Allisions, Collisions and Groundings: Estimating the Impact of the Physical Oceanographic Real Time System (PORTS(R)) on Accident Reduction

Reductions in the rates of domestic allisions, collisions and groundings (ACGs) are the result of technological advances as well as implementation of best practices in the maritime industry. This study estimates long-term gross benefits derived from expanded implementation of the National Oceanic and Atmospheric Administration’s Physical Oceanographic Real-Time System (PORTS®) with respect to reductions in ACG rates in the United States. Following PORTS® installations that provided expanded coverage of U.S. ports and adjoining areas, concomitant decreases in accident rates occurred. While previous estimates suggested that between twenty and sixty percent of grounding accident reductions were due to PORTS®, current research suggests that up to half of ACG rate reductions were due to such installations. Annual gross benefits resulting from lowered ACG rates at PORTS® locations installed through 2016 were estimated to approach $21 million. Over the estimated ten-year economic life of PORTS® instruments, present PORTS® installations could produce a present value saving of $180 million. If expanded to an additional 23 ports where economic justification might be made, up to $10 million could be saved. Over ten years this would equate to over $84 million. This research article is available in Journal of Ocean and Coastal Economics: https://cbe.miis.edu/joce/vol5/iss1/4


INTRODUCTION
One of the responsibilities of the National Oceanic and Atmospheric Administration's (NOAA) National Ocean Service (NOS) is to promote safe and efficient maritime navigation within the United States. NOS's Center for Operational Oceanographic Product and Services (CO-OPS) developed a public information acquisition and dissemination technology known as the Physical Oceanographic Real-Time System (PORTS ® ) with the Greater Tampa Bay Marine Advisory Council in 1990. PORTS ® are installed and managed in partnership between NOS and port management. 1 Edwing (2013) described PORTS ® as a collection of meteorological, oceanographic, and geographic instruments that are integrated into a system that provides accurate, reliable, real-time, quality-controlled information about the environment (observations and predictions) in which commercial mariners and recreational personnel operate. The number of and type of instruments installed are based on the need of the individual port or system of ports. For example, the Chesapeake Bay that contains 97 separate instruments 2 provides shared data for 10 ports. 3 The smallest single port PORTS ® installation consists of a single water-level gauge.
The purpose of this analysis was to investigate Allisions, Collisions and Groundings (ACGs) over a long period from several perspectives including number of occurrences, relative incidence rates, and costs associated with The Department of Commerce (DOC) reported in 2010 that over 69 percent of U.S. international trade (measured by tonnage) moves through the nation's ports and harbors and represents almost 41 percent of total international cargo value. 7 Although there are over 400 ports in the United States according to the DOC, only half reported handling imports and/or exports in 2016. 8 Highly concentrated, the top 60 locations handled over 98 percent of all cargo value and almost 96 percent of total cargo tonnage.
Between 2002 and 2015, total vessel calls at US ports increased from 50,877 to 82,044-a 48 percent increase. 9 At the same time, total deadweight tonnage increased from 2.6 billion to almost 4.2 billion-a 60 percent increase. Such larger vessels require deeper and wider channels that necessitate more frequent • "We use PORTS ® data on the Bayonne Bridge and nearby Bergen Point to bring in vessels within 2' of the bridge and 2' under keel clearance at the same time. If PORTS® sensors were shut down, there are 3-4 classes of vessels we will not be able to bring to the Port." Comment from a NY Harbor Pilot.
• The Final Report of the Delaware River and Bay Oil Spill Advisory Committee, published in December 16, 2010, highlighted the importance of PORTS ® to preventing maritime accidents and associated pollution releases. Recommendation 14 of that report was to "fund the upgrade, continued operation, and maintenance of PORTS ®" . That report indicates that PORTS ® has the potential to prevent shipping accidents and subsequent environmental damage and save millions of dollars in response, restoration, and damage claims. 12

