CARGO TANK 

TRUCKS

Improved Incident 

Data and Regulatory 

Analysis Would Better 

Inform Decisions 

about Safety Risks

Report to Congressional Committees

September 2013

GAO-13-721

United States Government Accountability Office
United States Government Accountability Office

Highlights of GAO-13-721, a report to 

congressional committees

September 2013

CARGO TANK TRUCKS

Improved Incident Data and Regulatory Analysis

Would Better Inform Decisions about Safety Risks

Why GAO Did This Study

Cargo tank trucks deliver gasoline and 

other flammable liquids daily for 

consumer use. Trucks are loaded and 

unloaded through external bottom lines 

that, after loading, may contain up to 

50 gallons of liquid and are known as 

“wetlines.” Concerns have been raised 

about the safety of wetlines, since a 

collision may rupture them, releasing 

flammable liquid and possibly causing 

fatalities and property damage. 

PHMSA is responsible for regulating 

the safe transportation of hazardous 

materials and has proposed rules 

prohibiting the transport of flammable 

liquids in wetlines. 

In 2012, The Moving Ahead for 

Progress in the 21st Century Act 

required GAO to examine this issue. 

This report discusses (1) the extent 

that PHMSA’s data reliably identify

wetline safety risks, (2) options for 

addressing wetline safety risks, and (3) 

how well PHMSA has assessed the 

costs and benefits of addressing these 

risks through regulation. GAO 

analyzed PHMSA’s wetline incident 

data for 1999 to 2011, reviewed

PHMSA’s regulatory cost-benefit 

analyses, and interviewed agency 

officials and industry and safety 

stakeholders.

What GAO Recommends

DOT should improve its wetline 

incident data by requiring carriers to 

specifically report wetline incidents and 

by improving its information on incident 

consequences. DOT should also 

address uncertainty in the assumptions 

and data underlying its regulatory costbenefit analysis. DOT did not agree or 

disagree with the recommendations, 

but provided technical comments.

What GAO Found

The Department of Transportation’s (DOT) Pipeline and Hazardous Materials 

Safety Administration’s (PHMSA) incident data cannot be used to reliably identify 

risks from incidents involving collisions with and spills from tank trucks’ bottom 

lines (“wetlines”) because the incidents are not specifically identified in PHMSA’s

database and the data contain inaccuracies. PHMSA requires carriers to report 

hazardous material incidents, but the reporting form does not specifically capture 

wetline incidents. PHMSA officials identify wetline incidents through a resourceintensive process of reviewing carrier-reported incident narratives and other 

information. However, GAO found that the narratives do not always clearly 

indicate whether an incident is wetline related and that information about the 

consequences of incidents, including fatalities, is not always accurate. PHMSA 

has made efforts to improve its data, such as adding quality checks, but this has 

not affected how wetline incidents are reported, and inaccuracies remain.

One technology to purge liquid from wetlines exists, but use of this system is 

limited, and industry and safety stakeholders expressed concerns about it, such 

as concerns about the safety of retrofitting existing trucks with the device and its 

cost. Although other options have been proposed to address wetline risks, none 

has been pursued, and there are concerns about their safety and feasibility as 

well. For example, wetlines could be drained at loading terminals, but this creates 

issues over storing the drained fuel and whether it could be resold.

PHMSA analyzed the costs and benefits of its proposed 2011 rule to prohibit 

transportation of flammable liquids in unprotected wetlines, but did not account 

for uncertainties in its analytical assumptions and limitations in the underlying 

incident data. For example, PHMSA’s analysis overstated the number of fatalities 

the proposed rule would prevent when considering actual past incidents.

Furthermore, PHMSA based its cost analysis on the assumption that carriers 

would install a certain type of wetline purging system, but its limited adoption 

makes that cost uncertain. Federal guidance recommends that agencies account 

for uncertainty in regulatory analysis, such as limitations in PHMSA’s data and 

uncertainty in its assumptions. Without having done so, PHMSA’s analysis may 

not accurately represent the costs and benefits of its proposed rule.

Examples of Wetline Incidents

View GAO-13-721. For more information, 

contact Susan A. Fleming at (202) 512-2834

or flemings@gao.gov.
Page i GAO-13-721 Cargo Tank Trucks

Letter 1

Background 3

PHMSA’s Incident Data Cannot Be Used to Reliably Identify 

Wetline Incidents, Although Efforts to Improve Data Quality 

Have Been Implemented 11

Stakeholders Identified Existing and Potential Options to Address 

Wetline Risks, but Have Concerns about Safety, Costs, and 

Implementation 24

PHMSA Analyzed Costs and Benefits for a Proposed Wetlines Rule, 

but Uncertainties Limit the Usefulness of the Analysis 32

Conclusions 40

Recommendations for Executive Action 41

Agency Comments 41

Appendix I Objectives, Scope, and Methodology 43

Appendix II PHMSA’s Wetline Proposed-Rule Cost-Benefit Methodology and 

Related Changes 48

Appendix III GAO Contact and Staff Acknowledgments 51

Tables

Table 1: Extent That Narratives on PHMSA-Identified Wetline 

Incidents Clearly Characterized Incidents as WetlineRelated, January 1999 through March 2011 18

Table 2: Stakeholders’ Views on Options to Address Wetline Risks 30

Table 3: Costs and Benefits Included in PHMSA’s 2011 Cost-Benefit 

Analysis and Its 2012 Draft Revision 34

Table 4: Wetline Industry and Safety Stakeholders Interviewed 45

Table 5: Cost and Benefit Values and Calculation Methodologies 

from PHMSA’s 2011 and 2012 Wetline Proposed-Rule CostBenefit Analyses 50

Contents
Page ii GAO-13-721 Cargo Tank Trucks

Figures

Figure 1: Cargo Tank Truck Components That Pertain to Loading, 

Transporting, and Unloading of Flammable Liquids 4

Figure 2: A Typical Process for Loading, Transporting, and 

Unloading Cargo Tank Trucks Carrying Flammable 

Liquids 6

Figure 3: Examples of Wetline Incidents 9

Figure 4: Timeline of Key Events and Federal Regulatory Actions 

on Wetlines 11

Figure 5: The Main Components of Cargo Tank Concepts’ 

Automatic Wetline Purging System 25
Page iii GAO-13-721 Cargo Tank Trucks

Abbreviations

DOT Department of Transportation

hazmat hazardous material

MAP-21 Moving Ahead for Progress in the 21st Century Act

NTSB National Transportation Safety Board 

OMB Office of Management and Budget

PHMSA Pipeline and Hazardous Materials Safety Administration

This is a work of the U.S. government and is not subject to copyright protection in the 

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without further permission from GAO. However, because this work may contain 

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necessary if you wish to reproduce this material separately.
Page 1 GAO-13-721 Cargo Tank Trucks

441 G St. N.W.

Washington, DC 20548

September 11, 2013

The Honorable John D. Rockefeller, IV

Chairman

The Honorable John Thune

Ranking Member

Committee on Commerce, Science, and Transportation

United States Senate

The Honorable Bill Shuster

Chairman

The Honorable Nick J. Rahall, II

Ranking Member

Committee on Transportation and Infrastructure

House of Representatives

Americans rely on flammable liquids such as gasoline for daily personal 

and industrial use, but transporting these liquids poses inherent safety 

risks to people and property. Cargo tank trucks transporting flammable 

liquids in the United States are loaded and unloaded through external 

pipes under the tank compartments. These pipes, when they contain 

flammable liquid, are known as “wetlines” and can collectively carry up to 

50 gallons of liquid per truck. The National Transportation Safety Board 

(NTSB), among others, has identified wetlines as a potential hazard 

because a broadside collision with a tank truck can rupture the wetlines, 

spilling flammable liquid and creating the potential to fuel fires and 

therefore increased damage and fatalities from such incidents. In 1997, 

such an incident occurred in Yonkers, New York, when a passenger car 

collided with a tank truck under a highway overpass. The collision 

ruptured the truck’s wetlines, resulting in a passenger fatality and the 

destruction of the overpass. The incident, cleanup, and subsequent 

infrastructure repairs created significant and costly traffic delays in the 

region.

In 1998, after investigating the Yonkers incident, NTSB recommended 

that the Department of Transportation (DOT) prohibit transportation of all 

hazardous materials in wetlines. DOT subsequently proposed rules to 

prohibit the transportation of flammable liquids in unprotected external 

product piping (“wetlines”), but did not adopt final rules in those 

proceedings. In January 2011, the Pipeline and Hazardous Materials 

Safety Administration (PHMSA), an operating administration of DOT, 

again proposed a rule to prohibit the transportation of flammable liquids in 

unprotected wetlines and released an initial analysis of the proposed 
Page 2 GAO-13-721 Cargo Tank Trucks

rule’s costs and benefits. PHMSA updated its cost-benefit analysis in 

March 2012, but did not release this version publicly. The Moving Ahead 

for Progress in the 21st Century Act (MAP-21), enacted in July 2012, 

temporarily stopped PHMSA from issuing a final wetlines rule except in 

very specific circumstances1

To evaluate the extent that PHMSA’s data can be used to reliably identify 

wetline safety risks, we examined PHMSA’s process for identifying 

wetline incidents among its reported hazardous materials (hazmat) 

incidents, analyzed how useful PHMSA’s incident data from January 1999 

through March 2011 are for identifying such incidents,

and required us to examine the risks of and 

alternatives to transporting flammable liquids in wetlines. In this report we 

discuss: (1) the extent that PHMSA’s data can be used to reliably identify 

wetline safety risks, (2) options for addressing wetline safety risks, and (3) 

how well PHMSA has assessed the costs and benefits of addressing 

these risks through regulation.

2

 1

Pub L. No. 112-141, 126 Stat. 405, 840-41 (2012). Section 33015 of MAP-21 prohibits 

DOT from issuing a wetlines final rule prior to either the completion of our mandated study 

or until July 2014, whichever is earlier, unless DOT determines that a risk to public safety, 

property, or the environment is present or an imminent hazard exists and that the 

regulations will address the risk or hazard.

and examined 

whether these data accurately captured information about the incidents’

consequences. We reviewed the reliability of these data by examining 

them for missing data and inconsistencies, reviewing PHMSA’s process 

for obtaining wetline incident data and maintaining them in the agency’s 

incident database, and reviewing the agency’s related internal controls. 

We concluded that the data were sufficiently reliable for the purposes of 

our report. To describe options for addressing wetline safety risks, we 

identified options by reviewing documents filed in the current and prior 

PHMSA wetline safety rulemakings and interviewing petroleum and 

related transportation industry and safety stakeholders (see app. I for a 

list of stakeholders we interviewed). We also asked stakeholders about 

their views on the advantages and disadvantages of these options and 

reviewed comments filed in the most recent PHMSA wetline rulemaking. 

We placed particular focus on examining the wetline purging system, 

because it is the option used in PHMSA’s wetlines rulemaking analysis 

and the only option we identified that has been installed to address 

wetline risks. To evaluate how well PHMSA has assessed the costs and 

benefits of its January 2011 proposed wetline rule, we reviewed PHMSA’s 

2

We examined incident data from January 1999 through March 2011 because this is the 

period of time of the incidents PHMSA used to support its wetline rulemaking.
Page 3 GAO-13-721 Cargo Tank Trucks

associated regulatory cost-benefit analysis, examined the reliability of 

PHMSA’s supporting wetline incident data used to inform the analysis, 

and interviewed PHMSA officials about their efforts. See appendix I for a 

more detailed description of our objectives, scope and methodology.

We conducted this performance audit from September 2012 to 

September 2013 in accordance with generally accepted government 

auditing standards. Those standards require that we plan and perform the 

audit to obtain sufficient, appropriate evidence to provide a reasonable 

basis for our findings and conclusions based on our audit objectives. We 

believe that the evidence obtained provides a reasonable basis for our 

findings and conclusions based on our audit objectives.

Every day, tens of thousands of cargo tank trucks transport hazardous 

materials classified as flammable liquids (primarily gasoline and fuel oil) 

for sale in the United States.3 This involves some safety risk because of 

the volatile nature of flammable liquids, the volume of liquid transported 

(up to 9,200 gallons per truck), and the numbers of trucks and passenger 

vehicles on the road. Tank trucks that carry flammable liquids have three 

main components—the truck, the trailer, and the cargo tank. The tank 

may be divided into several compartments—usually four or five—allowing 

the truck to carry different petroleum products in a single trip, such as 

different grades of gasoline and diesel fuel. Although the design of cargo 

tank trucks can vary depending on the model and manufacturer, the 

components in figure 1 are common features.

 3

The exact number of cargo tank trucks operating in the United States is unknown since 

DOT does not track this information. For the purposes of the proposed wetline rule, 

PHMSA’s regulatory assessment assumes a total of 27,000 tank trucks would be affected 

by a rule. Citing others’ research, NTSB has indicated that other estimates have ranged 

from about 10,000 to 60,000 tank trucks. See NTSB, Safety Recommendation, H-11-1 

(Washington, D.C.: Sept. 2, 2011).

