to benchmark transportation shipments with respect to their environmental impact. In contrast to an eco-labeling of consumer products, emissions in transportation depend on several operational factors like the mode of transportation (e.g., train or truck) or a vehicle’s current and potential future capacity utilization when new...

We consider an urban instant delivery environment in which customers place orders over the course of the day and are promised delivery within a short period of time after an order is placed. The orders are fulfilled from a single facility and deliveries are made using a fixed fleet of vehicles with vehicles performing one or more delivery trips dur...

Peer-to-peer transportation platforms dynamically match requests (e.g., a ride, a delivery) to independent suppliers who are not employed nor controlled by the platform. Thus, the platform cannot be certain that a supplier will accept an offered request. To mitigate this selection uncertainty, a platform can offer each supplier a menu of requests t...

How to best deliver goods to consumers has been a logistics question since time immemorial. However, almost all traditional delivery models involved a form of company employees, whether employees of the company manufacturing the goods or whether employees of the company transporting the goods. With the growth of the gig economy, however, a new mode...

This survey article provides an overview on future directions for research in urban mobility and city logistics. It sets a focus on three particularly serious changes in the business models: vehicle autonomy, crowdsourced logistics, and urban micro‐consolidation centers. In the future, service fleets might fully or partially be autonomous which bri...

Eco-labels are a way to benchmark transportation shipments with respect to their environmental impact. In contrast to an eco-labeling of consumer products, emissions in transportation depend on several operational factors like the mode of transportation (e.g., train or truck) or a vehicle's current and potential future capacity utilization when new...

Local delivery platforms are collaborative undertakings where local stores offer instant-delivery to local customers ordering their products online. Offering such delivery services both cost-efficiently and reliably is one of the main challenges for local delivery platforms, as they face a complex, dynamic, stochastic dynamic pickup-and-delivery pr...

Stochastic dynamic vehicle routing problems have become an essential part of logistics and mobility services. In such problems, a sequence of vehicle routing decisions have to be made in reaction and anticipation of newly revealed stochastic information. To this end, a variety of computational operations research methods has emerged in the literatu...

In this paper, we consider same-day delivery with vehicles and drones. Customers make delivery requests over the course of the day, and the dispatcher dynamically dispatches vehicles and drones to deliver the goods to customers before their delivery deadline. Vehicles can deliver multiple packages in one route but travel relatively slowly due to th...

In this paper, we consider same-day delivery with a heterogeneous fleet of vehicles and drones. Customers make delivery requests over the course of the day and the dispatcher dynamically dispatches vehicles and drones to deliver the goods to customers before their delivery deadline. Vehicles can deliver multiple packages in one route but travel rel...

There has been a paradigm-shift in urban logistic services in the last years; demand for real-time, instant mobility and delivery services grows. This poses new challenges to logistic service providers as the underlying stochastic dynamic vehicle routing problems (SDVRPs) require anticipatory real-time routing actions. Searching the combinatorial a...

We consider a stochastic dynamic pickup and delivery problem. A fleet of drivers delivers food from a set of restaurant to spontaneously ordering customers. The objective is to dynamically control a fleet of drivers in a way that avoids delays with respect to customers deadlines. The sources of stochasticity for this problem are twofold: first, the...

Restaurant meal delivery companies have begun to provide customers with meal arrival time estimations to inform the customers' selection. Accurate estimations increase customer experience while inaccurate estimations may lead to dissatisfaction. Estimating arrival times is challenging because of uncertainty in both delivery and meal preparation pro...

The demand for same-day delivery (SDD) has increased rapidly in the last few years and has particularly boomed during the COVID-19 pandemic. Existing literature on the problem has focused on maximizing the utility, represented as the total number of expected requests served. However, a utility-driven solution results in unequal opportunities for cu...

Operations research requires models that unambiguously define problems and support the generation and presentation of solution methodology. In the field of dynamic routing, capturing the joint evolution of complex sequential routing decisions and stochastic information is challenging, leading to a situation where rigorous methods have outpaced rigo...

Stochastic and dynamic vehicle routing problems gain increasing attention in the research community. In these problems, routing plans are dynamically updated based on realizations of stochastic information. Due to the complexity of the corresponding Markov decision processes (MDPs), the calculation of optimal policies for these problems is usually...