CURRENT STUDY
The current study investigated only gross benefits from accident reductions for several reasons. First, NOAA only sets standards for PORTS ® sensors and related communication infrastructure. It does not sell such equipment to ports and consequently does not know their acquisition costs. Second, obtaining installation, operating, and maintenance costs would be extremely difficult from current users and speculative at best for potential users. This is due to the variety of vendors and the number and type of sensors employed at current locations and the unknown needs of future potential PORTS ® users. 13 Finally, costs of subsequent modification of PORTS ® systems would also be difficult to identify.
The study was conducted and presented in such a way as to be conservative in stating gross benefits, and transparent to enable the reader to evaluate the estimated gross benefits of PORTS ® for themselves and develop alternative allocations of gross benefits should additional data become available.
At the end of 2016, PORTS ® had been installed at 77 major port locations. 14 International vessel traffic at these locations represented almost 87 percent of total 12 Pages 37-38. 13 Local port partners determine how many sensors and where those sensors will be located and is responsible for purchase, installation, and maintenance of its system. 14 About 200 ports are identified each year as import and/or export locations by the U.S. Department of Commerce's, Bureau of the Census' USA Trade Online database. Of the 60 locations without PORTS ® , only about one-third of these estimated to be large enough in terms of vessel transits and historical accident rates to potentially warrant PORTS ® installations. (Refer to  Table 10.) 6 waterborne cargo value and over 81 percent of total cargo weight. As PORTS ® have been largely installed at the largest container handling facilities; it covers over 91 percent of cargo value handled in containers and almost 89 percent of total container weight handled at such locations. Among the remaining port locations with a PORTS® installation, the largest 60 locations (in terms of tonnage) were reviewed to estimate potential gross benefits that PORTS ® might be capable of generating. 15 During the study period, a number of technological and management and human factors have contributed to reductions in the number and severity of marine accidents (e.g., increased use of the Automated Identification System, electronic charting, safety management systems, bridge resource management and crew endurance/anti-fatigue programs, etc.) Reductions in accident rates attributed to installations of PORTS ® were based on multiyear analysis of marine accident data amidst these other improvements.

PREVIOUS RESEARCH
A number of earlier studies by Kite-Powell (2005, 2007, 2010 estimated the gross economic impacts of PORTS ® at specific locations including Tampa Bay, Houston/Galveston, and Portland. Later Wolfe (2016) estimated gross economic benefits from the then 58 existing PORTS ® installations as well as estimated the potential value that might be realized from expanded implementation to an additional 117 ports. Both Kite-Powell and Wolfe detailed gross benefit estimates derived from a number of sources with associated varying degrees of confidence. Benefits were envisioned to result from: (1) increased vessel draft and cargo loadings; (2) reduced delays among commercial vessels; (3) improved (petroleum) spill pollution response; (4) avoiding ACGs; (5) reduced distress cases; (6) improved weather forecasts; (7) improved storm surge forecasts; (8) enhanced recreational boating, fishing, and beach recreation.
In a series of multi-year analyses, Kite-Powell estimated that reductions in groundings resulting from PORTS ® installations ranged from 20 to 60 percent depending on the type of vessel and location: • "A plausible range for the decrease in grounding risk for Tampa-Bay selfpropelled ship transits attributable to PORTS ® data is from 20 to 50% from the long-term baseline level of about 1.5 groundings per 1,000 transits" (Kite-Powell, 2005 • "While it is not possible to assign a specific effect to a specific cause with certainty in this case, it is plausible that LOADMAX 18 /PORTS ® may contribute 25 to 50% of this reduction in grounding risk" (Kite-Powell, 2010). 19 In working with data from 2010, Wolfe (2016) observed the rate of allisions at locations with PORTS ® was 67 percent lower compared with locations without PORTS ® . Collisions and groundings at PORTS ® installations were seen to be 45 and 80 percent lower, respectively, than at locations without PORTS ® facilities.