Background

Flammable Liquid 

Distribution
Page 4 GAO-13-721 Cargo Tank Trucks

Figure 1: Cargo Tank Truck Components That Pertain to Loading, Transporting, and Unloading of Flammable Liquids

a

Weight restrictions limit a cargo tank truck’s operating capacity to between 7,500 and 9,200 gallons 

of liquid, which is usually less than the tank’s total capacity.
Page 5 GAO-13-721 Cargo Tank Trucks

The rule proposed by PHMSA in January 2011 would require that 

flammable liquids be eliminated from bottom loading and unloading lines, 

such as by purging the bottom lines of product, or that bottom lines be 

protected with approved bottom protection devices.4

 4

Bottom damage protection devices must meet the requirements of 49 C.F.R. §178.337-

10, 49 C.F.R. §178.345-8(b), or the accident damage protection requirements of the 

specification under which the cargo tank motor vehicle was manufactured.

The rule would apply 

to cargo tank trucks that typically transport gasoline, diesel, and fuel oil 

from distribution terminals—of which there are nearly 400 nationwide—to 

retail outlets or gas stations (see fig. 2).
Page 6 GAO-13-721 Cargo Tank Trucks

Figure 2: A Typical Process for Loading, Transporting, and Unloading Cargo Tank Trucks Carrying Flammable Liquids

a

The brake bar interlock is a system that, when activated, applies the truck’s parking brakes. A driver 

lifts the brake bar to access the truck’s loading valves, immobilizing the truck during loading or 

unloading.
Page 7 GAO-13-721 Cargo Tank Trucks

In the 1980s, to address volatile organic compound emission reduction 

requirements,5 as well as worker safety issues, the petroleum industry 

changed cargo tank-loading procedures from loading through the 

manhole covers on the top of the truck to loading through the bottom 

lines. Prior to this change, the bottom lines were used for unloading only 

and therefore generally did not contain more than a residual amount of 

flammable liquids during transport. In using bottom lines for loading, 

because the lines are at the lowest point on the truck, they do not drain 

into the main tanks but contain fuel. Bottom lines containing fuel are 

referred to as “wetlines.”

Wetline incidents result from collisions involving tank trucks that lead to 

the release of flammable liquid from wetlines. Such incidents range from 

easily contained spills to catastrophic situations. Carriers that transport 

hazardous materials, including flammable liquids like gasoline, are 

required to report incidents involving the release of hazmat to PHMSA.6

Carriers, for example, must submit an electronic or paper incident 

reporting form within 30 days of the incident. This form is designed to 

provide information about the vehicle and container involved in the 

incident, the component of the container that failed, the type and quantity 

of product released, and, if applicable, fatalities, injuries, and the dollar 

value of significant damages associated with the incidents.7

 5

Volatile organic compounds present in vented gas are contributors to elevated ozone and 

haze.

The form also 

includes a space for carriers to write a descriptive narrative of the 

incident. Information from these forms appears in PHMSA’s publicly 

6

The carrier is the company with physical control of the shipment during its transportation, 

which may or may not be the same as the shipper, i.e., the company originally providing 

the product. Carriers transporting flammable liquids may be oil companies or tank truck 

carriers that haul a variety of products. 

7

In most cases, an accidental release of hazmat from a cargo tank will require a written 

report within 30 days of the incident, specifically, a Hazardous Material Incident Report, 

Form DOT F 5800.1. This report is also required for damage to the lading system, even 

without a release of hazardous materials. Additionally, immediate reporting may be 

required to the National Response Center, a Coast Guard-operated sole national point-ofcontact for all oil and chemical discharges into the environment in the United States. See 

49 C.F.R. §171.15-16. Although PHMSA’s incident-reporting regulations exempt certain 

specified small releases, such as from the connection or disconnection of loading or 

unloading lines, the PHMSA regulations require the reporting of any unintentional release 

of a hazardous material, such as gasoline, and do not otherwise exempt releases below a 

specified minimum quantity. 

Wetline Incidents and 

Reporting
Page 8 GAO-13-721 Cargo Tank Trucks

available web-based incident database.8

While most wetline incidents identified by PHMSA did not result in fires, 

spilled flammable liquid can ignite and create the potential for fatalities as 

well as increased property and environmental damages. Incidents may be 

the result of a tank truck striking a stationary object or a moving 

passenger vehicle striking the tank truck. Figure 3 shows examples of two 

types of wetline incidents.

According to PHMSA, it uses the 

database for its safety oversight work, including regulatory efforts.

 8

PHMSA’s incident database is available at 

https://hazmatonline.phmsa.dot.gov/IncidentReportsSearch/ (accessed May 14, 2013).
Page 9 GAO-13-721 Cargo Tank Trucks

Figure 3: Examples of Wetline Incidents

PHMSA is responsible for regulating the safe and secure transportation of 

hazardous materials to reduce the risks to people and the environment. In 

1989 and 1990, PHMSA’s predecessor, the Research and Special 

Programs Administration, promulgated final rules that prohibited external 

product piping, such as bottom lines, from retaining hazardous liquids 

unless the cargo tank truck is equipped with bottom damage protection 

devices.9

 9

See, e.g., 54 Fed. Reg. 24982 (June 12, 1989); 55 Fed. Reg. 21035 (May 22, 1990); 55 

Fed. Reg. 37028 (Sep. 7, 1990).

Citing concerns about the potential costs of modifying fuel 

DOT Wetline Initiatives, 

1989–2012
Page 10 GAO-13-721 Cargo Tank Trucks

terminal operations, the lack of data on incidents, and the lack of 

information on possible alternatives to empty wetlines after bottom 

loading, the Research and Special Programs Administration exempted 

tanks transporting gasoline and other flammable liquids from the 

regulation.10 Thus, the resulting regulations, in general, pertain to certain 

poisonous liquids, oxidizer liquid, liquid organic peroxide, or corrosive 

liquids, but not to gasoline.11

The 1997 Yonkers incident drew attention to the safety risks of wetlines 

because it involved a fatality as well as unusually high damages. 

Specifically, its destruction of a highway overpass resulted in severe 

property damage, and the incident’s location in a congested area led to 

severe economic costs. Following NTSB’s recommendation that DOT 

prohibit transport of hazardous materials in wetlines,12 DOT (through the 

Research and Special Programs Administration and later PHMSA) 

submitted a draft proposed rule to the Office of Management and Budget 

(OMB) to address the issue in 2000 and later issued a proposed rule in 

2004. PHMSA withdrew its 2004 proposed rulemaking in 2006 because it 

concluded that the benefits of the rule would not justify the costs.13

 10A key concern over addressing this issue at the terminal, which industry stakeholders 

reiterated to us, is that fuel taxes are assessed through a metering system once the 

product is loaded onto a truck. To then drain some of the product from the wetlines would 

create an accounting problem, in addition to the issue of whether the product could be 

resold or would have to be disposed of.

PHMSA proposed another wetline rule in 2011. Figure 4 shows the 

timeline of key events and major regulatory efforts to address wetline 

risks.

1149 C.F.R. § 173.33(e).

12The NTSB considers the practice of transporting flammable liquids in wetlines to be an 

unsafe practice and contends that incidents similar to the Yonkers incident are likely to 

occur in the future. 76 Fed. Reg. 4847, 4848 (Jan. 27, 2011).

13Office of Management and Budget, Regulatory Analysis, OMB Circular No. A-4 (Sept. 

17, 2003), which implements Executive Order 12866, Regulatory Planning and Review

(Washington, D.C.: Sept. 30, 1993), requires agencies to assess the costs and benefits of 

specified types of proposed significant regulatory actions to analyze whether the expected 

benefits of the regulation are likely to justify its costs.
Page 11 GAO-13-721 Cargo Tank Trucks

Figure 4: Timeline of Key Events and Federal Regulatory Actions on Wetlines

a

Section 33015 of MAP-21 prohibits DOT from issuing a wetlines final rule prior to either the 

completion of GAO’s mandated study or until July 2014, whichever is earlier, unless DOT determines 

that a risk to public safety, property, or the environment is present or an imminent hazard exists and 

that the regulations will address the risk or hazard.

PHMSA’s incident data do not reliably capture the risks and 

consequences of wetline incidents because these incidents are not 

specifically identified in its database, and PHMSA’s incident data also 

contain inaccuracies. Although PHMSA requires reporting of hazmat 

incidents through incident reporting forms, it does not require carriers to 

explicitly state on the form whether the incident is wetline-related. 

Consequently, to identify wetline incidents, PHMSA officials must review 

carrier-reported narratives and other information, a review that is 

resource-intensive. Moreover, this review may not result in an accurate 

accounting of the number and consequences of wetline incidents 

because the information does not always clearly indicate whether the 

incident is wetline-related and because of inaccuracies and omissions in 

the data. PHMSA has made efforts to improve its data, such as 

implementing quality checks, but this does not affect how wetline 

incidents are reported, and errors remain. This limits the usefulness of 

these data as supporting information for PHMSA’s wetline regulatory 

analysis.

PHMSA’s hazmat incident database does not specifically code incidents 

as wetline-related because its incident reporting form does not require 

carriers to explicitly report whether an incident is wetline-related. 

Consequently, it is not possible to retrieve a list of wetline incidents 

through PHMSA’s database. To identify wetline incidents, PHMSA staff 

must analyze incident narratives and other carrier-reported information for 

PHMSA’s Incident 

Data Cannot Be Used 

to Reliably Identify 

Wetline Incidents, 

Although Efforts to 

Improve Data Quality 

Have Been 

Implemented

Limitations with PHMSA’s 

Incident Data Make It 

Difficult to Identify Wetline 

Incidents
Page 12 GAO-13-721 Cargo Tank Trucks

characteristics that are indicative of wetline incidents.14

Annually, PHMSA receives reports of about 15,000 to 20,000 hazmat 

incidents, and the percentage of these incidents that PHMSA identified as 

wetline-related is relatively small. To support PHMSA’s 2011 cost-benefit 

analysis, PHMSA officials said that a team spent months reviewing 

incident data to identify wetline incidents and, as of January 2011, 

identified 172 wetline incidents occurring over the 10-year period from 

January 1999 through December 2008.

This makes 

identifying these incidents resource-intensive and somewhat subjective, 

since the determination of which incidents are wetline-related is not 

always based on complete information, as incident data may be unclear 

or missing. OMB guidance states that agencies should develop a process 

for reviewing information quality as part of information resources 

management, including when collecting and maintaining the information 

to be used for regulatory analysis, which is one of PHMSA’s uses for its 

incident data.

15

 14According to PHMSA’s draft March 2012 regulatory analysis, a wetline incident is a 

reported incident meeting three criteria: 1) PHMSA can reasonably determine the incident 

involved damage or rupture to one or more of a cargo tank truck’s wetlines; 2) flammable 

liquid was released; and 3) any reported fatalities, injuries, and damages were directly 

attributable to the release of product from the wetline.

These incidents were used in 

the January 2011 proposed rule and related cost-benefit analysis. 

According to PHMSA’s updated March 2012 draft cost-benefit analysis, 

after commenters in the wetline rulemaking docket questioned whether 

some of these incidents should have been identified as wetline incidents, 

PHMSA reexamined the 172 incidents it originally identified and updated 

the analysis to include incidents through March 2011. This led PHMSA to 

a provisional figure of 132 wetline incidents, which PHMSA used in its 

15PHMSA’s initial review to identify wetline incidents was conducted by a team of five or 

six people over the course of about 2 to 3 months. Although PHMSA did not track 

resources used to identify wetline incidents, officials said the process took about 10 

minutes per incident reviewed and estimated the total effort between the initial review and 

a later review to identify incidents from 2009-2011 used about 1,200 staff hours.

Wetline Incident Identification
Page 13 GAO-13-721 Cargo Tank Trucks

updated 2012 draft cost-benefit analysis.16

To identify wetline incidents for both the 2011 and 2012 reviews, PHMSA 

officials said they conducted a broad search of cargo tank truck incidents 

in the database and then reviewed incident reports’ narrative descriptions. 

If a description was insufficient to make a determination, officials 

reviewed the content of other fields in the incident’s database entry such 

as component failure information, packaging identification, the amount 

and type of hazardous material released, and location of the vehicle at 

the time of the accident. PHMSA officials said their incident database 

provided sufficient information about incidents to make a judgment about 

each incident. However, the amount of time, staff, and specialized 

knowledge required for this process was more extensive than if PHMSA 

required carriers to identify whether incidents are wetline-related on the 

incident reporting forms. Officials also stated that, since their method of 

identifying wetline incidents by reviewing narrative descriptions required 

substantial resources, the agency was not able to direct additional 

resources to follow up with carriers to clarify missing or unclear data as 

part of the review to identify wetline incidents, except in cases involving 

fatalities.

Because PHMSA has not 

issued a final rule on this subject, information in either the 2011 or draft 

2012 analysis is subject to change.

In identifying consequences of wetline incidents, PHMSA has little 

information besides what is provided by the carriers. Specifically, only one 

wetline incident that occurred during the 1999 to 2011 incident study 

period was investigated by NTSB and PHMSA, and PHMSA officials said 

they were unaware of any other investigations of wetline incidents by 

 16In identifying incidents, PHMSA officials said they focused on those that would be 

affected by the proposed rule. For example, PHMSA cut 44 incidents from the original list 

of 172 identified incidents reported as involving a liquid release of greater than 50 gallons 

without a fire, under the assumption that since wetlines generally hold no more than 50 

gallons of liquid, a spill of greater quantity would indicate a tank compartment breach or 

internal valve failure. In total, PHMSA cut 59 incidents from its original figure of 172 and 

added 19 new incidents from a review of incidents occurring from January 2009 through 

March 2011. There were less than 20 incidents in any given year from 1999-2011 that fall 

into this group of 132 wetline incidents. There were 16 incidents that involved fires and 7 

that had one or more fatalities, which tended to involve occupants of the passenger 

vehicles.
Page 14 GAO-13-721 Cargo Tank Trucks

federal, state, or local authorities during this period.17

PHMSA officials stated that they considered a number of factors in 

identifying wetline incidents for the 2011 proposed rule, such as 

characteristics that could indicate an incident was wetline-related in the 

absence of more definitive information and exceptions included in the 

proposed rule that would exclude certain incidents. For example, PHMSA 

officials told us they considered any tank truck incident involving a 

collision or crash with a fire to be a wetline incident, regardless of the 

amount of released flammable liquid.