Using crowdsourced delivery capacity, i.e., individuals offering their vehicle and their time to perform deliveries, can allow companies to provide faster delivery options and to more easily accommodate fluctuations in demand. However, because of the uncertainty associated with crowdsourced delivery capacity, it makes ensuring service quality more...

With a growing number of services provided at or to a customer's home, the familiarity of the service provider, or driver, with the customer's location is increasingly important. One prominent example is retail distribution, where familiarity with the delivery location can save the driver time. In contrast to other kinds of familiarity (e.g., tasks...

We address the operational management of station-based bike sharing systems (BSSs). In BSSs, users can spontaneously rent and return bikes at any stations in the system. Demand is driven by commuter, shopping, and leisure activities. This demand constitutes a regular pattern of bike usage over the course of the day but also shows a significant shor...

In this paper, we consider service applications where drivers serve subscription customers at their homes on a regular basis and at known times. To build trust with customers, the company requires that subscription customers are consistently served by the same driver. In addition to subscription customer, on-demand customers request delivery on a d...

With the rise of new business models that require real-time decision making, anticipatory decision making becomes necessary to use the available resources wisely. Dynamic real-time decision problems occur in many business fields, for example in vehicle routing applications with customer service requests that are unknown and expect a fast response....

In this paper, we introduce a novel method of value function approximation (VFA). In stochastic, dynamic decision problems, VFAs approximate the reward-to-go. Conventionally, VFAs are either parametric or non-parametric. Parametric VFAs (P-VFAs) approximate the value function using a particular functional form. Non-parametric VFAs (N-VFAs) approxim...

Same-day delivery has become a very important challenge for e-commerce providers. However, effective business models are still not established. In this paper, we analyze the potential of combining parcel pickup stations and autonomous vehicles for same-day delivery. This combination may allow for consolidation of goods, automated delivery processes...

An increasing number of e-commerce retailers offers same-day delivery. To deliver the ordered goods, providers dynamically dispatch a fleet of vehicles transporting the goods from the warehouse to the customers. In many cases, retailers offer different delivery deadline options, from four-hour delivery up to next-hour delivery. Due to the deadlines...

Due to new business models and technological advances, dynamic vehicle routing is gaining increasing interest. Especially solving dynamic vehicle routing problems with stochastic customer requests becomes increasingly important, for example, in e-commerce and same-day delivery. Solving these problems is challenging, because it requires optimization...

In this paper, we analyze how drones can be combined with regular delivery vehicles to improve same-day delivery performance. To this end, we present a dynamic vehicle routing problem with heterogeneous fleets. Customers order goods over the course of the day. These goods are delivered either by a drone or by a regular transportation vehicle within...

We present the stochastic-dynamic inventory routing problem for bike sharing systems (SDIRP). The objective of the SDIRP is to avoid unsatisfied demand by dynamically relocating bikes during the day. To anticipate potential future demands in the current inventory decisions, we present a dynamic lookahead policy (DLA). The policy simulates future de...

Although increasing amounts of transaction data make it possible to characterize uncertainties surrounding customer service requests, few methods integrate predictive tools with prescriptive optimization procedures to meet growing demand for small-volume urban transport services. We incorporate temporal and spatial anticipation of service requests...

In this paper, we explore same-day delivery routing and particularly how same-day delivery vehicles can better integrate dynamic requests into delivery routes by taking advantage of preemptive depot returns. A preemptive depot return occurs when a delivery vehicle returns to the depot before delivering all of the packages currently on-board the veh...

Service providers dispatch vehicles to provide technical services or deliver goods. In many cases, customers must be present when the provider arrives, and customers are given a time window in which the service or delivery will take place. These time windows must often be given at the time of the request. However, at the time of the request, not al...

Traffic pollution is an increasing challenge for cities. Emissions such as nitrogen dioxides pose a major health threat to the city's inhabitants. These emissions often accumulate to critical levels in local areas of the city. To react to these critical emission levels, cities start implementing dynamic traffic management systems (TMS). These syste...

In practical applications like parcel or technician services, customers request service during the day. Service providers decide whether to accept a customer for same-day service or to defer a customer due to resource limitations. Some requests are therefore postponed to the following day. To satisfy customer expectations, service providers aim on...

Delivery companies are affected by emission-sensitive traffic management systems. These systems are installed in cities to react instantly to emission hot-spots through adapting traffic light programs at intersections. This results in a change of the travel times for the delivery vehicle. In this paper, we model the problem in a dynamic vehicle rou...