8
The DOC's, U.S. Census Bureau's Foreign Trade Division, USA Trade Online is the official source of import and export statistics carried by waterborne vessels and air. DOC also summarizes traffic from these 400 locations into 48 district totals. Beyond facilities alone, the database provides current and cumulative U.S. export and import data on up to 17,000 commodities by U.S. trading partner defined under the International Harmonized System Code (HS) 20 and the North American Industry Classification System NAICS) 21 codes, at the 10 and 6-digit levels of granularity, respectively. 22 Data over the range of availability at the time of this report (2003 to 2016) was selected to identify dominant import and export port facilities. Selection of the period allowed for variations in transportation activity that occur during at least one complete business cycle to be observed. 23 While meant to identify major import and export locations as well as to estimate coverage of PORTS ® , USA Trade Online must be viewed with some caveats as to the precise level of tonnage and/or cargo value attributed to a specific port may have been disguised or redacted in some manner to ensure confidentiality.
There are several ways, especially when employed with other publically available data, that a specific shipper or receiver might be identified owing to the unique nature of the goods being shipped and/or received. In those cases, traffic levels (e.g., tonnage and/or cargo value) may not be reported accurately in USA Trade Online for a given port. 24 To conceal data, traffic at the restricted location 20 The U.S. International Trade Commission maintains the Harmonized Tariff Schedule of the U.S. covering international traffic. 21 The NAICS was developed by the Office of Management and Budget in 1997 to classify business establishments for the purpose of collecting, analyzing and publishing statistical data on the U.S. economy. 22 The statistics include both government and non-government shipments by vessel into and out of the U.S. foreign trade zones, the 50 states, District of Columbia, and Puerto Rico. The statistics exclude postal and military shipments. 23 The last recession ran from December 2007 to June 2009. The National Bureau of Economic Research (NBER) is considered the authority that identifies a recession and which takes into account several measures in addition to GDP growth before making an assessment. 24 There also may be ports of notable activity that are not referenced because they do not directly send or receive international traffic. Other ports showing no traffic may be listed but are unmanned, are of a vestigial nature or while decommissioned remain on the list. may be added to the traffic reported at the largest port within the port's district assignment.
Finally, this database does not record the number of total vessel transits that occur by port that is essential to investigate the relative rate of marine accidents over time. Even so, to identify major international ports USA Trade Online contains the best data on import and export traffic that is publically available and its restrictions do not significantly impede the overall goal of identifying major US ports.

United States Coast Guard
The Marine Information for Safety and Law Enforcement (MISLE) system contains data related to commercial marine casualty investigations reportable under 46 C.F.R. 4.03 and pollution investigations reportable under 33 C.F. R. 153.203. 25 The data reflect information collected by U.S. Coast Guard (USCG) personnel concerning vessel and waterfront facility accidents and marine pollution incidents throughout the United States and its territories. Collisions are defined as the striking of a (moving) object upon another (moving) vessel. Allisions describe the striking of a moving vessel with a stationary object (pier, docked or anchored vessel, bridge, etc.) and groundings represent instances where a vessel collides with the seabed or side of the channel. 26