Therefore, 

PHMSA’s record of the consequences of wetline incidents is based 

almost solely on information provided by carriers without corroborating 

information from other sources. Additionally, information provided by 

carriers is not always clear. For example, PHMSA officials said that 

carriers may misidentify components or use colloquialisms in the narrative

(such as “fill tube” or “drop tube”) to denote bottom lines. Further, officials 

said that terminology used in the report could vary depending on whether 

the carrier’s corporate safety officer, the driver, or an attorney fills out the 

form.

18

 17The investigated incident occurred in Pilesgrove, New Jersey in 2009. See NTSB, 

Hazardous Materials Accident Brief, DCA-09-FZ-001 (Washington, D.C.: Nov. 12, 2009) 

and PHMSA, Inspection/Investigation Report No. 09323047 (Landisville, N.J.: July 2, 

2009). According to PHMSA officials, in 2012, the agency initiated a thorough review and 

follow-up audits of all incidents that resulted in death or injury, which officials believe will 

increase the likelihood of identifying wetline incidents.

The specific cause of incidents 

involving fires may be difficult to pinpoint, since the fire may destroy the 

forensic evidence needed to make that determination. Therefore, PHMSA 

officials assumed that incidents where the fire was not attributable to any 

one part of the vehicle were wetline-related because this approach would 

be less likely to exclude a severe incident that was caused by wetlines. 

However, this also means that the analysis could include severe incidents 

where the fire was the result of other factors, such as a puncture to the 

cargo tank. PHMSA officials stated that punctures to the cargo tank 

require forceful impact and are rare in incidents that do not involve a truck 

overturn. Therefore, in tank truck incidents with large spillages and fires, 

the fire likely began from the release of flammable liquid from bottom 

lines, according to PHMSA officials. Stakeholders disagree on whether 

this is a reasonable approach, with some supporting it because it can 

18As previously discussed, wetlines hold a total of up to about 50 gallons of flammable 

liquid, so PHMSA excludes incidents reporting more than this amount that do not involve a 

fire.
Page 15 GAO-13-721 Cargo Tank Trucks

address potential underreporting of incidents with fires and others stating 

that the practice artificially magnifies the benefits of the proposed 

regulation by including incidents that would not be prevented by 

eliminating wetlines.19 In applying regulatory factors to the identification of 

wetline incidents, PHMSA excluded some incidents involving bottom line 

spillage due to exceptions in the proposed wetlines rule, such as 

incidents involving smaller trucks that the proposed rule would exclude 

from regulation.20

In determining whether particular incidents were wetline-related, PHMSA 

did not clearly document its decision-making process. For example, in 

reviewing incidents that occurred from 2009 to 2011, PHMSA identified 

13 incidents as “possibly” wetline-related from the incident narrative 

information and subsequently used other incident information in making a 

final determination that 7 of those incidents were wetline-related.21

Our review of the reported incident data and narratives confirmed that it is 

challenging to identify wetline incidents. Using incident data other than 

the narratives, we attempted to identify wetline incidents on the basis of 

common characteristics of such incidents—involving a cargo tank truck, a 

release of flammable liquid, bottom line failure, and spillages or fires. In 

Although officials documented these incidents in a spreadsheet, they did 

not include details about the specific decision-making process PHMSA 

used to make a final determination for each incident. Therefore, it is not 

clear how the agency concluded that 7 of the 13 “possibly” wetline-related 

incidents were wetline-related and that the other 6 incidents were not.

 19Industry stakeholders questioned whether any incident involving the release of more 

than 50 gallons of flammable liquid should be considered a wetline incident. PHMSA 

officials said they consider this legitimate because fires initiated by a wetline release could 

spread and compromise the main tank.

20The January 2011 proposed rule exempts smaller trucks, known as straight trucks, that 

are built with the cargo tank attached to the main truck rather than the larger truck-andtrailer style of truck as depicted in figure 1 because the truck’s structure is assumed to 

provide sufficient protection for the wetlines.

21For example, PHMSA officials told us they identified a 2010 Portsmouth, Ohio, incident 

as wetline-related, despite the fact that its narrative description did not mention loading 

lines and its failure codes were left blank. Instead, PHMSA considered the type of vehicle 

(DOT-406 tank truck) and release amount (20-25 gallons) in the incident, which indicated 

to officials that this was a wetline incident since they believed a tank fracture would 

release much more product. Conversely, officials said that some incidents on the possibly 

wetline-related list were ruled out because, for example, their database entries indicated 

that wetlines were impacted but no release occurred.

Incident Data Limitations
Page 16 GAO-13-721 Cargo Tank Trucks

doing so, we were unable to generate a list of incidents that approximated 

PHMSA’s list of wetline incidents. Specifically, our search of the database 

turned up approximately 270 incidents from January 1999 through March 

2011 that PHMSA did not identify as wetline-related because they 

involved driver error or spills from areas other than wetlines, among other 

reasons.22 Conversely, some PHMSA-identified wetline incidents did not 

show up in our search results for reasons such as that they were coded 

as involving portable tanks instead of cargo tanks, indicating probable 

carrier error in reporting the incident.23

Additionally, inconsistencies with the component failure information in 

PHMSA’s incident data limit the usefulness of this information for 

identifying wetline incidents. The incident reporting form has a field for 

carriers to report up to two components that were the most catastrophic 

failure points in the incident, such as reporting failure of the bottom 

lines.24 PHMSA officials told us that although reporting this information is 

not optional, carriers sometimes leave this field blank, and the electronic 

version of the form lacks controls to force the entry of data in this field. 

Furthermore, carriers sometimes provide inaccurate information. For 

example, among the 132 incidents PHMSA identified as wetline-related, 

99 of the database entries for those incidents either did not list a code 

indicating bottom-line failure or had blank codes.25

 22Our review does not suggest that these could possibly be wetline incidents; in fact, 

PHMSA officials pointed out reasons why such incidents could have other factors not 

easily detected in a cursory data review that would indicate they are not wetline incidents. 

As discussed in our report, because of limitations with how incidents are reported, 

PHMSA’s process for identifying wetline incidents is resource-intensive and took months 

to complete for its regulatory analysis. A similar approach to identify wetline incidents was 

beyond our scope. Further, because of concerns about the reliability of PHMSA’s data, we 

would not be able to independently identify wetline incidents without additional 

corroborating information.

PHMSA’s guidance for 

filling out the incident reporting form includes a list of possible failure 

23Under PHMSA regulations, portable tanks are not to transport hazardous materials 

unless they meet additional specifications. 49 C.F.R. § 173.32. In these instances, as 

PHMSA officials noted, it is likely that carriers misidentified the packaging type.

24Officials said the “loading/unloading line” and “inlet valve” codes, technically correspond 

to bottom lines, and carriers can use these codes to identify bottom line failure. However, 

as we discuss in the report, carriers use the codes in a minority of cases.

25For example, 77 PHMSA-identified wetline incidents indicated the “hose” or 

“piping/fitting” as the part that failed, terms that could refer to a range of other equipment, 

such as the hose a driver would use to deliver product to underground tanks at a gas 

station.
Page 17 GAO-13-721 Cargo Tank Trucks

codes, but does not provide definitions of the codes. PHMSA officials said 

they do not have much confidence in using the failed components 

information for identifying wetline incidents. PHMSA officials 

acknowledged that missing data make it difficult to analyze incidents, but 

also said that the agency does not follow up with the carrier in these 

cases to confirm or correct the information unless the incident involves 

fatalities or injuries.26

Our review of the narratives for the 132 PHMSA-identified wetline 

incidents revealed that almost one-third of the narratives did not clearly 

identify the incidents as wetline-related because they lacked sufficient 

detail about the incident, used inconsistent terminology, or were blank. 

For example, some narratives indicated damage to other components 

that could have been the source of the spill. Other narratives did not 

indicate a collision resulting in a flammable liquid release. We also found 

instances of inconsistency in the database, such as narrative descriptions 

that did not corroborate other information provided in the database 

entry.27 Table 1 shows the extent to which we were able to identify wetline 

incidents from the narratives.

 26PHMSA officials said they are currently conducting a 6-month pilot test where staff are 

following up with carriers to obtain missing or inaccurate failure causes of tank truck 

hazmat incidents. However, according to PHMSA officials, it is not current agency policy 

to follow up on any fields other than fatalities and injuries. PHMSA officials said they 

conducted some follow up activity for all fatalities occurring in incidents cited in the draft 

March 2012 analysis. 

27For example, the narrative for a 2010 Brighton, Colorado, incident reported a spill of 

over 135 gallons, but the field in the database indicated that the quantity released was 30 

gallons.

Unclear Incident Narratives
Page 18 GAO-13-721 Cargo Tank Trucks

Table 1: Extent That Narratives on PHMSA-Identified Wetline Incidents Clearly 

Characterized Incidents as Wetline-Related, January 1999 through March 2011 

Extent that 

incidents were 

clearly wetlinerelateda

Number 

of 

incidents Examples of incident descriptionsb

Clearly wetlinerelated 

93 • Bottom lines were impacted by a collision, 

causing a spill. The compartment above the line 

was not affected.

• Bottom lines hit a post or pole at a gas station, 

causing a small release.

• A passenger vehicle ran a red light and struck a 

trailer at the valves of the bottom lines, damaging 

the lines and resulting in a release and immediate 

fire.

Unclear if wetlinerelated

38 • The bottom line or internal valve leaked.

• Bottom lines were damaged and minor tank 

damage also occurred.

• A trailer struck an unattended vehicle.

• A truck rolled over and gasoline spilled from the 

damaged trailer.

• More than 50 gallons of liquid—the amount that 

would typically be in wetlines—were released 

from a tank truck after a collision.

• Pipes froze and broke.

No narrative 

provided 

1

Total 132

Source: GAO Analysis of PHMSA incident data.

a

We assigned incidents to each category based on decision rules using PHMSA’s definition of a 

wetline incident.

b

Descriptions are paraphrased from actual incident narratives because carriers tended to use jargon 

and shorthand when describing the incidents.
Page 19 GAO-13-721 Cargo Tank Trucks

In addition to the limitations in identifying the number of incidents, we also 

found PHMSA’s incident data inaccurately portray the consequences of 

wetline incidents, thus limiting their reliability for regulatory analysis. 

Internal control standards for federal executive branch agencies require 

that agencies have relevant, reliable, and timely information for decisionmaking and external reporting purposes.28 OMB also has data quality 

guidelines for regulatory purposes.29

• Fatality Data. Among the 132 wetline incidents identified by PHMSA 

since 1999, there are 7 that PHMSA’s incident data show had one or 

more fatalities, with a total of 11 fatalities.

Because much of the economic 

benefit of the proposed wetline regulation would be the avoided fatalities 

and damages from wetline incidents, inaccuracies in these data raise 

concerns about their reliability for accurately quantifying some benefits of 

the proposed rule. Specifically, we found problems with incident data 

related to fatalities and damages:

30

 28See, e.g., Federal Managers Financial Integrity Act of 1982, Pub. L. No. 97-255, 96 Stat. 

814 (1982), and GAO, Standards for Internal Control in the Federal Government,

However, the fatalities in 3 

of the 7 incidents were misclassified as to whether they were caused 

by a hazmat release and thus preventable by the elimination of 

wetlines. According to PHMSA’s incident-reporting guidance, hazmatrelated deaths are directly attributed to the release of hazmat, such as 

a fatality caused by a fire resulting from the release of gasoline from 

wetlines. Nonhazmat-related deaths could occur in a hazmat incident 

but are attributed to other causes, such as internal injuries resulting 

from blunt force trauma during a collision. This distinction can have 

significant implications for the proposed rule’s cost-benefit analysis. 

Since the avoidance of hazmat-related deaths is a major portion of the 

GAO/AIMD 00 21.3.1 (Washington, D.C.: November 1999).

29Office of Management and Budget, Regulatory Analysis, OMB Circular No. A-4

(Sept. 17, 2003). Circular A-4 states that federal agencies should assure compliance 

with OMB’s “Guidelines for Ensuring and Maximizing the Quality, Objectivity, Utility, and 

Integrity of Information Disseminated by Federal Agencies” in their regulatory analyses. 

Those guidelines state that, among other things, agencies “shall adopt a basic standard of 

quality (including objectivity, utility, and integrity) as a performance goal and should take 

appropriate steps to incorporate information quality criteria into agency information 

dissemination practices.”

30There is an additional 2000 Altoona, Pennsylvania, incident that the narrative says 

resulted in a fatality but that is not marked as such in the database fields that track 

fatalities. According to PHMSA’s draft 2012 cost-benefit analysis, the fatality in this 

incident is nonhazmat-related. Although this incident does not affect the wetline costbenefit analysis, it is another example of the inaccuracy of these data.