In many service applications, customers can request service dynamically during the service time horizon and may be served the same day. For the service provider, these requests are stochastic and due to working hour limitations, usually not all customer requests can be accepted for same-day service. Decisions are made about service acceptances and...

In this paper, we study the Dynamic Vehicle Routing Problem with Stochastic Customers (DVRPSC), a common problem setting for Courier, Express and Parcel service providers. We focus on the case in which a dispatcher must decide which dynamically occurring customer requests should be confirmed and how to integrate these into the existing tour of a ve...

Delivery companies offer same-day delivery (SDD) in more and more cities. SDD defines a business model in which a customer order is fulfilled the same day it is issued. To gain a competitive advantage, companies start offering increasingly narrower delivery deadlines of a few hours length. Currently, many companies struggle to cost-efficiently main...

Ubiquitous computing technologies and information systems pave the way for real-time planning and management. In the process of dynamic vehicle dispatching, the adherent challenge is to develop decision support systems using real-time information in an appropriate quality and at the right moment in order to improve their value creation. As real-tim...

Parcel services route vehicles to pick up parcels in the service area. Pickup requests occur dynamically during the day and are unknown before their actual request. Because of working hour restrictions, service vehicles only have a limited time to serve dynamic requests. As a result, not all requests can be confirmed. To achieve an overall high num...

We present a literature review of and modeling framework for dynamic vehicle routing problems (DVRPs). Our review yields two key findings. First, DVRP papers often lack models of the underlying stochastic and dynamic problems that they study. Second, the overwhelming majority of DVRP solution methods employ route plans, a potential course of action...

Bike sharing systems have been launched in many cities. Such systems consist of stations allowing users to rent and return bikes. Due to spatio-temporal variation of requests, stationstend to either be empty or full of bikes. At empty stations, no bikes can be rented while at full stations bikes cannot be returned. The global goal is tosatisfyall r...

In the field of dynamic vehicle routing, the importance to integrate stochastic information about possible future events in current decision making increases. Integration is achieved by anticipatory solution approaches, often based on approximate dynamic programming (ADP). ADP methods estimate the expected mean values of future outcomes. In many ca...

Bike sharing systems (BSS) provide individual and eco-friendly urban mobility and are implemented in a growing number of cities. In BSS, customers can rent and return bikes spontaneously at stations and at every time of the day. To allow a reliable usage, system operators have to enable a sufficient number of bikes and empty bike racks at each stat...

In city logistics, courier express and parcel services (CEP) deal with last mile deliveries in an urban environment. CEP route vehicles to deliver parcels to costumers distributed in the cities area. Customers expect fast and reliable services to reasonable prices. As a result, CEP have to plan and execute their routing efficiently. In a city logis...

In many dynamic vehicle routing applications, anticipation of the future is essential for efficient and effective decision making. In order to incorporate possible future events into current decision making, it is necessary to evaluate every decision’s impact to the overall objective. This is typically achieved by an evaluation of the post-decision...

In the field of dynamic vehicle routing, the importance to integrate stochastic information about possible future events in current decision making increases. Integration is achieved by anticipatory solution approaches, often based on approximate dynamic programming (ADP). ADP methods estimate the expected mean values of future outcomes. In many ca...

Parcel services route vehicles to pick up parcels in the service area. Pickup requests occur dynamically during the day and are unknown before their time of request. Due to working hour restrictions, vehicles are provided with a limited time budget to serve dynamic requests. As a result, not all requests can be confirmed. To achieve an overall high...

City logistic service providers often have to decide under uncertainty. In some cases, not all customers are known at the time of the decision, but may request service in the course of day. Here, anticipation of possible future requests in current decision making is mandatory to avoid ineffective decisions and to serve a high amount of requests wit...

Due to varying traffic volumes and limited traffic infrastructure in urban areas, travel times generally are uncertain and differ during the day. In this environment, city logistics service providers (CLSP) have to fulfill deliveries cost-efficient and reliable. To ensure cost-efficient routing while satisfying promised delivery dates, information...

In recent years, the number of challenges for courier, express and parcel services has grown. Today, service providers deal with dynamic changes and uncertainty. Customers can request service at any point of time in the whole service region. Technologies like Global Positioning Systems allow a more detailed and dynamic routing. Furthermore, histori...