GAO

United States General Accounting Office

Report to Congressional Committees

February 2001 HIGHWAY 

INFRASTRUCTURE

FHWA’s Model for 

Estimating Highway 

Needs Has Been 

Modified for 

State-Level Planning

GAO-01-299

Page 1 GAO-01-299 Highway Infrastructure

Contents

Letter 3

Appendixes Appendix I: Scope and Methodology 22

Appendix II: Information About HERS Models 24

Appendix III: Questionnaire for States That Asked to Participate

in FHWA’s Pilot Program for the State HERS Model 33

Appendix IV: GAO Contacts and Staff Acknowledgments 37

Tables Table 1: HERS Pilot Project States and Eight States Randomly

Selected for Interviews 23

Table 2: Key Differences Between the HERS Model and State-Level 

HERS Models 31

Figures Figure 1: Simplified Representation of the HERS Modeling Process 7

Figure 2: States Participating in the HERS-ST Pilot Program 15

Abbreviations

DOT Department of Transportation 

FHWA Federal Highway Administration

HERS Highway Economic Requirements System

HERS-ST state-level version of the Highway Economic Requirements 

System

GAO U.S. General Accounting Office

TEA-21 Transportation Equity Act for the 21st Century

GIS geographic information system

HPMS Highway Performance Monitoring System

MPO metropolitan planning organization

EPA Environmental Protection Agency

HERS/OR Oregon’s version of the Highway Economic Requirements 

System

HERS/IN Indiana’s version of the Highway Economic Requirements 

System
Page 2 GAO-01-299 Highway Infrastructure
Page 3 GAO-01-299 Highway Infrastructure

United States General Accounting Office

Washington, D.C. 20548 Letr

February 14, 2001

The Honorable Bob Smith

Chairman

The Honorable Harry Reid

Ranking Member

Committee on Environment 

 and Public Works

United States Senate

The Honorable Don Young

Chairman

The Honorable James L. Oberstar

Ranking Democratic Member

Committee on Transportation 

 and Infrastructure

House of Representatives

Federal and state governments have played a vital role in the nation’s 

economy by facilitating the movement of people and goods through 

significant investments in highways. At the federal level, the Department of 

Transportation’s (DOT) Federal Highway Administration (FHWA) uses a 

computer model known as the Highway Economic Requirements System 

(HERS) to estimate the future investment required to maintain and improve 

the nation’s highways. DOT reports the results of this analysis to the 

Congress on a biennial basis. However, state governments make a large 

number of highway infrastructure investment decisions. States currently 

use a variety of analytic tools to make these decisions. Interest in using 

HERS at the state level has grown. Two states—Indiana and Oregon—are 

already using customized versions of the model, and in December 2000, 

FHWA began a pilot project to test its state-level version of HERS, called 

HERS-ST, with interested states. 
Page 4 GAO-01-299 Highway Infrastructure

The Transportation Equity Act for the 21st Century (TEA-21) directed GAO 

to evaluate and report to the Congress on the extent to which the HERS 

model can be used to provide states with useful information for their 

planning efforts. Accordingly, this report describes (1) why FHWA 

developed a state-level HERS model, (2) how FHWA is making the statelevel HERS model available to states, (3) how states expect to use the 

model, and (4) how FHWA could improve the model, including 

improvements already planned and additional changes that might increase 

the state-level HERS model’s usefulness, including the incorporation of 

additional data. To address these issues, we built on our June 2000 report, 

which focused on the federal HERS model,1

 by reviewing documentation 

for the federal and state-level models and interviewing the models’ 

developers and managers. We interviewed FHWA officials about the HERSST pilot project. In addition, to identify how states might use the HERS-ST 

model, we first randomly selected 8 states from a list of 16 states that 

initially volunteered to participate in FHWA’s pilot project. For each of the 

selected states, we asked state transportation officials to identify how they 

plan to use the HERS-ST model and how, based on their current 

understanding, the model might be improved. Finally, to draw on the 

experiences that Indiana and Oregon have had with other state-level HERS 

models, we interviewed transportation officials from these states about 

changes that could be made to the HERS-ST model’s assumptions and data 

to improve the usefulness of the model. See appendix I for further 

information on our scope and methodology.