United States Army Corps of Engineers
The U.S. Army Corps of Engineers (USACE) is home to the Waterborne Commerce Statistics Center (WCSC), which collects, processes, and publishes marine vessel transit counts and cargo flow totals for ports, rivers, and navigable waterways throughout the country. This data is used by the Corps to inform decisions concerning new investments in port and waterway expansions as well as annual operations and maintenance of existing water resources infrastructure. By using the proprietary, dock-level origin-destination cargo flow data maintained by WCSC within a routable network of georeferenced channel segments, the Channel Portfolio Tool (CPT; Mitchell 2009, Kress 2016 allows for the entire inventory of USACE-maintained federal navigation projects to be analyzed, sorted, and summarized per user-defined criteria. 27 CPT conducts nearest-neighbor matching of WCSC's Master Docks database with a spatial network representing USACE-maintained channels and waterways. The cumulative statistics for tons, dollar value, vessel draft, commodity types, and traffic types are then compiled for each individual reach (channel segment) in the network. 28 CPT has been employed in several previous analyses, notably a recent gross benefit assessment of the CO-OPS' PORTS ® (Wolfe 2016). The origindestination cargo flow data that is readily available via CPT has been used as the objective function basis in several waterway and freight network optimization studies , Khodakarami 2013, Kruse 2014, all of which consider the interdependencies that arise among portions of a transportation network with cargo flows that are shared across many segments. Other efforts (Rosati 2013, Dunkin 2015 have focused on quantifying the relative economic impacts to shipping interests as a result of channel shoaling and vessel draft restrictions. Internal to the USACE, CPT has been used within the annual maintenance dredging budget development cycle to generate channel throughput metrics that focus on just the cargo utilizing the five deepest feet of maintained depth (GAO 2017), since all else being equal, this is the cargo most vulnerable to year-to-year channel shoaling. Annualized throughput totals are shown in terms of cargo tonnage (short tons), cargo value (U.S. dollars), and vessel trip counts. 29 The data 27 Special thanks is extended to Dr. Marin M. Kress (Research Physical Scientist, U.S. Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory) who was instrumental in provision of CPT data. 28 CPT output can be selected from a large number of options to enable the researcher to focus on specific aspects of vessel and commodity movements Present channel conditions and historical shoaling rates are compared to the draft profile to determine the amount of cargo that is directly impacted by channel shoaling conditions. 29 The Department of the Census supplies cargo value to the USACE. Under the January 2015 Memorandum of Understanding between the two agencies, cargo value cannot be made available to users outside of the USACE owing to data confidentiality concerns. Hence, cargo value in this study was obtained from the USA Trade Online database. is collated into a nested hierarchy that reflects the organizational structure of the Corps' Civil Works mission area: at the most granular level, navigation projects in CPT are divided into "reaches," which can represent individual berthing terminals within a port, or longer portions of channel that are maintained to consistent dimensions and for which the cargo throughput totals will be relatively stable (pending the distribution of any landside dock facilities). These channel reaches make up the spatial extent of federally authorized Navigation Projects, the next level within the CPT hierarchy and which the Corps of Engineers maintains to dimensions specified in Congressional legislation.
Commodity classifications are similarly organized within CPT, featuring a nested coding convention that ranges from 1-digit specificity (10 resulting cargo types) to a five-digit commodity code level with over 660 commodity types. 30 Per its Navigation mission in support of maritime commerce, the USACE actively maintains dredged channels in over 360 individual nationwide projects that are detailed across more than 970 areas or river segments. 31 While CPT does not provide origin or destination data involving specific vessel transits, that does not affect the value of the database as it is unique in its ability to identify the number of both international and domestic vessel transits at highly specific geographic levels.

MARINE ACCIDENT OVERVIEW
In order to place ACGs in perspective, it is prudent to establish the larger picture in which ACGs are reported. During the 2003 to 2016 period over 136,000 incidents were reported to the MISLE database across 122 categories. 32 During 30 The commodity code structure developed by WCSC is unique to the USACE and generally reflects the types of bulk commodities that are commonly encountered in waterborne transportation. Crosswalk tables are available to link the WCSC codes to other conventions such as the Harmonized System (HS) Commodity Code system. The USACE stores its commodity code data to five digits. While not as detailed as the Census Bureau's seven-digit commodity data, the CPT data is detailed enough for nearly all marine transportation research. 31 Within CPT, a number of port locations are identified as "non-project," which refers to ports and waterways that are not federally authorized navigation projects. This does not mean that cargo cannot move there, just that the USACE has no authority or obligation to maintain those areas. 32 Among the 122 MISLE categories were: abandoned/derelict, adrift (unmanned), alleged violation of law/regulation, anchored [unmanned], assist other agency, beset by weather, boating the 2003 to 2004 period of time, anecdotal evidence suggests that "no consequence" incidents including "touch and go" groundings and "bump and go" allisions that did not result in any damages were not uniformly reported.  (Figures 2 and 3). Consequently, research was focused on more complete data beginning in 2005. Overall, ACGs have been relatively rare events, occurring in little more than 0.05 percent of total vessel transits between 2008 and 2015. 34 Since 2011, there has been a general decline in reported ACGs ( Figure 4). Overall, collisions result in much higher rates of mortality and vie with allisions as a major causal agent in morbidity (Table 1)

