III. LOCK CAPACITY 21 The purpose of this chapter is to review the controversy over timates of the capacity of the existing facility at Locks and Dam 26. e general nature of the controversy is that critics of the Corps have aimed that their capacity estimates are too low. The question of the pacity of the existing facility is very relevant in two ways. Other ings being equal, the greater the capacity of the existing facility, the re time is available for consideration of the decision as to how large should be. Also, the greater the capacity of the existing facility, the ss the impact on rail revenues over the next 10-20 years of increasing is size. The principal participants in the discussion have been, on the one side, le Corps and its consultant, Peat, Marwick, Mitchell & Company (PMM), and, the other side, Dr. Joseph Carroll of Pennsylvania State University 10 was engaged by the Western Railway Association to review the Corps' apacity estimates. stimation of Lock Capacity Generally speaking, it is best to express capacity estimates in a range, s there are many complex variables involved. It is important to bear in ind that the real question here is not of physical capacity but one of conomic capacity. Physical capacity represents the tonnage that could be ocked through if all tows were optimal size and all barges and all tows were ully loaded and all tows arrived on an optimal schedule. In the real world, f course, such conditions are not obtained. Many factors influence tow izes, the number of empty barges in a tow, and the times at which tows arrive t the lock. The economic capacity of a lock is approached when congestion eaches a point such that delays become a significant factor for some shippers, and traffic, as a result, are switched away from the river. It is clear hat these conditions will begin to obtain short of actual physical capacity ind that one should be talking about a range or zone of tonnage in which lelay costs become significant. The Corps has estimated the capacity of the present facility at 73 million tons. The PMM has used the figure of 77 million tons, and Dr. Carroll has used a range of 80-90 million tons. Lock capacity in this sense is determined by multiplying the number of commercial tows which can be processed during a given time period by the average tonnage,per tow. Five underlying factors common to all lock capacity estimates are: - - Lock Utilization Rate--the fraction of time the lock Average time required to lock through a commercial tow. Appendix A provides a fuller description of the general methodology of lock capacity. 22 - - Average number of tons per loaded barge. Average number of barges (loaded and unloaded) per tow. Fraction of barges processed through locks that are loaded. Corps Methodology The Corps' approach to capacity determination is outlined in Appendix S of Design Memorandum 11. A computer simulation model is used which is based on movements of tows up and down the reach of the Mississippi River. Model inputs include projected and historical commodity flows and assumed probati distributions for selected variables such as barges per tow and the operating times for various lock activities (tow approach time, chamber filling time. etc.). For the base case, these distributions are chosen so that if historic commodity flows are used as inputs, resulting values are consistent with historical data. Assumed lock operating times are those which were found to exist in experiments made in connection with the PMM study of operational procedures. The model outputs include a measure of lock utilization and total tow delays at Locks and Dam 26. By varying commodity demand and holding all else constant, a relationship can be found between tonnage throughput and lock utilization. A utilization rate of 98 percent is used in the resulting equation and the corresponding tonnage throughput is offered as a point estimate of economic capacity. The Corps developed lock capacities based on several different sets of assumptions. The most important are: 73.0 million tons --Assumes 1972 tow size, improved operational 78.8 million tons --Larger tow size and improved operating Peat, Marwick, Mitchell & Company In July 1975, PMM completed a study for the Corps of Engineers whose main focus was an evaluation of operational improvement at Locks and Dar 26. PMM used historical data and operational times determined from experiments conducted at Locks and Dam 26 incorporating several different procedural improvements. By assuming a lock utilization rate of .98 for the main chamber and .75 for the auxiliary, the capacity for the most efficient procedures was estimated to be 77 million tons. In providing their estimate, PMM suggests that some additional time savings in lock operation may be possible by adopting additional operational procedures. 233 iticism of Corps' Procedures Dr. Carrol estimated that the capacity of the present facility was ound 80-90 million tons annually based on an appraisal of the work ne by the Corps. He has concluded that the Corps' estimates of locking mes is too high, that too high a time penalty was being imposed for e of the 360-foot lock and that the tow sizes and operating procedures used the Corps should be changed. Following is a discussion of some of Carroll's generalized criticisms of the Corps' estimates followed, turn, by a detailed discussion of his specific criticisms. General criticisms include: The Corps has provided several different estimates of - Lack of an analysis of the entire system. - Lack of data on commodity mix in the traffic. In evaluating the importance of the first point, it should be remembered hat lock capacity at any point in time is based on existing technology and