Results in Brief FHWA developed the HERS-ST model as an investment-analysis tool for 

highway planning at the state level. FHWA officials believe that some state 

departments of transportation will find the analysis that the HERS-ST 

model produces useful because it demonstrates the potential results of 

highway investment decisions from an economic point of view. These 

officials recognized that the national-level HERS model’s ability to compare 

the benefits of alternative highway improvements to the related costs was 

an improvement over previous highway planning models, which used 

engineering standards to identify deficiencies and select improvements 

without regard to their economic merit. They concluded that developing a 

state-level HERS model might offer states a similarly useful analytical tool. 

In addition, two states—Indiana and Oregon—recently started using their 

1

Highway Infrastructure: FHWA’s Model for Estimating Highway Needs Is Generally 

Reasonable, Despite Limitations (GAO/RCED-00-133, June 5, 2000).
Page 5 GAO-01-299 Highway Infrastructure

own customized versions of the national model. These states have already 

found their models useful for determining future highway needs and 

planning highway projects. After its positive experience with the nationallevel HERS model and the model’s successful adaptation in two states, 

FHWA began to develop HERS-ST in 1999. FHWA expects that states will 

use the HERS-ST model to facilitate planning for highway investment. 

FHWA is conducting a pilot project for its prototype HERS-ST model with 

those states that volunteered to test the model. Interest in the HERS-ST 

model has been higher than FHWA officials first expected, with 20 states 

volunteering to participate in the pilot project. In December 2000, FHWA 

distributed to these states HERS-ST software, technical manuals, and sets 

of state highway data with which to run the model. FHWA then provided an 

overall orientation and technical training and addressed states’ questions 

during a February 2001 workshop. Following a test period, FHWA plans to 

evaluate states’ interest and success in using the model and report the 

results in August 2001. On the basis of that evaluation, FHWA will make 

decisions about whether or how to expand its support for the model and 

how to improve it. 

Officials from a sample of eight of the states planning to participate in the 

HERS-ST pilot project reported that they are primarily interested in taking 

advantage of the model’s use of benefit-cost analysis to assess alternative 

highway improvements. Though these officials had not yet used the model 

nor determined all the uses to which they might put the model, they 

identified as their most likely uses (1) comparing the benefits and costs of 

making alternative highway improvements, (2) developing or refining state 

transportation investment plans, and (3) assessing highway needs forecast 

by state district offices or local agencies. They further mentioned the 

possibility of using the model to produce planning and management tools 

such as long-range state highway plans. 

If the HERS-ST pilot project shows that states view the HERS-ST model as 

a useful tool, FHWA expects to upgrade the model for future users. In doing 

so, it would consider both enhancements that have already been planned 

for the national-level HERS model and changes targeted specifically to 

HERS-ST. Enhancements planned for the national-level HERS model that 

could be incorporated into HERS-ST include an improved approach for 

calculating the long-term benefits of improvements, an improved method 

of pavement analysis, and upgrades to the model’s vehicle emissions data. 

Changes specifically to improve the HERS-ST model’s usefulness to states 

might include converting the model to a menu-driven system to improve its 
Page 6 GAO-01-299 Highway Infrastructure

ease of use or revising the model’s data input format so that it matches 

FHWA’s current state highway data reporting requirements. Our interviews 

with state officials also indicated that states might want to analyze more 

detailed highway information than HERS-ST now considers.

Background DOT submits biennial reports, called Conditions and Performance 

Reports,

2

 to the Congress, detailing the state of the nation’s highways, 

bridges, and other surface transportation systems along with investment 

requirements for these systems. In developing its portion of the report, 

FHWA bases its estimates of investment requirements for most highways 

on the Highway Economic Requirements System (HERS) computer model. 