PORT AND PORTS ® IDENTIFICATION
During the 2003 to 2015 period, over 200 port locations imported and/or exported vessel traffic. 36 Of these, 77 locations, or about 31 percent of the total, had PORTS ® installations in 2016 or before. A list of these locations is provided in Appendix A. Remaining locations without PORTS ® are listed in Appendix B.

Matching ACGs with Locations with and without PORTS®
Where PORTS ® had been installed, MISLE accidents were matched with an individual port location based on the area of surveillance or "influence" provided by PORTS ® navigational aids. This was done through a "lassoing technique" based on the expertise of PORTS ® managers. 37 In cases where PORTS® had not been installed by the end of 2015, not knowing the locations or numbers of PORTS ® sensory instruments which might be installed in the future, a series of three, five, and ten mile radii were drawn around these locations to estimate potential areas of influence if PORTS ® were to be installed. During the assignment process, extreme care was exercised to prevent duplicative assignment of ACGs between existing areas with PORTS ® and adjacent locations owing to overlapping radii with existing PORTS ® ' area of influence.
For example, accidents that had already been assigned to an existing PORTS ® location (Tacoma, WA in the lower portion of Figure 5) were removed 36 Note that import and export traffic was not transported through all 240 ports identified in USA Trade Online in each of the years from 2003 to 2015. The 13-year survey period was employed to assess long-term activity at these locations. For example, in 2016 the number of ports, which handled import and export goods, fell to 216. Some of this reduction in port count may have been due to mergers of one port's data with another owing to confidentiality concerns. The extent to which this may have occurred is not known. 37 Special thanks to Darren Wright (Program Manager, Maritime Services, Center for Operational Oceanographic Products and Services, National Ocean Service, National Oceanic and Atmospheric Administration) for his assistance in identifying areas of PORTS® influence as well as Percy Pacheco (Environmental Engineer, Office of Coast Survey, National Ocean Service, National Oceanic and Atmospheric Administration) for his GIS support. from the radii of a potential PORTS ® location (Seattle, WA in the upper right portion of the figure).

Figure 5
As several of the locations without PORTS ® were within three, five, or ten miles of one another, and it was impossible to know when and if these sites without PORTS® may receive them or the extent of those installations, overlaps of potential areas of influence among these potential sites were allowed to remain. 38 This resulted in a different manner in which the results of potential future benefits could be estimated. In this case, an initial ranking of locations without PORTS ® was made employing the individual location's potential contribution to future benefits. It is fully understood that these estimates cannot be 38 For example, in the port of Savanah, GA, a water level gauge with meteorological instrumentation (e.g., wind speed and direction, barometric pressure, air temperature, etc.) is located at Fort Pulaski while an air gap sensor is located more than 13 miles up-river at the Talmadge  summed to estimate a grand totalrather employed to provide an initial ordinal ranking of potential locations for future PORTS ® installations. 39

ANALTICAL APPROACH
Three approaches were employed to estimate the impact of PORTS ® on ACG rates, which are estimated based on the maritime casualty event counts in the MISLE database and the vessel transit counts obtained from the Corps' Waterborne Commerce data via the CPT. The first was based on a direct comparison of ACG rates before and after PORTS ® installation at the same location. The second was predicated on a brief span of time when a large number of PORTS ® were installed. The final estimation compared beginning and ending years of the study (2008 with 2015) ACG rates at locations with and without PORTS ® .