rends in average tons per barge. Early Corps estimates, for example, did ot include non-structural operational improvements such as switch boats. Analysis of the whole system is more important in benefit evaluation han it is in evaluating the capacity of an existing lock. Mix of commodities will affect tow size, i.e., petroleum tows tend to e smaller than grain tows. The overall impact of commodity mix in the resent case appears much less important, however, than other capacity variables. Dr. Carroll's general criticisms thus appear more relevant to other areas of the decision-making process than to lock capacity analysis. Use of Auxiliary Lock Because many of the tows on the river exceed the length of the current locks at Locks and Dam 26 or arrive with their barges in the wrong configuration, double locking, setover and knockout lockages are required.2/ This is particularly prevelant in the case of the 360-foot lock in the present facility. Understandably, many tow boat operators prefer to incur some delay to go through the 600-foot lock rather than double lock through the smaller 360-foot 21 A double lockage occurs when all the barges of a tow cannot fit through the lock in one lockage. Setovers occur when the tow is not in the right configuration to go through the lock in a single lockage and must re-configure to get through. A knockout is similar to a setover, but only the towboat needs to be arranged for lockage. 24 lock. The Corps' model includes "penalty times" to account for the reluctance to use the auxiliary chamber; five-hour waiting penalties are assessed. Ir the model, when such tows arrive at the locks, they have an option as to which chamber they use. A tow makes this choice by considering the total delay it would incur under the two options and choosing the chamber which minimizes delay. With the penalty times, a tow could approach locks where use of the main chamber involved a four-hour delay while the auxiliary (360-fact chamber was empty. Tows requiring double, setover or triple lockages ir the auxiliary would choose to use the main chamber, since they would "perceive a waiting penalty in excess of four hours for the smaller chamber. The use of penalty times is a device to make the model conform to certain observed realities at Locks and Dam 26, where tows have shown a tolerance of small delays associated with use of the main chamber in preference to lockage through the auxiliary. The device leads, in the view of some critics, to an under-utilization of the auxiliary chamber at high levels of total utilization (and hence to an understatement of capacity). The Corps' response is that, for high tonnage simulations, utilization of the smaller chamber is 98 percent, but that their model may overstate delays at lower tonnages by under-utilizing the auxiliary chamber. At high rates of utilization, delays per tow exceed the penalty times assigned so that a high percent utilization of the smaller chamber in these situations is a likely result, as the Corps states.3/ Improved Operational Procedures Peat, Marwick, Mitchell & Company have suggested additional improvements in operational procedures beyond those tested in their study, which could lead to further reductions in lock operating times. These improvements include: The impact of implementing these suggestions is not known, and PMM is somewhat ambiguous on this question. 3/ Compare- While the reductions in tow processing time achieved See Corps Table B5 of Appendix G of Design Memorandum 11. ith- small. .the cumulative effect of implementing many of these alternatives could be significant.4/ If several of these additional improvements were operating improvements already tested), although they will probably not be of the same magnitude. The reduction in operating times resulting from the experiments of MM which involved the use of switchboats are listed in Table III-1, long with percentage of lockage types. These are clearly substantial Denefits. Any attempt to guess at the impact of adopting further operational improvements would be speculative. Seasonal Adjustments The Corps' model simulated one month of waterway traffic and extrapolated yearly tonnage throughout by multiplying the monthly total by roughly 10.5. This reflects the fact that 1/10.5 or 9.5 percent of the traffic currently moves through Locks and Dam 26 during the busiest month (the assumed month for the simulation). As traffic levels increase, it is reasonable to assume that this percentage would decrease leading to a larger multiplicative factor (and hence to greater capacity). The logical upper limit to the factor would be 365/30 = 12.2. There are, however, economic and technological reasons to support a lower number. The current traffic pattern reflects the existing response to conditions of demand and supply for water transportation. Supply is dependent to a large degree on costs which include existing delays. Increased delay costs must be weighed by the shipper against the costs of waiting to ship (storage costs, etc.). In addition, the Upper Mississippi is closed by ice during the winter months. Tow Size The primary capacity estimates of 73.0 million tons (Corps) and 77.0 million tons (PMM) both assume tow sizes (tons per tow) roughly equal to the "current" (1972) tow size. Average tons per tow have been increasing since World War II and have continued to increase in the period since the Corps' estimates were made (1972-1975). Capacity estimates must be carefully examined in light of this fact.6/ 4/PMM Study, page VI-11. 5/PMM Study, page VIII-11. 6/Note that a larger average tow size means there will be an increase in the percent of complex lockages that occur (and hence longer average locking time). |