Problems with PHMSA’s 

Incident Data Limit Their 

Reliability for Regulatory 

Analysis, Even Though 

Improvement Efforts Have 

Been Taken
Page 20 GAO-13-721 Cargo Tank Trucks

rule’s calculated benefit, nonhazmat-related deaths are not included in 

the calculation as they would not be prevented by the rule. We found 

that fatalities in 2 of the 4 incidents recorded in PHMSA’s database as 

hazmat-related were actually nonhazmat-related according to 

documentation about the incidents, which we confirmed with PHMSA 

officials.31 Conversely, the fatality in 1 of the 3 incidents with fatalities 

recorded as nonhazmat-related was later determined to be hazmatrelated.32

• Other Damage Data. Information on the dollar value of incident 

damages was sometimes missing or potentially inaccurate, since 

costs reported as “$0” in the database may represent no cost or an 

unreported cost.33 PHMSA officials stated they have not always 

followed-up with carriers to obtain missing cost information and that 

carriers do not always have full cost information. Specifically, costs 

not incurred directly by carriers like response and cleanup costs may 

not be known to the carrier at the time of submitting the form.34

 31A 2001 Green Bay, Wisconsin, incident is recorded in the database as having four 

hazmat-related deaths, but PHMSA officials told us these fatalities were later determined 

to be nonhazmat-related. Additionally, a 2004 Taylor, Michigan, incident was originally 

recorded as having a hazmat-related fatality, but PHMSA recently changed its 

determination to a nonhazmat-related death and updated the database to reflect this. 

Further, incidents with minor costs might not reflect any costs 

because carriers are not required to report total costs of $500 or less; 

however, in such cases, the data do not indicate whether a cost of $0 

indicates an actual “no cost” that would not have to be reported or a 

greater cost that was unreported. Although carriers are expected to 

32In this case, PHMSA’s database showed the fatality in a 2009 Pilesgrove, New Jersey, 

wetline incident as nonhazmat-related, despite an NTSB investigation that determined the 

cause of the death to be a fire resulting from the release of flammable liquid from a tank 

truck’s wetlines. After we discussed this with PHMSA officials, they amended the incident 

data and supporting documentation to state that the fatality was hazmat-related. 

33The cost categories reportable to PHMSA are material loss (estimate of the cost of the 

product lost), carrier damage, property damage, response cost (including police and fire 

emergency response), and remediation (cleanup) cost. Cost fields marked as “$0” in the 

database could indicate the carrier reported it as blank (leaving a dash, or no value in the 

field) or as $0 in the original incident reporting form, making it impossible to tell whether 

the cost was unreported or actually $0.

34For example, for a 2004 incident in Taylor, Michigan, that involved a fire and a fatality, 

PHMSA officials said they made an attempt to confirm cleanup and property damage 

costs marked as “pending,” but the carrier did not have this information and PHMSA did 

not make further attempts to follow up on the costs.
Page 21 GAO-13-721 Cargo Tank Trucks

contact PHMSA with significant updates to cost estimates up to a year 

after reporting, officials stated that carriers often do not.

Concerns have been previously raised about the quality of PHMSA’s 

incident data, including its usefulness for identifying wetline incidents. In a 

2009 report on its data, PHMSA acknowledged the limitation that its 

wetline data analysis depends on reviewing narrative descriptions 

provided by carriers in reporting forms because wetline incidents are not 

specifically coded in the data.35 Also that year, senior PHMSA officials’

congressional testimony stated that identifying wetline incidents is staffintensive and requires detailed analysis of database entries.36 More 

recently, a 2013 National Academies Transportation Research Board 

report sponsored by PHMSA stated that detailed data on the nature of 

damages in incidents involving the release of hazardous materials are 

necessary for studying the performance of the container transporting the 

product. The report stated that while PHMSA’s database collects some of 

this information, it is not sufficiently detailed.37

To address concerns about its data, PHMSA has made data process 

changes intended to improve the accuracy and completeness of its 

incident database. For example, PHMSA officials said that in 2012 the 

agency initiated a thorough review and follow-up audits of all incidents 

that result in deaths or injuries, which they said increases the likelihood of 

identifying wetline incidents. However, these changes do not address that 

wetline incidents are not specifically identified through the incident 

reporting process and do not apply to the inaccuracies in older incident 

 35PHMSA, A Data Quality Assessment: Evaluating the Major Safety Data Programs for 

Pipeline and Hazardous Materials Safety (Washington, D.C.: Nov. 10, 2009).

36Reauthorization of the Department of Transportation’s Hazardous Materials Safety 

Program, Hearing before the Subcommittee on Railroads, Pipelines and Hazardous 

Materials of the Committee on Transportation and Infrastructure, House of 

Representatives. 111th Cong. 1 (May 2009) (statement of Cynthia Douglass, Acting 

Deputy Administrator, PHMSA, and Ted Willke, Associate Administrator, PHMSA)

37Transportation Research Board of the National Academies, Feasibility Study for 

Highway Hazardous Materials Bulk Package Accident Performance Data Collection

(Washington, D.C.: 2013).
Page 22 GAO-13-721 Cargo Tank Trucks

data. Some of the steps PHMSA has taken according to officials included 

the following:38

• In 2005, PHMSA updated its incident reporting form and process by, 

among other things, providing more specific options for identifying the 

part of the vehicle that failed and requiring carriers to submit report 

updates up to 1 year after an incident when information about incident 

fatalities or significant damages changes.

• Also in 2005, PHMSA implemented an electronic reporting option that 

incorporates checks to improve completeness before the form is 

approved in the database.39

• Since about 2 years ago, PHMSA has provided training and outreach 

to carriers on filling out the incident form more accurately and 

completely and to encourage online reporting.

• The agency implemented an improved data quality process starting in 

2009, including updating its incident database to correct information it 

determined to be inaccurate. Before that time, the agency generally 

did not make changes to carrier-reported information in the system. 

Specifically, PHMSA reviews submitted incident reporting forms for 

accuracy and completeness and conducts follow-up with carriers to 

resolve missing information in the database.40

• To address concerns about under-reporting of incidents, PHMSA 

attempts to discover potentially reportable incidents by reviewing 

incident reports submitted to the National Response Center and 

 38PHMSA officials told us they are engaged in an ongoing effort to improve incident data 

in response to requirements in MAP-21, which they said includes conducting an 

assessment to review and improve the collection, analysis, reporting, and use of data 

related to accidents and incidents involving the transportation of hazmat, including better 

data on tank truck incidents. Officials indicated the efforts would not be completed by the 

publication date of this report. Therefore, we were unable to assess how this effort may 

improve data on wetline incidents.

39For example, if a carrier indicates on the form that the damages from the incident totaled 

over $500, the electronic reporting form will force the entry of a dollar value for at least 

one specific type of damage.

40However, PHMSA officials stated the improvements are not retroactive to incidents 

occurring before 2005. 
Page 23 GAO-13-721 Cargo Tank Trucks

monitoring the news media.41

• In an effort to improve the accuracy of its fatality and injury data, 

PHMSA developed a worksheet to better track and confirm 

information about fatalities and injuries.

PHMSA tracks severe incidents that 

may need reporting by carriers and, if warranted, may contact the 

carrier to request submittal of a reporting form, a process that has 

identified some wetline incidents, according to PHMSA officials.

42 In 2012, PHMSA began 

working with the Federal Motor Carriers Safety Administration to 

investigate hazmat incidents involving fatalities, injuries, and fires. 

Also in 2012, PHMSA began retaining coroner’s or medical 

examiner’s reports associated with each fatality.43

Although these efforts could improve PHMSA’s incident data going 

forward, they have no effect on some of PHMSA’s older wetline incident 

data. The agency relied on data back to 1999 in analyzing costs and 

benefits of its proposed wetline rule. As previously discussed, upon 

reexamination of its data, PHMSA changed the number of wetline 

incidents supporting its current proposed rule. However, because of the 

subjective nature of how wetline incidents are identified, the possibility still 

exists that PHMSA’s identification of some incidents as wetline-related 

may be inaccurate. Industry stakeholders told us they believe PHMSA’s 

data overstate the prevalence of wetline incidents and that their low 

number does not justify regulation. Conversely, some safety stakeholders 

said such incidents may be underreported. Additionally, as we have 

mentioned earlier, we found inaccuracies in these data, limiting their 

reliability for accurately quantifying the consequences of wetline incidents. 

In particular, flaws with the fatality and damages data have the potential 

to skew calculations of the rule’s benefit of avoiding wetline-related 

 41Federal regulation requires notification to the National Response Center in the event of 

a hazardous material incident that meets specific criteria such as involving a fatality, an 

evacuation of the general public, or a shutdown of a transportation artery for 1 hour or 

more. See 49 C.F.R. § 171.15.

42The Death and Injury summary is a worksheet for PHMSA internal purposes in which 

staff record information confirmed each time they contact carriers. This is part of PHMSA’s 

overall quality control process for hazmat incident data.

43Although PHMSA officials said they have always reviewed these reports, the agency did 

not retain them prior to 2012 because of concerns about retaining personally identifiable 

information. More recently, the agency decided to begin retaining the reports under lock 

and key whereby interested parties might be provided redacted versions or information 

about the sources PHMSA obtained the reports from. 
Page 24 GAO-13-721 Cargo Tank Trucks

fatalities. This calls into question whether these data are sufficiently 

reliable to support regulatory analysis unless PHMSA makes adjustments 

for the potential uncertainty in the analysis. Without accurate data on the 

number and consequences of wetline incidents, the consequences of 

wetline incidents remain unclear and the benefits of wetlines regulation 

may not be accurately calculated in PHMSA’s regulatory analysis.

A purging system is a device a carrier or manufacturer can install on a 

cargo tank truck that removes liquid from the truck’s bottom lines after a 

driver finishes loading the cargo tanks at the fuel terminal. One company, 

Cargo Tank Concepts, manufactures a purging system that uses 

compressed air from an auxiliary tank to push the liquid in the bottom 

lines through small ancillary lines and into the cargo compartments (see 

fig. 5). When the purge is complete, the lines retain only residual amounts 

of liquid and vapor.

Stakeholders 

Identified Existing 

and Potential Options 

to Address Wetline 

Risks, but Have 

Concerns about 

Safety, Costs, and 

Implementation

An Existing Purging 

System to Address Wetline 

Safety Risks Is in Limited 

Use
Page 25 GAO-13-721 Cargo Tank Trucks

Figure 5: The Main Components of Cargo Tank Concepts’ Automatic Wetline 

Purging System

Cargo Tank Concepts designed two versions of the purging system: 

automatic and manual. With the automatic system, after the driver 

finishes loading the cargo tank, electronic sensors detect liquid in the 

bottom lines and the system automatically begins to purge. One major 

petroleum company installed the automatic purging system on its cargo 

tank truck fleet starting in the late 1990s.44 Cargo Tank Concepts has also 

equipped a few trucks owned by other carriers with the automatic version 

to demonstrate the purging system. The manual system engages when 

the driver pushes a button to activate the purge, typically after loading the 

cargo tank. According to the purging system manufacturer, as of June 

2013, there were no manual purging systems in use.45

 44The company is a terminal operator, carrier, and marketer. It transports and stores 

petroleum, operates terminals, and sells fuel at thousands of retail outlets.

PHMSA officials, 

three industry stakeholders, and two safety stakeholders told us that they 

anticipate other purging solutions would be developed if PHMSA’s 

45Cargo Tank Concepts told us in June 2013 that a carrier had contacted the company 

about purchasing and installing a manual system soon.
Page 26 GAO-13-721 Cargo Tank Trucks

proposed wetlines rule were to go into effect.46

Industry associations and companies, manufacturers, repair shops, 

federal agencies, and safety groups identified advantages and 

disadvantages of using a purging system to address wetline risks. Due to 

limited use, most stakeholders do not have first-hand experience with the 

wetline purging system and its performance. Thus, stakeholders’

familiarity with the more technical aspects of the system varied and some 

stakeholders, particularly safety groups, declined to comment. However, 

based on their expertise with cargo tank trucks and transporting 

flammable liquids, stakeholders provided views on using such a system in 

that operating environment.

We contacted two other 

manufacturers that an industry publication reported were developing 

wetline purging systems. Both companies told us they have not produced 

any systems other than prototypes; however, both said they could move 

forward with development, and eventually production, if PHMSA finalizes 

a wetlines rule.

According to stakeholders, the advantages of using a purging system 

include:

• Addressing wetline safety risks: Purging removes all but a residual 

amount of liquid from the bottom lines, in accordance with one of the 

ways to meet the standard in PHMSA’s proposed rule. Removing 

flammable liquid from the bottom lines may reduce fatalities and the 

number and severity of injuries in the event of a broad-side collision 

between a passenger vehicle and a cargo tank truck. The absence of 

liquid in the bottom lines may also reduce property and environmental 

damages associated with hazardous materials spilling from the 

bottom lines.

