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48 Truck Drayage Productivity Guide the number of factors that affect dray turn time, a simple average is of little use. A more accurate and insightful analysis requires identifying the variability in queue times and the reasons for that variability, which, in turn, requires a distribution rather than an average. Driver/Truck Arrivals The number of drivers and trucks arriving during a given time period varies with the volume of work to be done and the choices made by drivers, customers, and dispatchers. As long as vessel arrivals and departures and customer shipping and receiving practices result in peaking, it is prob- ably impossible to eliminate queuing congestion and delays completely. The arrivals at the gate vary by day of week. At one terminal, sample data show Friday to be the busiest (Figure 61). Other port and terminal data generally show heavier activity toward the begin- ning of the week, or show different distributions with more extreme peaking. These day-of-week variations should be predictable and accommodated. The pattern of arrivals over the week depends on vessel schedules and customer choices. Customers are notified when vessels arrive and their import containers are unloaded. They, in turn, notify the drayage driver and typically want the import boxes quickly, often on the same day as unloading. The rush to get newly unloaded import containers accounts for peak queues on vessel arrival days. Similarly, there is an export peak as ves- sel departure day approaches, and exporters work to get their outbound containers to the marine terminal before the vessel cutoff time. Figure 62 shows hourly arrival patterns at Bayport, Port of Houston, for July 2009. The peak days were Tuesdays, with the peak hours being in the middle of the morning. Consistent daily peaking is also typically observed. It is common to observe long queues before the gates open in the morning and during lunch and coffee breaks. Since both drayage firms and their drivers are usually paid by the move, they have an incentive to make as many moves as pos- sible as soon as possible. A driver who starts early has a better opportunity to make more moves and earn more revenue than a driver who is less aggressive. Long-distance drivers arriving in the port area in the middle of the night often prefer to wait overnight in the marine terminal queue area so they can continue their trip as early as possible the next day. Sample 2007 Day of Week Entrance Gate Distribution 120,000 100,000 Annual Inbound Moves 80,000 60,000 40,000 20,000 0 Monday Tuesday Wednesday Thursday Friday Figure 61. Day-of-week gate arrivals--sample terminal data.