Direct Location Comparison
Ideally, ACG rates would be compared for several years before and after a PORTS ® installation to estimate the impact of such changes. The use of several years of data could help overcome experiences in an atypical year. Absent documentation of major changes among all other types of navigational aids, it was assumed that the documented installation of PORTS ® represented the most significant documentable change among ACG reduction agents.
Seven port locations had been installed which provided a sufficient number of "before" and "after" ACG events (Table 2). If PORTS ® had been installed in November 2010, all ACGs and vessel counts for 2010 would be assigned to the "without (PORTS ® )" period. ACGs and vessel counts for 2011 and later would be assigned to the "with (PORTS ® )" group. As this approach reduces some of the benefits of PORTS ® through assignment of ACG events that occurred within the partial year of PORT ® installations (e.g., transfers to the "without" group), it is likely that this methodology will result in a conservative estimate of gross PORTS ® benefits. 39 In the partnership between a port authority and NOAA, the determinations for future PORTS ® locations can be based on the goals improving personal safety, preservation of property, and enhanced environmental protection. PORTS ® investments can result in different levels of improvement at varying locations based on the types of ACGs that are prone to occur there and the types of cargo handled.  Ultimately, only seven of all PORTS ® locations could be compared on a full year's basis at least three years before and after installation (Table 2). Among these seven locations reviewed in this manner, evidence suggests reductions among all types of ACGs occurred once PORTS ® had been installed (Table 3). In these instances, PORTS ® appeared to have differential impacts on ACG reductions --most effective in collisions and allisions and to a lesser rate with groundings.

TYPE OF INCIDENT
Although at the low end of the range of Kite-Powell's (2010) earlier estimates, direct before and after comparison at these seven locations suggest at least a 20 percent reduction in groundings was due to PORTS ® . The drawback to this approach is the number of locations and the level of traffic these seven port locations serve as these places represent less than ten percent of all locations with PORTS ® and little more than two percent of all vessel transits during the 2008 to 2015 study period.

Major PORTS ® Installation Period
A second approach to estimate the portion of ACG reductions due to PORTS ® installations was made involving changes in ACG rates which occurred   The extent to which other navigational aids were enhanced or more efficiently utilized at these locations is the underlying question in attributing ACG reductions to PORTS ® versus all other navigational aids. During the 2008 to 2010 timeframe, enhancements in all navigation aids (e.g., AIS data, electronic navigational charts) as well as improved knowledge and use of such technological supports undoubtedly took place alongside the expansion of the 17 additional PORTS ® installations. Enriched management and human factor training, including boosted safety management systems, greater bridge resource management, boosted crew endurance, and anti-fatigue programs, were certainly further refined and expanded. 43 However, without documentation to identify significant advances or increased utilization of other navigational aids and technological and managerial systems at these locations during the timeframes and where reductions in ACG rates occurred following PORTS ® installations, advances among these other navigational aids was deemed to be more evolutionary than revolutionary as compared with expanded use of PORTS ® . In other word, the addition of PORTS ® was seen as a dominate factor in ACG reductions.

Long Term Evaluation of ACG Changes
A third method to assess the impact of PORTS ® installations is a comparison between the first year (2008) and last year (2015) of the analysis. Employing the same ACG assignment methodology to "with" and "without" PORTS ® , a comparison between the first and last year vessel transit data was made to calculate changes in ACG rates (Table 4). Comparison of the base year (2008) with the last year transit count data was available (2015) suggested that the number of vessel transits that occurred at locations with PORTS ® per ACG event increased by almost 163 percent. At the same time, the number of vessel transits per ACG event that occurred at locations without PORTS ® declined by almost 31 percent. As this analysis did not measure the distance from shore of any of the ACGs which occurred outside the area of influence from a PORTS ® installation, the without PORTS ® figures cannot be directly interpreted as a potential measure 43 Critical skills include enhanced communication, teamwork, decision-making, and situational awareness. Refer to: https://www.marineinsight.com/guidelines/understanding-bridge-resourcemanagement-and-its-key-elements-on-board-ships/ of future ACG reductions should PORTS ® be universally installed. In some cases, the ACGs occurred at more than 10 miles from shore. Another way to present before and after results is calculation of the number of vessel transits that took place for each reported ACG (Figure 8). The number of vessel transits that occurred per grounding at a location with PORTS ® increased over 190 percent. Vessel transits per allision increased by almost 155 percent and transits per collision increased 141 percent at PORTS ® locations.