Before using the HERS model, FHWA used an engineering model that 

compared highway conditions with engineering standards, identified 

deficiencies, and calculated investment needs by totaling the costs of fixing 

all the deficiencies. In contrast, the HERS model compares the relative 

costs and benefits associated with potential highway improvements, such 

as widening or resurfacing, to identify those that are economically justified. 

The HERS model begins by assessing the current condition of the highway 

sections in its database. It then projects the future condition and 

performance of the highway sections on the basis of expected changes in 

factors such as traffic, pavement condition, and average vehicle speed. 

(See fig. 1.) The model identifies deficient highway sections, ranks 

improvements by economic merit (benefits exceeding costs), and then 

selects improvements. Benefits considered include reductions in factors 

like travel time, vehicle operating costs, accidents, and vehicle emissions 

over the lifetime of the improvement, while costs considered include the 

capital expenditures required to construct the improvement.3

2

The most recent report in the series was 1999 Status of the Nation’s Highways, Bridges, and 

Transit: Conditions & Performance, DOT (FHWA-PL-00-016, May 2000).

3

The technical specifications for both models are documented in Highway Economics 

Requirements System Technical Report DOT (FHWA, June 2000).
Page 7 GAO-01-299 Highway Infrastructure

Figure 1: Simplified Representation of the HERS Modeling Process 

Source: FHWA data.

The total cost of constructing selected improvements represents the future 

investment requirement for highways included in the HERS model. FHWA 

can calculate these costs on the basis of several different scenarios. For 

example, under the “economic efficiency” scenario, the model selects and 

implements all the improvements for which benefits exceed costs. Under 

the “maintain current (pavement) conditions” scenario, the HERS model 

selects and implements the least costly mix of improvements that would 

maintain average pavement conditions. Under a third scenario, designed to 

address road congestion, the HERS model selects the least costly 

improvements that would maintain current travel times. 

To run the HERS model, FHWA uses highway condition and performance 

data that each state collects and annually updates on a sample of highway 

sections4

 representing different highway classes.5 The highway sections 

range in length from 1 block to 10 miles. States are to report detailed 

highway data for sampled6

 highway sections. The data include information 

on highway capacity, traffic volume, pavement roughness, lane widths, and 

Identify

deficient

sections

Assemble 

highway data 

(traffic 

forecasts,

highway 

conditions, etc.)

Forecast 

future 

condition and 

performance 

of highway 

sections

Identify 

economically 

justified 

improvements 

for deficient 

sections

Select 

section 

improvements

that satisfy 

investment 

criteria 

Combine

section

improvement

costs to

develop needs 

estimates

4

The HERS model is also capable of analyzing all sections in the highway classes it models. 

When the model uses a sample of highway sections, it also uses “expansion factors” that 

extrapolate highway conditions and improvement costs to a state or national level. 

5

FHWA maintains the resulting database, known as the Highway Performance Monitoring 

System (HPMS). The nine classes of highways reported for FHWA’s HPMS database are (1) 

urban interstates, (2) rural interstates, (3) urban freeways and expressways, (4) urban other 

principal arterials, (5) rural other principal arterials, (6) urban minor arterials, (7) rural 

minor arterials, (8) urban collectors, and (9) rural major collectors. The three FHWA 

highway classes not reported for FHWA’s HPMS database are (1) urban local roads, (2) rural 

local roads, and (3) rural minor collectors.

6

In 1997, states reported detailed data for 125,000 sampled highway sections. The number of 

sample sections was reduced to 112,000 in 1999.
Page 8 GAO-01-299 Highway Infrastructure

other physical characteristics. In addition to collecting these data, the 

states develop forecasts of traffic growth for each section.

