Three basic types of movements occur in every form of land transportation: Longitudinal, lateral, and vertical. The well-type stackcar reduces the force in each direction, which minimizes the associated movements, especially compared with conventional intermodal flatcars and trucks.

Longitudinal movement (commonly referred to as slack action) occurs during the operation of the train as speed is increased or decreased. In most instances, Pacer Stacktrain operates solid stacktrains that remain intact from origin to destination, which avoids the need to switch. Slack action can occur because of the "run-in" and "run-out" of a train in transit. This run-in/run-out movement is created by the 15 inches of cushioning, or play, in each coupler on both ends of a conventional intermodal flatcar. When trains are going uphill, this cushioning extends to its full 15 inches. However, when the trains are going downhill, they contract until nearly all of this extension is gone. The movement also occurs when the train is slowed by braking the locomotives only (called dynamic braking), instead of using the air brakes on each flatcar.

Since the normal size of a standard intermodal train is approximately 50 to 60 flatcars, it is theoretically possible to experience 125 to 150 feet of combined slack action whenever the coupler cushioning goes from the fully extended to the fully contracted position throughout the train.

The stackcars used by Pacer are designed with a fixed, semi-permanent attachment (referred to as an articulated connection) between each of the platforms, instead of the conventional coupler found on most flatcars. The rigid nature of this articulated connection completely eliminates the slack action at these points. Only the ends of each stackcar have conventional couplers. Thus, a stacktrain approximately the same length as a standard intermodal train would have 10 to 13 stackcars and a theoretical maximum movement, caused by slack action, of 25 to 33 feet. This means that Pacer Stacktrain rail cars eliminate 80 percent of slack action while they can carry 50 percent more freight on the same size train.

To further minimize the potential damage to freight from slack action, the 15 inches of cushioning movement in each coupler has been dampened. This makes the coupler cushioning much stiffer during the run-in/run-out movements and reduces it to a slower, more controlled form of slack action. This controlled slack action eliminates the jarring effect at the end of the coupler travel that causes most in-transit damage problems.

Lateral movement (sway or roll) is common in rail transportation because of the variation in height from one side of the track to the other side. Every rail (as well as highway) service has a natural amount of sway that takes place in transit. The exaggeration of this lateral motion by the suspension system (springs) of a trailer does not occur with a container on a stackcar.

The Pacer Stacktrain stackcars use articulated connectors that join the intermediate ends of the platforms, which significantly reduces this rolling movement. As one platform rolls in one direction, the next one is rolling in the opposite direction. As a result, the platform movements counteract each other, dampening and minimizing the rolling effect. This is true under all types of loading conditions, even in the most severe case when adjacent platforms have widely varying centers of gravity. The well-type design of the Pacer Stacktrain stackcars provides the lowest possible center of gravity because the bottom container is less than 12 inches above the rails. This minimizes the rolling tendency of the platform and is the primary reason for the stackcar's stability.

Vertical movement (bounce or vibration) in rail service is caused by the distance between the "truck centers" (wheel assemblies) of each car. The greater the distance, the greater the possible movement. Conventional flatcars have approximately 80 feet between their truck centers, while the Pacer Stacktrain stackcars have only 50 to 58 feet. This feature, combined with the reduced camber in the platform construction, minimizes the vertical accelerations while the units are in motion. When these design features are coupled with the fact that a steel wheel rolling along a continuously welded steel track is the smoothest form of surface transportation, it's no wonder that vertical movement is virtually nonexistent in a stacktrain ride.

The exceptional ride quality of our service has made possible a new standard of dependable, low-risk transportation for domestic shippers. The Pacer Stacktrain "smooth move" is made possible by efficient stacktrain technology.

The five-platform articulated well-car produces the best in-transit ride of all competing transportation modes. The maximum benefit from this technology is achieved when containers are moving in a "dedicated" stacktrain environment. These dedicated trains are made up exclusively of stackcars usually destined to a single location, which eliminates the need for switching at intermediate terminals. The stackcar technology minimizes slack action and dramatically reduces the effects of any handling forces on these trains. Pacer Stacktrain transports the majority of its containers on dedicated stacktrains in dense traffic lanes between major markets. Containers moving in traffic lanes between secondary markets that have less traffic density may move in "Standard Service" on "mixed consist" trains. These trains are made up of multiple types of cars, which may include stackcars, spinecars, and flatcars in TOFC and COFC service. In some cases, such as when there is insufficient volume to load all wells in a stackcar, containers may be loaded to one of these other types of cars. These trains are subject to switching at intermediate terminals and the containers do not receive the full ride quality benefits of reduced slack or dynamic braking actions. These conditions change from time to time; please check with your Pacer Stacktrain customer support representative for up-to-date information.

The superior ride quality provided by dedicated Pacer Stacktrains means that our customers' freight is subjected to less stress during transport and therefore is less likely to incur damage. This does not mean that the need for appropriate blocking and bracing is eliminated. Compliance with Association of American Railroads (AAR) blocking and bracing requirements (and 49 CFR, Parts 100-179, for hazardous materials) is still required to protect against in-transit damage. For additional information, please see the section titled "Liability for Loss or Damage of Freight" in the Guidelines section of this directory.