Value of Mortality Risk Reduction
In assessing the potential benefits associated with reductions in injuries and deaths resulting from AGGs, dollar values associated with these events must be calculated. In performing analysis of their programs, most Federal agencies have sought to identify these values through estimations of a Value of Statistical Life Year (VSLY). VSLY represents an approach to view the risks that people are voluntarily willing to take and how much they must be paid for taking them Mankiw (2012). The Willingness To Pay (WTP) to avoid the risk of a fatal injury increases proportionally with growing risk. 44 Given the conservative nature of this analysis and the transportationrelated nature of the injuries and deaths that could be reduced through timely accurate and complete use of more rigorous navigational data, the U.S. Department of Transportation's (DOT) figure of $9.4 million ($2015) was selected. 45

Value of Injury Reduction
The National Highway Transportation Safety Administration (NHTSA) has calculated comprehensive transportation-related accident costs through the "Maximum Abbreviated Injury Scale" (MAIS). 46   Beginning in 2011, the USCG reported not only the number of injuries but also the level of injury severity for each accident. 52 Of the 824 reported injuries during 2011 to 2015, over 59 percent were classified as "minor". 53 From this 47 The Department of Transportation refers to this scale as the "Abbreviated Injury Scale (AIS)". 48 Refer to Table 2 Table 2. 52 The USCG does not claim that its injury scale is the AIS scale. The descriptions of the levels in the CG and AIS are similar, such that the match-up in Table 3 provides a way to monetize injuries. This approach was used in the Inspection of Towing Vessel and other rulemakings. 53 While an additional 36 injuries were reported, upon closer examination, the USCG determined that their severity was less than "minor" and subsequently excluded from the analysis. distribution, the expected average cost of injuries, where severity had not been reported in earlier years, could be calculated (Table 6). Following this procedure, the average cost of an injury where severity was not delineated was estimated to be approximately $336,000 ($2015) (Table 7).   To estimate gross benefits of reduction in morbidity and mortality, overall accident rates were estimated predicated on average vessel transit counts during the 2008 to 2015 period. To ensure a conservative approach, vessel transits for locations with PORTS ® were compared with locations without PORTS ® . Adjustments were necessary to help ensure that vessel transit counts were not overstated for PORTS ® locations (Table 8) Based on the expected number of deaths and injuries that occurred during the study period, almost three fewer deaths and six fewer injuries occurred in areas with PORTS ® than would have been expected had PORTS ® not been installed. Employing a value of a life of $9.4 million and cost of an average accident of $0.34 million, annual reductions resulting from human-based losses were estimated at approximately $28.4 million. Over ten years, this would equate 54 About 148 thousand vessel transit counts were subtracted from locations with PORTS ® to reflect the time during an installation year when PORTS ® were yet to be installed. For example, if PORTS ® was installed in July of a given year that location vessel transits were not assigned to the "after" group (locations with PORTS ® ) until the following year. While this ultimately assigned some PORTS ® and other navigational aid benefits to the "before installation" group, it helped ensure a conservative approach where the number of transits with PORTS ® would be otherwise overstated.

