Date of Award

12-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Industrial Engineering

Committee Chair/Advisor

Dr. William G. Ferrell

Committee Member

Dr. Mary E. Kurz

Committee Member

Dr.Thomas C. Sharkey

Committee Member

Dr. Nathan Huynh

Abstract

Modern logistics has increasingly grown into complex interconnected networks to reliably transfer freight between any corners of the world. Today, freight transport must meet the stringent requirements of extremely quick deliveries with competitively low shipping costs and pristine handling. Therefore, logistic services have put immense effort into increasing the efficiency and sustainability of supply chains to meet customer needs. A logistic practice known as cross-docking has been extensively used to perform the function of product consolidation and distribution with reduced costs. Cross-docking is a simple practice of directly transporting material from one truck to another truck at a facility while avoiding or drastically reducing the use of intermediate storage space. The facilities which follow this practice of material handling are known as cross-docks. At cross-docks, instead of storing inventory for extended periods of time, a receiving truck can accept freight straight from the unloading truck. This results in reduced costs of maintaining inventory and faster transit of goods at cross-docks. A cross-dock is used to consolidate freight from multiple sources into a single delivery with common destination or break up freight from a single source to supply multiple destinations. The dissertation addresses various problems related to cross-docks for practical applications.

The dissertation starts with a cross-dock problem where inbound trucks unload freight and supply them to outbound trucks. The cross-dock problem schedules the entry and departure of these trucks at a cross-dock to minimize total delays faced by outbound trucks in receiving its complete demand. Chapter 2 first compares the usual and an alternative operational policy at crossdocks. Cross-docks usually allocate separate doors for unloading inbound trucks and loading outbound trucks. The alternative approach imparts flexibility by allowing both inbound and iii outbound trucks at any door in the cross-dock. Numerical experiments are run to find out if door flexibility can allow faster unloading and loading of goods and hence reduce delays faced by outbound trucks. Next, Chapter 2 also studies the impact of delays with limited material handling equipment (e.g. forklifts) inside the cross-dock. The findings from numerical experiments show the number of forklifts required to avoid excessive delays from their lack of availability.

Chapter 3, next addresses the concern of scheduling trucks at a cross-dock where inbound trucks sometimes cannot arrive at their scheduled times with complete certainty. This can happen due to inbound trucks facing disruptions from various factors such as congested traffic, inclement weather and vehicular breakdowns, resulting in late arrivals at the cross-dock. Therefore, Chapter 3 uses a Multi-Stage Stochastic formulation to create robust schedules which are least likely to be affected by such disruptions. An alternative method known as Progressive Hedging (PH) is also used to reduce the time taken to solve the cross-dock problem.

The final chapter introduces scheduling at intermodal cross-docks (IMCD) where freight by rail is transferred to trucks. Intermodal cross-docks further enhance supply chains by facilitating the use of cheaper and more environmentally friendly rail transport. To accurately represent reallife cross-docks, the assumption of sufficient storage space from the previous two chapters is now removed. Therefore, the IMCD problem now considers a finite storage space which is limited by the size of cross-dock. Numerical experiments show the impact of delays by the size of cross-dock and support the design-based decision-making of the number of doors a cross-dock should have.

Author ORCID Identifier

0009-0006-4564-8486

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