## 1 Introduction  
### Current Situation of Urban Logistics Enterprises
With the gradual improvement of modern logistics network, there are more and more categories of logistics distribution, from letters, daily necessities, and electronic products to large commodities such as home appliances and homes. The shape and weight of logistics packages change, and urban logistics enterprises mainly divide them into bulky parcels and standard parcels. Oversized parcels, also known as weighed parcels, refer to parcels whose weight or volume exceeds a certain threshold. Typical oversized parcels include e-commerce bulky items such as home appliances and home furnishing for end consumers, replenishment bulky items for various offline physical stores, and moving bulky items for relocated groups. At present, there is no uniform standard for the threshold of large parcels in the industry, and there are differences between different companies. For example, express companies such as Deppon and ANE have lower thresholds, such as the Deppon threshold of 3 kg and the ANE logistics threshold of 5 kg. However, express delivery companies such as ZTO, SF Express, and YTO have higher thresholds, such as ZTO Express with a threshold of 10 kg, SF Express with a heavy parcel threshold of 20 kg, and YTO E-commerce with a threshold of 30 kg. Bulky parcel threshold settings affect urban logistics site selection and route planning.  
A typical urban logistics network includes urban distribution centers, urban transit centers, and end-of-line demand points close to customers. Generally speaking, for standard packages, the specifications and standards include small weight and volume, low wear rate, and low requirements for sorting facilities, handling tools and logistics sites. However, the volume or weight of large parcels is large and the packaging shape is irregular, the parcel value is high, it is easy to wear, and the requirements for sorting facilities, handling tools, and logistics sites are high. As a result, there are significant differences between bulky parcel transit centers and standard express parcel transit centers in terms of capacity configuration, sorting facilities, and handling loading and unloading tools. The location of bulky and standard parcel transit centers also affects urban logistics site selection and route planning.  
At present, logistics enterprises mainly adopt the independent distribution mode of sub-network for standard parcels and bulky parcels, with low resource utilization and high distribution costs, and multi-type parcel collaborative distribution is an effective strategy for integrated logistics enterprises to solve urban distribution. Collaborative distribution refers to the centralized dispatch of logistics resources such as logistics facilities, transit centers, terminal outlets, distribution vehicles, and front-line employees to meet the collection and delivery needs of various types of logistics parcels. According to the demand characteristics of various packages, joint optimization of large parcel threshold setting, transit center location selection, and terminal demand point allocation (transit center coverage) is the key to implementing coordinated distribution.