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36 Truck Drayage Productivity Guide The problem descriptions are relatively generic, and are discussed in detail in relevant sections of this guidebook. Although the potential for delay and unreliability exists at rail intermodal terminals, off-terminal container depots, and shipper/receiver locations, those sources of delay were considered relatively minor. They could, however, have local or short- term significance. Marine container terminal turn time is the principle focus. The matrix shows it as an overall problem, and then provides separate entries for the six turn time components listed in Table 41. The problems covered have both time and reliability dimensions, which can be equally important. The problems are interrelated in complex ways. Taking chassis pools out of marine terminals, for example, will reduce associated delays, but may entail extra trips to position chassis outside the terminal. It is, therefore, more useful and accurate to view the matrix as a system rather than as a checklist of independent issues. Causes The causes section of the table is broken into two sections: "proximate" and "root." The proxi- mate cause may be thought of as the manifestation of the root cause. For example, long queue times is the symptom of a root problem such as peaking, legacy facilities, or poorly trained clerks. The distinction follows conventions commonly used in process improvement efforts, and has been adopted for that reason. Many of the proximate causes of delay, such as long gate queues or con- gestion at chassis yards, are immediately obvious, but the root causes are not. Moreover, some proximate causes, such as slow average gate processing times, may have multiple contributing root causes such as legacy systems, meal breaks, or inability to divert exceptions to a trouble window. A substantial part of the project effort was devoted to linking proximate and root causes, and under- standing the root causes. There are also root causes--such as peaking, communications shortfalls, and human error-- that contribute to multiple problems. That is not surprising considering the interrelated nature of the system. For those structural factors that are an inherent part of containerized shipping, such as peaking, the matrix suggests that some problems will persist and can be reduced but not eliminated. Human error can likewise be reduced through training or better information, but cannot be elim- inated. The matrix also suggests, however, that efforts directed at better communications, systems improvement, training, and other common issues will have multiple payoffs. Impacts The impacts section of the table categorizes the problems based on their adverse impact on drayage time, direct economic cost, emissions, and service quality. All the impacts are rough esti- mates for the purpose of showing order-of-magnitude results. The time impacts shown range from a few minutes per move due to gate processing delays, to an average of about an hour per move for trouble tickets or comparable exceptions. Since drayage costs are primarily a function of time, the time impacts drive the cost estimates. The most dramatic impacts are those associated with the "tails" of the turn time or gate time distributions--the 5% of transactions that take much longer than average. There have always been anecdotal reports of multi-hour turn times or queue times, but they have not been previously quantified. Service impacts are estimated based on the magnitude or the variability in process times introduced by the particular problem or issue.