• Identifying faulty valves: Depending on the design of a purging 

system, it may permit detection of faulty internal emergency valves. If 

an emergency valve is not working properly, liquid may leak from a 

cargo tank compartment into the bottom lines. In the event of a 

collision with wetlines, a faulty emergency valve could cause a carrier 

 46Between January 1999 and January 2013, at least six patent applications for 

technologies to address wetline safety risks were filed with the U.S. Patent Office. Three 

of these applications, all granted, were for systems to purge wetlines, while two others 

were for systems designed to reduce the amount of liquid spilled in the event that a 

bottom line shears off from the cargo tank.
Page 27 GAO-13-721 Cargo Tank Trucks

to lose liquid from an entire cargo tank compartment. If a purging 

system attempts to purge liquid when the line should be clear, a driver 

may be alerted that there is a problem; if the driver were not alerted, 

the faulty valve could go undetected until the next inspection.

Stakeholders also raised a number of concerns about purging systems, 

but disagreed about the significance of them:

• Retrofitting: Industry stakeholders are concerned about the safety of 

installing purging systems on in-service tank trucks due to the risk that 

welding on the tanks—if not completely free of gasoline vapor—

creates a risk of explosion. Specifically, 9 industry stakeholders and 3 

safety groups we interviewed raised this issue, and 18 of the 21 of the 

industry associations and companies providing comment in response 

to PHMSA’s 2011 proposed wetlines rule reinforced those concerns 

as being a risk if the proposed regulation required retrofitting.47

However, stakeholders also acknowledged that there are procedures 

that allow welding to be done safely, and repair shops routinely weld 

on cargo tanks when they require repair. Cargo Tank Concepts did 

not characterize the concern about retrofitting as significant, but the 

company has developed a “nonwelded” alternative to address industry 

concerns, which it has installed on one truck. However, three industry 

stakeholders expressed concern about the durability of such an 

installation, two of whom added that the “nonwelded” alternative 

would still entail “hotwork” such as cutting into the tank.48 According to 

Cargo Tank Concepts, the nonwelded installation involves drilling but 

not cutting, welding or other types of “hotwork.”

• Installation time: Stakeholders’ estimates on the amount of time 

needed to install a purging system on an existing tank truck varied 

from 8 to 40 hours. While Cargo Tank Concepts provided the lowest 

estimate of 8 hours, an industry stakeholder with firsthand experience 

 47The extent that the proposed rule would require retrofitting depends on how much time 

the industry would be given to comply, with a shorter compliance period requiring more 

retrofitting than a longer one in which existing vehicles could be replaced by new ones that 

already have a purging system installed by the manufacturer.

48In assessing the feasibility of the purging system technology, PHMSA officials told us 

they observed the function of a prototype model of the purging system that was not 

installed on an actual cargo tank truck. Thus, PHMSA has not assessed the feasibility of 

the nonwelded installation, although officials told us they believed such construction 

techniques were in keeping with other aspects of cargo tank truck manufacturing.
Page 28 GAO-13-721 Cargo Tank Trucks

installing a purging system estimated that installation takes from 30 to 

34 hours of labor. The higher estimates include time to “de-gas” the 

cargo tank to reduce risk of explosion, increasing the cost of 

installation compared to that on new cargo tanks since those would 

not need to be de-gassed. PHMSA’s regulatory assessment that 

considers different timeframes for implementing a wetlines rule 

assumes such retrofitting could be done concurrent with 5-year 

interval inspections, which involve de-gassing the tank.

• Delays: An industry analysis of PHMSA’s proposed regulation and six 

industry stakeholders suggest that use of the purging system could 

delay drivers at fuel terminals, potentially causing backlogs, while 

others said that the purging system will not delay drivers because it 

can operate while drivers are completing necessary final steps before 

leaving a fuel terminal. One industry stakeholder said that the purging 

system would lengthen unloading times, since the system uses the 

truck’s air compressor thereby lowering the pressure available for 

facilitating unloading and slowing unloading speeds. According to 

Cargo Tank Concepts, the system uses very little air, and air that is 

used is replaced quickly by the air compressor and therefore would 

have no impact on unloading.

• Vapor release: Because purging systems use air to push liquid into 

the tank, the systems increase the pressure in the tank. In 2005, the 

California Air Resources Board expressed concern that this increase 

would exceed the tank’s design limit, causing it to vent gasoline vapor 

into the air potentially in violation of emissions limits, a concern 

echoed by one industry stakeholder we interviewed and in nine 

comments submitted in response to PHMSA’s proposed regulation.49

However, according to Cargo Tank Concepts, the increase in air 

pressure is too small to trigger the pressure release valves and cause 

such release.

• Malfunction: Since PHMSA’s proposed rule prohibits wetlines without 

adequate collision protection, in the event of a purging system 

malfunction, a truck would likely not be able to leave a terminal unless 

it could purge its bottom lines. One industry stakeholder was unsure 

 49The American Petroleum Institute, the American Trucking Associations, the Truck Trailer 

Manufacturers Association, the Dangerous Goods Advisory Council, and Baltimore Cargo 

Tank Services referenced the California Air Resources Board’s concerns in their written 

comments.
Page 29 GAO-13-721 Cargo Tank Trucks

how carriers would address the issue of potential malfunction of a 

purging system, but speculated that the truck would have to be offloaded, potentially to another truck or, if the truck was at a fuel 

terminal, via an off-loading station. PHMSA officials said it might be 

possible to create a regulatory exception to allow one-time movement 

of the cargo to its unloading destination or to transfer the cargo to a 

different truck. In either case, the truck with a faulty system could then 

not be reloaded until after the purging system is repaired. Cargo Tank 

Concepts also noted that in the event of a purging system 

malfunction, only the product in the bottom lines would have to be 

removed, not the entire contents of the tank.

• Maintenance: Industry stakeholders agree that the purging system 

would result in additional maintenance and repair costs to the carrier. 

In comments submitted to PHMSA in response to the proposed rule, 

six industry stakeholders expressed concerns about the unknown cost 

of maintenance and repair of the purging system, as well as the 

absence of data on factors such as maintenance, reliability, downtime, and repair and replacement costs. Two industry stakeholders we 

interviewed expressed concern that extreme operating conditions—

very cold or hot climates, for example—could affect the system and 

therefore maintenance costs. However, according to one industry 

stakeholder familiar with the system, issues with the purging system 

are fairly easy to address. Cargo Tank Concepts commented that they 

have sold hundreds of purging systems that are operating reliably and 

incur low maintenance costs.

• Compliance: Four industry stakeholders said that compliance with 

PHMSA’s proposed regulation could be an issue for carriers. One of 

those stakeholders said this could be a particular issue with the 

manual purging system that required drivers to proactively initiate 

purging, as some drivers may forget to initiate the purge, while others 

may skip purging to save time. Additionally, that stakeholder 

suggested that drivers may have a disincentive to purge bottom lines 

if using the vehicle’s compressed air system for that purpose reduced 

the efficiency of other truck operations. Furthermore, according to two 

stakeholders, it could be difficult for carriers or third parties to verify 

compliance, given that some bottom lines lack glass panes that allow 

visual verification of the amount of liquid present in the bottom line. 

PHMSA officials did not view this as a major concern and told us that 

regulatory compliance cannot always be fully monitored. PHMSA also 

noted that carriers could choose other methods of eliminating wetlines 

besides the purging system.
Page 30 GAO-13-721 Cargo Tank Trucks

Stakeholders identified other options to address wetline safety risks in 

addition to the purging system. However, none of the other options are in 

use by the industry and many are hypothetical, making it is difficult to 

assess their costs, benefits, and feasibility. DOT summarized a number of 

options to address wetline safety risks in a 1999 preliminary cost-benefit 

analysis, but additional information about options other than the purging 

system was limited to propositions and conjecture.50 Therefore, we relied 

on views from industry and safety stakeholders to determine the 

advantages and disadvantages of each option. Table 2 summarizes 

options and key advantages and disadvantages as identified by 

stakeholders.

Table 2: Stakeholders’ Views on Options to Address Wetline Risks

Options Description Advantages Disadvantages

Purging system 

installed on the 

cargo tank truck

After loading, system 

introduces compressed air 

from an auxiliary tank into the 

wetlines under low pressure, 

pushing liquid from the 

wetlines into the cargo tank 

body. 

Eliminates all but trace 

amounts of fuel from bottom 

lines.

May detect internal valve 

leaks.

Retrofit feasible.

Currently in use.

If malfunctioning, other measures would be needed 

to empty wetlines.

Driver compliance with manual system difficult for 

carriers to enforce.

Opinions varied on consequences of low 

pressurization of an unpressurized tank.

Significant concern from industry over dangers of 

welding work needed for this option if DOT were to 

require retrofitting.

Purging system 

installed at the 

loading terminals

After loading, the driver would 

connect to a stationary 

purging system. The system 

would then introduce air into 

the wetlines, forcing liquid 

from the wetlines into the 

cargo tank body.

Eliminates all but trace 

amounts of fuel from bottom 

lines.

May help detect leaks in 

cargo tank internal 

emergency valves.

Retrofit feasible.

Adds to time the driver spends at the terminal.

Difficult for carriers to enforce.

Requires modification to both trucks and terminals.

Short loading 

lines

Shorter loading lines are 

added to tank trucks so that 

bottom lines are used only for 

unloading.

Reduces the amount of liquid 

in external lines.

Lines would not be exposed 

to damage in the event of a 

rollover.

Retrofit infeasible.

Greater distance between loading heads would 

necessitate modifications to either the loading rack

or loading procedure, raising some cost and safety 

concerns.

 50U.S. Department of Transportation, Research and Special Programs Administration, 

Risk / Benefit-Cost Analysis, Prohibiting Hazardous Material in External Piping of MC 

306 / DOT 406 Cargo Tank Motor Vehicles: Preliminary Assessment (Washington, D.C.: 

1999).

Other Options to Address 

Wetline Safety Risks Are 

Not in Use, and Many Are 

Hypothetical
Page 31 GAO-13-721 Cargo Tank Trucks

Options Description Advantages Disadvantages

Internal lines The horizontal components of 

bottom lines would be placed 

on the inside of tank 

compartments.

Eliminates liquid in external 

lines.

Minimizes exposed elements

Retrofit infeasible.

Loading line leaks would no longer be visible and 

may contaminate liquid.

Double-closing 

stop valve

Upon collision, a self-closing 

stop valve would protect 

against cargo tank spills while 

other closures would seal 

wetline ends.

Reduces risk that designedto-fail shear point will result in 

flammable liquid spill.

Retrofit feasible.

Does not eliminate wetlines.

Stop valve could be damaged in the event of a 

collision.

To reduce wetline risk further would require 

stronger pipes, like the protection of tanks for 

trucks carrying propane.

Top loading Cargo tank trucks would be 

loaded from the top of the 

tank.

Eliminates liquid in external 

lines.

Modifications necessary to meet vapor recovery 

requirements, address issues of worker safety.

Requires reconfiguration of loading racks.

Draining wetlines 

at the terminal

After loading the truck and 

closing the valves the carrier 

would reconnect to a tank 

(either at the rack or 

elsewhere in the terminal) and 

drain the liquid in the bottom 

lines.

Eliminates liquid in external 

lines.

Terminals currently have 

storage tanks for “slop.”

Terminals would need new administrative 

processes, revised automated metering, and 

additional storage—possibly separate storage unit 

for each liquid.

Mixing products would inhibit resale; if unable to be 

sold, would create hazardous waste. 

Guards, shields, 

or under-ride 

protection

Cargo tank trucks would be 

equipped with bottom damage 

protection devices.

Reduces risk of wetline 

rupture.

Does not eliminate wetlines.

Retrofit inadvisable, possibly infeasible.

Added weight of guards would reduce the carrying 

capacity of tank trucks.

In a collision, the guards could puncture the tank or 

transfer force and cause the tank to rupture.

Guards to prevent pedestrian and bicycle underrides would not sufficiently protect the tank.

Source: GAO analysis of documents from DOT’s 2004 and 2011 proposed regulations to address wetline safety risk, as well as 

interviews with PHMSA, NTSB, Cargo Tank Concepts, industry stakeholders, and safety groups.

For all the options, the most obvious advantage is the potential to address 

wetline safety risks, but according to stakeholders, the extent that these 

options address those risks varies. Some options would leave traces of 

fuel in the cargo tank trucks’ bottom lines, while others would retain 

wetlines but potentially reduce risk by shielding them or altering wetline 

design to minimize spillage in the event of a collision.

Some stakeholders’ concerns with the wetline purging system apply to 

other options as well, such as concerns about the safety of retrofitting 

cargo tank trucks. For at least three of the other options, retrofits are 

either not feasible or inadvisable, which would mean these options could 

only be implemented on new tank trucks, delaying safety benefits. In 
Page 32 GAO-13-721 Cargo Tank Trucks

addition, the entity that would bear the initial cost of implementation varies 

among the options. For example, one stakeholder said that carriers would 

bear the initial cost of installing side-guards on tank trucks to shield them 

from collisions, since that option would require changes to the cargo tank 

design. In contrast, short loading lines that would replace the longer 

bottom lines for loading tanks could require changes to the cargo tank 

design and modifications to the loading rack, so the carriers and the fuel 

terminals would both incur initial costs. Stakeholders suggested that other 

agencies, such as the Environmental Protection Agency or the 

Occupational Safety and Health Administration, may need to be consulted 

on the design and implementation of some options due to potential 

environmental and/or worker-safety concerns.