DOT AIS SCALE
to a present value in excess of $244 million from 28 fewer deaths and 61 fewer injuries. 55

Property Loss Reductions
Property losses for the "average" ACG was estimated to exceed $71 thousand ($2015) ( Examination of the ACGs that occurred between 2008 and 2015 revealed the rate of ACGs where property loss occurred was 0.00019 per vessel transit at locations with PORTS ® and 0.00054 at locations without PORTS ® . Employing the differential in property loss rates suggests about 176 fewer incidents occur at locations with PORTS ® . This equates to over $13.5 million per year from an additional 189 property loss incidents that would have occurred. Over ten years this could exceed $116 million in savings.

POTENTIAL PORTS ® INSTALLATION VALUE
According to the USCG's MISLE database, during the 2005 to 2016 study period, 116 of the 163 port locations without PORTS ® experienced one or more ACG incidents. Almost 2,300 ACGs occurred within a ten-mile radius of port locations that did not have PORTS ® installed. Within a five-mile radius of locations without PORTS®, 1,514 ACGs were reported. Closer to each of these locations, 944 occurred within a three-mile radius of the ports without PORTS®. 55 Employing the 2.8 percent discount rate reflecting the expected ten-year life of PORTS ® instruments. Source: Office of Management and Budget, Circular Number A-94, January 21, 2015.
Collectively, within 10 mile radii, allisions accounted for 34 percent of events while collisions and groundings represented 27 and 39 percent, respectively. These accidents represented approximately $241 million ($2015) in total losses. The majority of these losses (67 percent) was from vessel, facility, cargo and other damages. Mortality and morbidity losses exceeded $28 million (12 percent) and $51 million (21 percent), respectively. 56 While average total losses from all ACG types averaged $106 thousand, one allision in 2013 represented orders of magnitude higher than historical levels and illustrates the potential high degree of variability over time. 57 Due to the overlap of area of influence should PORTS ® be installed in adjacent locations, along with lack of knowledge of the scope of such installations, it is not possible to develop a precise value of potentially averted losses. It is possible to identify the top 20 percent of non-PORTS ® locations where the largest number of ACGs occurred and estimate ACG rates through application of CPT transit counts (Table 10). 58 While not precise, it is also possible to project a less than perfect estimate of the maximum gross benefit that would occur if no overlap occurred. Costs resulting from morbidity, mortality and property damages at all locations without PORTS ® totaled in excess of $241 million (2,271 ACG events). Based on an average loss of about $106 thousand per ACG, if PORTS ® were to be installed at all remaining major inland and coastal ports with significant histories of ACGs, maximum added benefits would be less than $58 million based on attributing 51 percent of total reductions in losses to PORTS ® . 59

CONCLUSIONS
Precise estimation of reductions in ACG rates and resultant benefits among the myriad of individual navigational aids (e.g., PORTS ® , navigational maps, crew performance, pilot expertise, vessel design, etc.) is not practical, due to unknown utilization rates of the respective technologies as well as uncertainty concerning the degree to which these advances contribute to ACG rates reductions. 59 Refer to "Total" impact in Figure 7. However, it is more than coincidental that significant reductions in ACG rates occurred immediately following the installation of PORTS ® at 17 additional locations between 2008 and 2010, before and after installation at an identical group of seven ports, and in the longer term of 2008 to 2015 when PORTS ® coverage of vessel transits more than doubled (Figure 9). Installation of PORTS ® resulted in estimated reduction of annual losses approaching $42 million. Over ten years this equates to a present value savings of approximately $360 million. While historical estimates approach 72 percent, previous estimates (Wolfe 2016) of ACG rates employing only 2010 data may not have been representative of the longer term. From the current analysis, it would appear that installation of PORTS ® reduced overall ACG rates between 44 and 51 percent. Both approaches employed in the current estimation agreed with the earlier 20 to 60 percent range of reductions in grounding provided by Kite-Powell (2010). Interesting to note is the change in ACG rates that occurred at all other locations without PORTS ® . Between 2008 and 2015, ACG rates at these locations increased 28 percent (Table  11). 60 Future updating of this analysis when additional data becomes available can 60 These incidents occurred at all distances from shore.
assist in more precise estimation of the long-term impact of PORTS® on ACG rate reduction.