Intermodal railcars come in various types and sizes. One of the smaller type of railcars is a 70-foot single well railcar, which holds one 40-foot or 45-foot container. A well is a square-shaped bowl in which a container is placed. Another type of railcar is a stack car that holds two 40-foot containers in a well, when they are stacked. Where a single well is one of the smallest railcars, a 325-foot five-well articulated railcar is one of the largest. An articulation is when two or more railcars share a single truck or set of axles, thereby making them inseparable and handled as a single railcar.

The total intermodal railcar capacity contains two areas of capacities: terminal and staging. The terminal maximum capacities in the intermodal study are based on historical utilization calculations. Since railcar lengths vary, not all the footage at the terminals can be utilized perfectly. For example, when there is room left on a track before a required break for a three well, but the next railcar in the train is a five well, the five well must go either after the break or be moved to the next track. This creates two capacity maximums: one "theoretical" maximum and one "real world" maximum. 

Based on the Port of Tacoma's 1:1 agreement with Tacoma Rail, there is one foot of staging track for every one foot of terminal track. If 1:1 at the terminals was completely used, Tacoma Rail would only have enough room for a couple run around tracks for intermodal staging. Tacoma Rail uses these to get from one side of the staging yards to the other. Tacoma Rail can't do any major switching operations in this instance. However, as volumes increase, the amount of pure trains (all cars destined to one terminal) can increase. Pure trains minimize the amount of switching needed. Refer to the track usage page for additional clarification on railroad switching needs and requirements. The staging utilization number includes both inbound (westbound) and outbound (eastbound) traffic. This measures the entire impact each terminal has on the Tideflats staging infrastructure.