In January 2011, PHMSA issued a notice of proposed rulemaking to 

prohibit the transport of flammable liquid in the bottom lines of cargo tank 

trucks unless the vehicle is equipped with bottom damage protection 

devices, along with an analysis of the proposal’s costs and benefits. In 

March 2012, PHMSA updated the assumptions of its cost-benefit analysis 

in response to comments submitted by stakeholders in the rulemaking 

and also changed its methodology (for discussion of the changed 

methodology, see app. II). We reviewed the assumptions and 

methodology in the March 2012 working draft document because they 

reflected PHMSA’s more current thinking; however, this document was 

provided in draft form and has not been released publicly. PHMSA has 

not issued a final rule on this subject; therefore, information in either the 

2011 or 2012 analysis is subject to change. PHMSA officials told us they 

ceased all work on the rulemaking in response to the MAP-21 

requirement that PHMSA not issue a final rule pending the completion of 

our study. PHMSA may, however, issue a rule earlier if it determines that 

a risk to public safety, property, or the environment is present or an 

PHMSA Analyzed 

Costs and Benefits for 

a Proposed Wetlines 

Rule, but 

Uncertainties Limit 

the Usefulness of the 

Analysis

PHMSA Proposed a Rule 

to Address Wetline Safety 

Risks and Analyzed 

Associated Costs and 

Benefits
Page 33 GAO-13-721 Cargo Tank Trucks

imminent hazard exists and that the regulation will address the risk or 

hazard.

PHMSA based its cost-benefit analysis on the assumption that the 

industry would comply with the proposed rule by installing a wetline 

purging system on cargo tank trucks—specifically the manual version of 

the system offered by Cargo Tank Concepts.51

PHMSA’s 2011 analysis found that costs exceeded benefits in all of the 

compliance scenarios, while the 2012 analysis concluded that benefits 

exceeded costs on a present value basis by about $2 million in the 20-

year scenario; but costs exceeded benefits in the three scenarios with 

shorter compliance time frames. Table 3 describes the costs and benefits 

considered in the analysis.

PHMSA’s analysis 

included multiple compliance scenarios that varied in the amount of time 

the industry would have to comply with the rule. The longest scenario 

called for compliance within 20 years, which, given PHMSA’s assumption 

that tank trucks have a 20-year life, would mean the device could be 

installed on only new trucks and no retrofitting would be needed. The 

shortest scenario called for compliance within 5 years and assumed the 

industry would retrofit many of its existing tank trucks concurrently with a 

truck’s required 5-year inspection, at which time PHMSA officials told us 

trucks are cleaned of gasoline and vapor as part of the inspection 

process, reducing the risk of explosion from welding on an existing tank.

 51Although the proposed rule states compliance could be achieved by installing specified 

types of bottom damage protection, stakeholders told us this option is possibly infeasible 

and retrofits would be inadvisable for tank trucks (see previous table 2). PHMSA’s costbenefit analysis does not consider costs and benefits of bottom protection as a 

compliance option.
Page 34 GAO-13-721 Cargo Tank Trucks

Table 3: Costs and Benefits Included in PHMSA’s 2011 Cost-Benefit Analysis and Its 2012 Draft Revision

Costs Benefits

• Purchase and installation of manual wetline 

purging systems on all cargo tank trucks.

• Annual maintenance of purging systems.

• Weight penalty, resulting from the reduced 

carrying capacity of a tank truck to account 

for the weight of the purging system.a

• For the 2012 analysis, PHMSA also included 

additional operating costs that carriers would 

incur to transport product displaced by the 

added weight of the purging system.

• Avoidance of all wetline incidents, including 

associated fatalities, product loss, clean-up costs, 

carrier damage, and property damage. (The 2011 

analysis also included evacuation delays, but this 

was removed in the 2012 analysis.)

• Avoidance of associated consequences, such as 

traffic delays and risk to emergency responders.

• Avoidance of a low-probability, high-consequence 

event such as the 1997 Yonkers incident.

Source: GAO analysis of PHMSA’s 2011 cost-benefit analysis and 2012 working draft cost-benefit analysis.

a

Federal regulation limits the weight of commercial vehicles on the interstate highway system, see 23 

C.F.R. part 658. In general, off the interstate highway system, states may set their own commercial 

vehicle weight standards. Therefore, the added weight of a purging system could result in decreased 

product carrying capacity.

PHMSA withdrew a previous proposed wetlines rule in 2006 because it 

determined that the rule’s potential benefits did not justify its costs. The 

agency issued its more recent proposal in 2011 because the agency still 

views preventing wetline incidents as an important safety issue and, 

according to PHMSA officials, given further development of the wetline 

purging system, preventing wetline incidents can now be done in a 

manner that is cost-beneficial. In contrast, 11 of the 12 industry 

stakeholders we spoke with opposed the proposed rule for reasons such 

as their belief that wetlines are not a major safety issue and their 

concerns about the possible solutions, which were previously discussed 

in this report.52

 52One industry stakeholder, a petroleum marketer and carrier that uses the wetline 

purging system, told us it has no position on the proposed regulation.

Six of the 10 safety stakeholders we interviewed 

supported the rule, while three others took no position. Four other safety 

groups we contacted declined to be interviewed because they had no 

position on the issue.
Page 35 GAO-13-721 Cargo Tank Trucks

OMB has issued guidance for agencies engaged in rulemaking on the 

use of data and treatment of uncertainty in cost-benefit analysis.53

PHMSA’s calculated benefits are based on the assumption that use of the 

purging system by tank truck carriers will prevent all wetline incidents; the 

value of this benefit is based on PHMSA’s analysis of its past incident 

data to identify wetline incidents and their associated consequences. 

Other assumptions in the analysis are based on testimonial information 

and observation, rather than market data. Specifically, cost calculations 

are based on information from the purging system’s manufacturer 

regarding the purchase and installation costs of the technology. 

Additionally, information about purging system performance—an input 

that can affect both benefits and costs—is based on 1) information from 

the manufacturer, 2) anecdotal information about the performance of the 

technology provided by the major carrier that is using the automatic 

version of the system, and 3) PHMSA’s observation of a prototype 

version of the manual purging system that shows how the technology 

works but is not actually installed on a tank truck. Although PHMSA 

included sensitivity analyses in its 2011 and 2012 cost-benefit analyses to 

account for some uncertainties, issues with the data and assumptions 

The 

guidance states that market data is a rich source of information, and that 

estimating cost when active markets do not exist is more difficult, 

requiring appropriate proxies. Accordingly, an agency should discuss the 

quality of available data used and in the absence of adequate data, the 

agency will need to make certain assumptions. With regard to uncertainty, 

the guidance states that estimates of benefits and costs are typically 

uncertain because of imprecision in underlying data and assumptions. 

Because uncertainty is common when conducting cost-benefit analysis, 

OMB states that the effects of uncertainty should be analyzed and 

reported. To address plausible changes in the assumptions and numeric 

inputs of a cost-benefit analysis, OMB recommends that agencies 

consider providing a sensitivity analysis to show how the results of the 

analysis might vary to account for such uncertainty. Limitations of the 

analysis because of uncertainty or biases surrounding data or 

assumptions should, according to OMB, be discussed. Additionally, the 

OMB guidance provides that when uncertainty has significant effects on 

the final conclusion about net benefits, the agency should consider 

additional research prior to rulemaking.

 53Office of Management and Budget, Guidelines and Discount Rates for Benefit Cost 

Analysis of Federal Programs, OMB Circular A-94, (revised 1992), and Regulatory 

Analysis, OMB Circular A-4, (Sept. 17, 2003).

Uncertainty Associated 

with Aspects of PHMSA’s 

Cost-Benefit Analysis 

Limits Its Usefulness for 

Supporting the Proposed 

Rule
Page 36 GAO-13-721 Cargo Tank Trucks

that can affect costs and benefits were not addressed through sensitivity 

analysis.54

PHMSA’s analysis assumes a cost of $2,300 to equip each new or 

existing cargo tank truck with a manual wetline purging system, plus the 

cost of installation labor, rather than the higher cost of the automatic 

version currently used, which the manufacturer sells for $3,800 or $3,950 

depending on the size of the tank truck.

Consequently, some costs and benefits in the analysis may be 

more uncertain than PHMSA has accounted for.

55

Were the proposed rule issued, such action would likely generate 

demand for the purging technology, which could have several effects. 

Specifically, it could enable the product to be produced at a lower cost 

due to achieving economies of scale related to a higher level of 

production, and it could also attract more companies into the market to 

produce alternative purging systems. Although we are aware of only one 

company offering purging system technology at the time of our review, at 

PHMSA assumed companies 

would opt for the manual system because of its lower cost and used that 

as the cost basis in its analysis. As previously discussed, there are no 

manual systems in use to date, and some industry stakeholders 

suggested that carriers may prefer the automatic system for compliance 

and simplicity reasons, despite its higher cost. Thus, although there is a 

limited market for the automatic purging system, the lack of market use to 

date for the manual system makes the cost of compliance with the 

regulation uncertain despite a stated price from the manufacturer.

 54PHMSA included sensitivity analyses to test how costs and benefits could differ if certain 

of the assumptions were changed. In the 2011 sensitivity analysis, costs were tested with 

alternative assumptions of a lower purging system installation cost and no additional costs 

related to the weight of the purging unit, assumptions which lowered the proposed rule’s 

cost. Costs were also tested with an assumption of a greater number of equipped trucks, 

an assumption that would increase cost. Additionally, benefits were tested under an 

alternative assumption of a higher number of avoided fatalities and other damages—

changes that would increase the proposed rule’s benefit. The 2012 analysis included two 

sensitivity calculations: a “bunching” analysis, which assumed carriers would equip their 

trucks with the technology as late as possible to meet the compliance deadline, and an 

alternative assumption about the price of the purging system being lower than assumed in 

the base case, due to the manufacturer’s reduction in the price of the manual wetline 

purging system.

55PHMSA used the $2,300 cost because it was the price Cargo Tank Concepts offered 

the manual purging system at until the company more recently dropped its listed price to 

$1,380. PHMSA’s draft 2012 analysis acknowledges the price drop and included a 

sensitivity analysis to test the effect of a lower-cost purging system. PHMSA officials told 

us they did the calculations with the higher value to be more conservative.

Cost Assumptions
Page 37 GAO-13-721 Cargo Tank Trucks

least three patents for other purging systems have been granted, making 

industry competition a possibility. Consequently, in the absence of 

market-based information for the manual purging system, it is difficult to 

develop assumptions on the cost of the technology for the cost-benefit

analysis. While these factors could have an impact on the sales price of 

the unit, PHMSA’s analysis does not fully account for these cost 

uncertainties and, to the extent that market information exists for the 

automatic purging system, such information is not used to support costs 

in the analysis. PHMSA’s analysis presents a sensitivity analysis only for 

a lower cost of the purging system on the basis that a more competitive 

market could develop if its proposed rule were finalized and that the 

manufacturer recently began offering the manual purging system at a 

lower price.

Additionally, stakeholders we spoke with mentioned a number of other 

cost-related concerns:

• Installation approach. As previously discussed, stakeholders raised 

safety concerns about potential welded retrofitting needed to install 

purging systems under the shorter compliance scenarios, due to the 

risk of explosion if cargo tanks are not thoroughly de-gassed. Safety 

measures to address these concerns could add additional cost. 

However, PHMSA’s analysis addressed these concerns by stating 

that carriers could install nonwelded purging systems. PHMSA 

officials also told us that because the compliance scenarios were 

created with 5-year intervals, retrofitting could occur concurrently with 

5-year inspections when tanks are normally cleared of flammable 

product and vapor. PHMSA officials also stated that there are 

procedures to de-gas tanks to make them safe for such work.

• Installation time. PHMSA’s analysis does not include the cost of 

down-time to install the purging system, even for scenarios requiring 

retrofitting because the analysis assumes the work can be done 

concurrently with routine inspections. However, stakeholders reported 

a range of time needed to install a purging system, which could take 

longer than the inspections; thus it is unclear that the inspection and 

retrofitting could actually be done simultaneously.

• Maintenance. PHMSA assumes maintenance on a purging system will 

cost $3 per year per truck, based on an assumption about the cost of 

inspecting the device every 5 years. Stakeholders with experience 

using the technology said this cost is too low and told us the 

technology required occasional repairs or replacement. According to 

PHMSA’s analysis, it includes a low-cost maintenance estimate 
Page 38 GAO-13-721 Cargo Tank Trucks

because it states that pneumatic technologies like the purging system 

require very little maintenance because they have few moving parts 

that can fail.

We also found uncertainty in PHMSA’s data and assumptions related to 

benefits:

• Fatalities. As previously discussed, we identified inaccuracies in 

PHMSA’s analysis regarding the number of fatalities that could be 

avoided by the proposed wetlines rule, and PHMSA did not include a 

sensitivity analysis to account for its rule potentially preventing fewer 

deaths than assumed in its cost-benefit analysis. Both the 2011 and 

2012 cost-benefit analyses stated there were 4 incidents with hazmatrelated fatalities during the incident study period (resulting in 5 

fatalities).56 After discussing the inaccuracies with PHMSA officials, 

they agreed it would be more accurate for their analysis to reflect 4 

fatalities occurring from 3 fatal wetline incidents. Questions over 

PHMSA’s wetline fatality analysis have been raised before. In a 2001 

letter critiquing a prior wetlines proposed rule, OMB encouraged DOT 

to more fully address the uncertainty in the cause of fatalities in its 

wetlines cost-benefit analysis, specifically to address uncertainty with 

whether fatalities might be caused by factors other than the release of 

hazardous materials and would therefore not be avoided by a rule 

addressing wetlines.

Because fatalities are a major contributor to the calculated value of 

the benefits of the regulation, a reduction of even one fatality in the 

analysis could have significant impact on the amount of calculated 

benefits for the proposed rule.57

 56Although there were additional wetline incidents during this period with fatalities, those 

fatalities were attributed to causes other than the release of hazmat, such as blunt force 

trauma, and thus are not counted as contributing to the benefits of the proposed wetline 

rule.

For example, PHMSA’s 2012 

analysis concluded that with 4 fatal incidents during the study period 

and an average of 1.67 people per vehicle, the proposed rule would 

57For calculating the benefits of proposed rules that seek to prevent the loss of life, DOT 

uses a value of statistical life that seeks to represent the benefit of preventing a fatality. 

Specifically, the statistical value of one life is the amount that society is willing to pay for a 

safety improvement that would prevent one fatality. PHMSA’s draft 2012 analysis used a 

value of $6.2 million that DOT set in 2011. More recently, in 2013, DOT revised the value 

of statistical life to be $9.1 million in 2012 dollars.
Page 39 GAO-13-721 Cargo Tank Trucks

avoid 6.7 fatalities for a benefit of about $3.4 million per year.58 Were 

the analysis recalculated with 3 fatal incidents, the annual benefit of 

avoided fatalities would be about $2.5 million per year, about $1 

million less. This is significant, given that avoided fatalities comprise 

more than half of the almost $6.5 million total annual benefit of the 

proposed rule. In the 2012 draft cost-benefit analysis, PHMSA’s 20-

year compliance scenario showed a total net benefit of about $2 

million, which was the only scenario where benefits exceeded costs. 

Thus, while PHMSA has not issued a final rule on this subject and 

information in either the 2011 or draft 2012 analysis is subject to 

change, had the analysis been calculated with one less fatal incident, 

costs would have exceeded benefits in that scenario as well.

• Effectiveness. PHMSA’s analysis assumes its proposed rule would 

prevent all wetline incidents, implying that the purging systems 

installed to prevent these incidents would be 100 percent effective. 

However, PHMSA’s analysis does not acknowledge that the system 

may malfunction, may not prevent wetline incidents due to certain 

intervening factors, and that the system may not always be used as 

intended. We are aware of two wetline incidents that have occurred 

since 2008 involving trucks equipped with an automatic wetline 

purging system. According to the carrier involved in both incidents, in 

one instance, the driver had turned off the system and, in the other, a 

problem with the lining of the cargo tank prevented the system from 

functioning properly. Based on this information, it does not appear 

there was a functional problem with the purging device in either 

instance; however, wetline incidents occurred nonetheless.

• Most Catastrophic Incident. PHMSA’s 2011 and 2012 analyses 

included additional benefits from avoiding a low-probability, highconsequence event like the 1997 Yonkers incident. Even though the 

Yonkers incident occurred prior to the years for which data were used 

for the primary analysis of expected benefits, this incident was 

included in the analysis—meaning that it comprised a portion of the 

 58In the 2011 analysis, avoided fatalities were about $3.9 million of the more than $7.7 

million in annual expected consequences and would also be about $1 million less per year 

if calculated with one less fatal incident. Figures are in 2009 dollars. The numbers of 

fatalities and fatal incidents did not change between the 2011 and 2012 versions of the 

cost-benefit analysis. Because the 2012 analysis covered a longer period of time, the 

benefit per year of avoided fatalities was lower in the updated analysis. PHMSA’s 

assumptions about the number of passengers per car and the statistical value of a life 

were also slightly different in both analyses.
Page 40 GAO-13-721 Cargo Tank Trucks

expected benefits due to accidents avoided—under the assumption 

that a severe incident such as this would happen very infrequently. 

Specifically, in both of these analyses, the expected benefits of 

avoiding an incident of this level of consequence were allocated over 

a 20-year period—meaning that the agency assumed such a 

catastrophic incident could be expected to occur once every 20 years. 

PHMSA officials told us they considered allocating the benefits over a 

longer 40-year period in response to industry criticism that there has 

been only one such extraordinary incident on record but that the 

agency has not reached a final decision on this issue. When assumed 

to be a 20-year event, the expected benefits of avoiding a Yonkerslike incident in the 2012 benefit cost analysis comprise about 1/3 of 

the proposed rule’s benefits. Given the apparent rarity of such an 

incident, it is uncertain whether 20 years, 40 years, or some other 

time period is an appropriate assumption of the frequency of such an 

event. However, PHMSA did not account for this uncertainty in a 

sensitivity analysis.

Wetline incidents have ranged from minor incidents to serious accidents 

that have claimed lives and damaged property. Because PHMSA does 

not specifically provide an option to indicate a wetline incident on its 

incident reporting form, it is difficult to identify the number of wetline 

incidents from PHMSA’s incident data. Additionally, due to inaccuracies in 

the data, the magnitude of the risk they pose to safety is also unclear. 

Although PHMSA has made changes to improve the quality of its incident 

data, the concerns we identified call into question the data’s usefulness 

for characterizing key aspects of the benefits of avoiding these incidents,

particularly the extent to which a wetlines rule would prevent fatalities. 

Furthermore, PHMSA’s economic analysis does not account for these 

limitations. Thus, the analysis does not adequately convey the uncertainty 

of PHMSA’s calculated benefit of the rule. Furthermore, PHMSA’s 

analysis has not adequately addressed the market uncertainty with regard 

to the cost of the purging system, given that it is in limited use and the 

particular version of the system assumed in the analysis, to date, has not 

been in use.

While NTSB has called on PHMSA to address wetline risks, industry 

stakeholders have raised concerns about PHMSA’s proposed regulation, 

particularly given that they view wetline incidents as occurring infrequently 

and that there could be other safety risks with the assumed option to 

address wetline safety risks. Without adjusting its cost-benefit analysis to 

account for the uncertainties due to the limited market for the purging 

system and limitations with PHMSA’s incident data, the consequences of 

Conclusions
Page 41 GAO-13-721 Cargo Tank Trucks

wetline incidents remain unclear and the costs and benefits of wetline 

regulation may not be accurately calculated in PHMSA’s regulatory 

analysis.

To improve the reliability of data used to identify wetline incidents, we 

recommend that the Secretary of Transportation direct the Administrator 

of PHMSA to take the following two actions:

• Revise incident reporting to better capture wetline incidents and their 

consequences, such as by requiring specific reporting of wetline 

incidents by modifying the reporting form to include a specific indicator 

of such incidents, and adjusting the incident reporting form to indicate 

whether there are minimal costs versus no costs when costs are 

below the $500 reporting threshold.

• Address limitations with the accuracy and completeness of 

information used to assess the impact of wetline incidents, such as by 

specifying circumstances when PHMSA should seek missing cause 

and cost information, and potentially using sources other than the 

carrier to acquire information (such as investigations by local law 

enforcement or other federal agencies), particularly for the most 

severe incidents for which having accurate incident information is 

critical to oversight.

To strengthen the agency’s rulemaking analysis, we recommend that the 

Secretary of Transportation direct the Administrator of PHMSA to take the 

following action:

• Strengthen the regulatory assessment of the proposed wetline rule’s 

costs and benefits to better address the uncertainty of underlying

factors. Such action could include incorporating more real-world 

information about purging systems or, if considered, other wetline 

solutions, and conducting additional sensitivity analyses for areas of 

uncertainty that are not addressed by improved data collection.

We provided a draft of this report to the Department of Transportation for 

review and comment. DOT indicated that PHMSA would take this report 

into consideration as it continues to consider rulemaking and works to 

improve its incident data collection and internal review procedures. The 

department did not agree or disagree with our recommendations, but 

provided technical comments that we incorporated as appropriate.

Recommendations for 

Executive Action

Agency Comments
Page 42 GAO-13-721 Cargo Tank Trucks

We are sending copies of this report to the appropriate congressional 

committees, the Secretary of Transportation, and other interested parties. 

In addition, the report is available at no charge on the GAO website at 

http://www.gao.gov.

If you or your staff have any questions about this report, please contact 

me at (202) 512-2834 or flemings@gao.gov. Contact points for our 

Offices of Congressional Relations and Public Affairs may be found on 

the last page of this report. GAO staff who made key contributions to this 

report are listed in appendix III.

Susan A. Fleming

Director, Physical Infrastructure Issues
Appendix I: Objectives, Scope, and 

Methodology

Page 43 GAO-13-721 Cargo Tank Trucks

This report discusses (1) the extent that the Pipeline and Hazardous 

Materials Safety Administration’s (PHMSA) data can be used to reliably 

identify wetline safety risks, (2) options for addressing wetline safety risks, 

and (3) how well PHMSA has assessed the costs and benefits of 

addressing these risks through regulation.

To evaluate the extent that PHMSA’s data reliably capture wetline 

incidents, we examined PHMSA’s process for identifying wetline incidents 

and the data for the incidents that the agency has identified as being 

wetline-related occurring from the beginning of January 1999 to the end 

of March 2011. Our evaluation assessed PHMSA’s efforts against federal 

internal control standards that require agencies to have relevant, reliable, 

and timely information for decision-making and external reporting 

purposes, and Office of Management and Budget (OMB) data quality 

guidelines for regulatory purposes.1 Specifically, we analyzed the 

narrative information for these incidents to determine how useful this 

information is for identifying the incidents as being wetline-related. We 

examined the extent to which the incidents’ coding of the component of 

the tank truck that failed could be indicative of a wetline incident. We also 

examined the extent to which these data accurately reported information 

about incident fatalities and to what extent they reported information 

about other incident damages. We selected 12 incidents to review as 

case studies to learn more about PHMSA’s process for recording 

information about these incidents and to look for potential irregularities 

between PHMSA’s database and other available information about the 

incidents. We selected these incidents to span the 1999 to 2011 time 

frame, to represent a range of minor to major incidents as measured by 

reported fatalities and other damages, and to include any incidents that 

were investigated by PHMSA or the National Transportation Safety Board 

(NTSB). We also included two incidents that PHMSA had determined to 

be wetline-related in its 2011 analysis but later determined not to be 

wetline incidents in its draft 2012 analysis.2

 1

GAO, Standards for Internal Control in the Federal Government,

We reviewed the reliability of 

GAO/AIMD-00-21.3.1 

(Washington, D.C.: November 1999); and Office of Management and Budget, Regulatory 

Analysis, OMB Circular No. A-4 (Sept. 17, 2003). 

2

For its January 2011 cost-benefit analysis, PHMSA identified wetline incidents occurring 

between January 1999 and December 2008. For its updated draft March 2012 

assessment, PHMSA expanded its analysis to incidents occurring as of March 2011 and, 

in doing so, added some incidents to its list of wetline incidents but also removed some 

incidents in response to comments from stakeholders that questioned whether some of 

the incidents from the 2011 analysis were actually wetline incidents.

Appendix I: Objectives, Scope, and 

Methodology

Objectives

Scope and 

Methodology
Appendix I: Objectives, Scope, and 

Methodology

Page 44 GAO-13-721 Cargo Tank Trucks

these incident data by examining them for missing data and 

inconsistencies, reviewing PHMSA’s process for obtaining wetline data 

and maintaining them in the agency’s database, and related internal 

controls. We concluded that the data were sufficiently reliable for the 

purposes of our report. Our conclusion that PHMSA’s incident data are 

not sufficiently reliable for use in its regulatory analysis is independent of 

our conclusion that the data are sufficiently reliable for our purpose, since 

our purpose was to assess to what extent the data reliably identify wetline 

incidents and their characteristics. Based on the information PHMSA 

provided about how it uses these data for this purpose and the availability 

of PHMSA’s incident data through its online incident database, we were 

able to make this assessment. We reviewed documents on and 

interviewed PHMSA officials about the agency’s prior and ongoing efforts 

to improve the quality of its hazmat incident data.3

To describe options to address wetline safety risks, we reviewed 

documentation from PHMSA’s current and most recent prior related 

rulemaking efforts to identify what options have been proposed to 

address wetline safety risks and which major safety and industry 

stakeholders have been engaged on this issue. For contextual 

information about the feasibility of these options, we also visited a fuel 

terminal where cargo tank trucks are loaded. We reviewed documents 

from and interviewed associations and experts representing safety 

advocacy and various components of industry involved in the 

transportation of flammable liquids to understand stakeholder views on 

the options to address wetline safety risks. Specific stakeholders we 

interviewed are listed in table 4.

Since our review 

focuses specifically on the issue of wetlines, we did not assess PHMSA’s 

progress in improving its hazardous materials incident data in general.

 3

During the course of our review, PHMSA officials told us they were involved in ongoing 

efforts to improve their incident data pursuant to deficiencies the agency had previously 

identified and hazardous material transportation incident data requirements in MAP-21. 

Consequently, we were not able to fully assess how these improvement efforts might 

affect their wetline incident data.
Appendix I: Objectives, Scope, and 

Methodology

Page 45 GAO-13-721 Cargo Tank Trucks

Table 4: Wetline Industry and Safety Stakeholders Interviewed

Industry stakeholder (segment) Safety stakeholder (segment)a

• American Petroleum Institute (oil and natural 

gas industry)

• American Trucking Associations (trucking 

industry)

• Baltimore Cargo Tank Services (tank truck repair 

and service company)

• Dangerous Goods Advisory Council (hazardous 

materials transportation safety organization)

• Independent Fuel Terminal Operators 

Association (terminals for distributing flammable 

liquid products)

• International Liquid Terminals Association 

(terminals for distributing flammable and other 

liquid products)

• National Tank Truck Carriers (tank truck carriers)

• Petroleum Marketers Association of American 

(petroleum marketing trade associations)

• Renewable Fuels Association (ethanol 

producers)

• Society of Independent Gasoline Marketers of 

America (marketers of petroleum products)

• Sunoco (petroleum marketer, carrier, and 

terminal operator)

• Truck Trailer Manufacturers Association 

(tank truck manufacturers)

• Advocates for Highway and Auto Safety 

(consumer, health, safety, and insurance alliance)

• Bob Chipkevich (transportation safety consultant)

• Commercial Vehicle Safety Alliance (association of 

government motor carrier safety officials)

• International Association of Fire Chiefs (emergency 

response officials)

• International Brotherhood of Teamsters 

(labor union)

• Joe Connelly (hazardous materials safety 

consultant)

• National Association of State Fire Marshals 

(state fire response officials)

• National Board of Boiler and Pressure Vessel 

Inspectorsb (tank inspection, safety, training and 

standards)

• NTSB (federal incident investigation)

c

• Truck Safety Coalition (public safety)

Source: GAO.

a

We contacted four other safety organizations that declined to be interviewed because they were not 

actively working on or did not have a position on the issue of wetline safety. These were American 

Association of Motor Vehicle Administrators, American Association of State Highway and 

Transportation Officials, Governors Highway Safety Association, and Insurance Institute for Highway 

Safety.

b

We requested an interview with the National Board of Boiler and Pressure Vessel Inspectors, which 

instead provided written answers to our questions.

c

Although NTSB is a government agency, in the context of this engagement we considered it a safety 

stakeholder due to its expertise having investigated wetline incidents and its recommendation that 

DOT prohibit wetlines.
Appendix I: Objectives, Scope, and 

Methodology

Page 46 GAO-13-721 Cargo Tank Trucks

We placed particular focus on examining the wetline purging system, 

since it is the option used in PHMSA’s wetlines rulemaking analysis and 

the only option we are aware of that has been installed to address wetline 

risks. To better describe this option, we reviewed documentation about 

the system and interviewed the system manufacturer, Cargo Tank 

Concepts. We also interviewed stakeholders with direct experience with 

the system. We interviewed Sunoco—a petroleum marketer, carrier, and 

terminal operator that has installed the system on its tank truck fleet—and 

visited a Sunoco terminal near Philadelphia, Pennsylvania, that 

distributes flammable liquid products to tank trucks equipped with the 

purging system. We also interviewed Baltimore Cargo Tank Services, a 

tank service company that has installed the system on tank trucks. Based 

on reviews of patent applications and an industry trade publication, we 

identified other companies that may be able to produce similar wetline 

purging technology and interviewed two of them: Civacon and Franklin 

Fueling Systems.

Because most of the options to address wetline safety risks are 

theoretical—and the one solution that has been implemented is not 

widespread—our ability to present specific information about solutions’

costs and benefits was limited. Instead, we focused on identifying to what 

extent stakeholders agree or disagree on information about these options, 

including the feasibility of implementing them in the current operating 

environment.

To evaluate how well PHMSA has assessed the costs and benefits of 

addressing wetline risks through regulation, we reviewed prior 

Department of Transportation rulemakings on wetlines to understand the 

history of the agency’s work on this issue and focused our analysis on the 

current proposed rule, beginning with the Notice of Proposed Rulemaking 

that PHMSA issued in January 2011. We analyzed PHMSA’s January 

2011 cost-benefit analysis and an updated working draft version of the 

analysis from March 2012. We reviewed PHMSA’s process and 

assumptions used for developing these analyses and the reasons for 

changes between them. We reviewed comments in the rulemaking record 

and interviewed stakeholders about their views on PHMSA’s efforts to 

address wetline safety risks. We assessed PHMSA’s efforts against OMB 

guidance for use of data and cost-benefit analysis to support rulemaking.4

 4

Office of Management and Budget, Guidelines and Discount Rates for Benefit Cost 

Analysis of Federal Programs, OMB Circular A-94, (revised 1992), and Regulatory 

Analysis, OMB Circular A-4, (Sept. 17, 2003).
Appendix I: Objectives, Scope, and 

Methodology

Page 47 GAO-13-721 Cargo Tank Trucks

We also reviewed PHMSA’s non-regulatory efforts to address wetline 

safety risks, which consisted of an effort to raise awareness of emergency 

responders, following the agency’s withdrawal of its most recent prior 

proposed rule in 2006.

We conducted this performance audit from September 2012 to 

September 2013 in accordance with generally accepted government 

auditing standards. Those standards require that we plan and perform the 

audit to obtain sufficient, appropriate evidence to provide a reasonable 

basis for our findings and conclusions based on our audit objectives. We 

believe that the evidence obtained provides a reasonable basis for our 

findings and conclusions based on our audit objectives.
Appendix II: PHMSA’s Wetline Proposed-Rule 

Cost-Benefit Methodology and Related 

Changes

Page 48 GAO-13-721 Cargo Tank Trucks

To support its proposed wetline rule, PHMSA developed analyses of the 

rule’s costs and benefits: PHMSA released a first analysis with the 

proposed rule in January 2011 and provided us a working draft of an 

updated analysis from March 2012 that the agency did not release 

publicly. In updating its cost-benefit analysis in 2012, PHMSA made 

several changes to its methodology for calculating costs and benefits that 

affect the outcomes of the analysis and may affect the ability to compare 

its scenarios.

Both the 2011 and 2012 analyses are built on the assumption that tank 

trucks have a useful life of 20 years. Therefore, the entire tank truck fleet 

in existence at the time of a rule’s effective date would presumably be 

replaced during the course of the 20 years that followed. The 2011 and 

draft 2012 analyses include four alternative scenarios with varying time 

periods for achieving compliance with the proposed rule—specifically in 5, 

10, 15, or 20 years. Were a rule to require compliance within 20 years, 

carriers could achieve compliance by equipping only new trucks with a

wetline purging system. If compliance were required sooner, some 

degree of retrofitting of existing tank trucks would be required, in addition 

to equipping any vehicles that are new in the compliance timeframe.

All four scenarios in the 2011 analysis were analyzed over a 20-year 

timeframe. The primary cost in the 2011 analysis is the installation of 

wetline purging systems over a 20-year period, which included all new 

tank trucks during that time and, in the case of the three shorter 

compliance scenarios, the additional cost of retrofitting some tank trucks 

that would not have been replaced by the time compliance was required. 

Benefits in the 2011 analysis were the value of associated fatalities and 

other damages from wetline incidents the rule is assumed to avoid over 

the 20-year period. In the 2011 analysis, benefits are greater in the 

shorter compliance scenarios because tank trucks are equipped with 

purging systems sooner and therefore more incidents are avoided. In the 

20-year scenario, only 5 percent of trucks are equipped each year so it 

takes until year 20 when all vehicles would be equipped and all incidents 

in that year would be avoided.1

 1

In the 20-year compliance scenario, since it assumed tank trucks have a useful life of 20 

years, only new tank trucks are equipped with the wetline purging system, resulting in an 

equal number of new trucks being equipped with the system and all trucks equipped by 

the end of the 20 years.

In contrast, in the 5-year compliance 

scenario, by year 5, all future incidents are assumed to be avoided, 

resulting in greater estimated benefit, but also increased cost, due to the 

Appendix II: PHMSA’s Wetline Proposed-Rule 

Cost-Benefit Methodology and Related 

Changes
Appendix II: PHMSA’s Wetline Proposed-Rule 

Cost-Benefit Methodology and Related 

Changes

Page 49 GAO-13-721 Cargo Tank Trucks

need to equip sooner—requiring many trucks to be retrofit with purging 

systems—and the continued cost of equipping trucks in years 6-20 as 

retrofitted trucks need replacement.

In contrast, the 2012 cost-benefit analysis did not calculate all costs and 

benefits of the rule over a 20-year period, but rather calculated costs for 

each truck required to be equipped with a purging system within the 

compliance time frame and the benefits associated with that equipage for 

the remaining life of each equipped truck. This changes the number of 

years over which costs and benefits are calculated:

• For the 20-year compliance scenario, the 2012 analysis includes 

costs for equipping all new tank trucks purchased during the 20 years, 

and measures benefits for 20 years after each truck is equipped. That 

is, a truck that is bought new in year 15 will have benefits associated 

with that equipage until year 35.

• For the 5-year compliance scenario, all trucks are either equipped 

new or retrofit during the first 5 years, and the benefits associated with 

the remaining life of that truck are assessed. While trucks purchased 

new in those 5 years will have benefits measured over the 20-year life 

of each truck, the benefits associated with the retrofit trucks are 

calculated for a shorter period of time depending on PHMSA’s 

assumptions about the remaining life of those vehicles. Benefits 

accrue until a retrofitted truck is presumed retired from service.

PHMSA did not include in its 2012 assessment the costs or benefits 

associated with a new truck that would replace the truck that had been 

retrofit. For example, if a truck was retrofit in year 3 of the analysis and it 

was assumed that it had a remaining life of 10 years, benefits associated 

with that truck were included in the analysis only through year 13; the 

costs from equipping a new replacement truck in year 13 and the 

resulting benefits thereafter were not included. Consequently, the 2012 

analysis may not be comparable with the 2011 analysis, which used the 

same 20-year time-frame for the four scenarios.2

 2

In cost-benefit analyses, projects (or in this case, different compliance-date scenarios) 

should always be compared over the same discounting period since projects with different 

time frames are not directly comparable. Anthony E. Boardman et al., Cost-Benefit 

Analysis, 2nd Ed. (Upper Saddle River, N.J.: Prentice Hall, 2001), p. 133.

Further, this 

methodology does not show that equipping trucks sooner would result in 

greater societal benefit, likely because benefits are not included for new 
Appendix II: PHMSA’s Wetline Proposed-Rule 

Cost-Benefit Methodology and Related 

Changes

Page 50 GAO-13-721 Cargo Tank Trucks

trucks that would replace retrofit trucks retired within the 20 year 

timeframe. Rather, it shows the value of benefits as greater under the 

longer compliance timeframe. In contrast, the 2011 analysis shows 

greater benefit for the 5-year compliance scenario than the 20-year 

scenario, but at significantly higher cost. Table 5 compares the cost and 

benefit values and calculation methods for the 20-year and 5-year 

compliance scenarios in PHMSA’s 2011 and 2012 analyses.

Table 5: Cost and Benefit Values and Calculation Methodologies from PHMSA’s 2011 and 2012 Wetline Proposed-Rule CostBenefit Analyses

2011 analysis 2012 analysis

20-year compliance 

scenario

5-year compliance 

scenario

20-year compliance 

scenario

5-year compliance 

scenario

Costsa $52.5 million.

Cost based on equipping 

only new trucks, resulting in 

27,000 equipages that occur 

over 20 years.

$100.6 million.

Cost based on equipping 

new trucks, resulting in 

27,000 new equipages that 

occur over 20 years, and 

retrofitting existing trucks in 

use by the end of the first 5 

years, resulting in 20,500 

retrofits over the first 5 years.

$65.4 million.

Cost is based on equipping 

only new trucks, resulting in 

27,000 equipages that occur 

over 20 years.

$74.6 million.

Cost is based on equipping 

new trucks during the first 5 

years and retrofitting all other 

trucks during that period, 

resulting in 27,000 

equipages over 5 years.

Benefitsa $51.6 million.

Benefits are the value of 

wetline incidents avoided 

during the 20-year period. 

Thus, with an equal number 

of new trucks equipped each 

year, more incidents are 

avoided in later years than in 

early years.

$94.7 million.

Benefits are the value of 

wetline incidents avoided 

during the 20-year period. 

Thus, all wetline incidents 

are avoided after the first 5 

years, since all trucks are 

equipped by the fifth year, 

and a percentage of 

incidents are avoided each of 

the first 5 years based on 

how many trucks would be 

equipped that year.

$67.3 million.

Benefits are calculated for 

the useful life of each 

equipage: thus benefits are 

calculated for 20 years for 

every truck, since all 

equipages are on new trucks 

expected to last 20 years.

$54.1 million.

Benefits are calculated for 

the useful life of each 

equipage: thus benefits are 

calculated for 20 years for 

every new truck, and for 

fewer years for each 

retrofitted truck.

Source: GAO analysis of PHMSA cost-benefit analyses

a

Values are present value 2009 dollars PHMSA discounted using a 3 percent discount rate. PHMSA 

also calculated costs and benefits using a 7 percent discount rate.
Appendix III: GAO Contact and Staff 

Acknowledgments

Page 51 GAO-13-721 Cargo Tank Trucks

Susan A. Fleming, 202-512-2834, flemings@gao.gov

In addition to the individual named above, Sara Vermillion, Assistant 

Director; Amy Abramowitz; Melissa Bodeau; Geoff Hamilton; Andrew 

Huddleston; Tara Jayant; SaraAnn Moessbauer; Jaclyn Nelson; Josh 

Ormond; Madhav Panwar; Lisa Shibata; and Anne Stevens made key 

contributions to this report.

Appendix III: GAO Contact and Staff 

Acknowledgments

GAO Contact

Staff 

Acknowledgments

(541100)
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