We reviewed the HERS model and reported in June 2000 that HERS 

provided the Congress with a more useful and realistic estimate of needed 

highway improvements than earlier models had. In particular, we found 

that a major strength of the model is its ability to assess the relative 

benefits and costs associated with making alternative highway 

improvements. In addition, an expert panel of economists and engineers 

from the public and private sectors convened by FHWA in June 1999 found 

that FHWA has strengthened HERS over time and that recent refinements 

have increased the model’s applicability and credibility. Nonetheless, we 

found that the HERS model also has some limitations. First, since the 

model analyzes each highway section independently rather than the entire 

transportation system as a whole, it cannot reflect how changes in one part 

of the system might affect another part of the system, such as how traffic 

might be redistributed7

 as improvements are made. Second, the HERS 

model uses a computational “shortcut” to approximate the lifetime benefits 

associated with an improvement. Several transportation modeling experts 

have questioned whether this approach reasonably approximates future 

benefits. Third, because the HERS model is not designed to quantify the 

uncertainties associated with its methods, assumptions, and data, the 

model cannot estimate the full range of uncertainty8

 within which its 

estimates vary. Finally, the model excludes certain classes of the nation’s 

highways from its analysis, meaning that FHWA must use alternate 

methods to forecast investment needs for these classes of highways.9

7

Although the effect of this limitation is unclear, explicitly modeling the entire 

transportation network is not possible with the current state of the art in modeling or 

available data. The HERS model incorporates the concept of price elasticity, which FHWA 

officials believe captures the net effect of all changes in the transportation network. The 

model uses price elasticity to assess the response of drivers to changes in the cost of 

traveling on a highway, partly mitigating the benefits of a highway improvement. For 

example, because improving a highway lowers travel costs, some drivers may respond by 

driving more often. As a result, traffic on the improved highway may increase more quickly 

than anticipated, reducing the future benefits of the improvement. 

8

In its 1999 biennial report on investment requirements, FHWA accounted for some 

uncertainties by doing “sensitivity analyses” to measure how much its HERS estimates 

change when the value of certain key inputs or assumptions used in the model are changed.

9

The HERS model does not analyze the three classes of roads that are not included in 

FHWA’s database: rural minor collectors, rural local roads, and urban local roads. 

Furthermore, HERS does not estimate investment requirements for possible new roads.
Page 9 GAO-01-299 Highway Infrastructure

Like FHWA, state departments of transportation undertake planning and 

reporting activities to manage their highways and determine their capital 

needs. For example, under federal transportation planning requirements, 

states must carry out a process for considering the effect of transportation 

projects on a variety of factors, including the economy and the 

environment. States are also required to develop both long-range plans 

covering at least 20 years and transportation improvement programs (state 

investment plans) that cover at least 3 years. These requirements help 

ensure that state transportation projects come from a systematic planning 

process rather than from a “wish list” of transportation projects. To meet 

these planning and reporting requirements, some state DOTs have had to 

rely on their technical capabilities. Many states have developed pavement 

management systems to help them systematically analyze data on existing 

highways and project future pavement needs. For example, several states 

have used models, based on pavement engineering criteria, to analyze 

pavement needs either at the project level or for a whole statewide 

network. Some states have also adopted a predecessor of the HERS model 

developed by FHWA, called the Analytic Process model, that compares 

highway conditions with engineering criteria to identify potential 

improvements.

After FHWA developed the HERS model, two states contracted to have 

customized state-level HERS models developed for them. Oregon DOT, 

when updating its long-range statewide highway plan, hired the same 

consultant that had produced HERS for FHWA. That consultant 

recommended that Oregon DOT use a customized version of the HERS 

model for its statewide plan. Similarly, when Indiana DOT engaged the 

same consultant for a corridor planning study,10 the consultant 

recommended that Indiana DOT use a customized version of the HERS 

model for its corridor planning analysis. Indiana DOT subsequently used its 

model’s results to draft a new statewide highway plan.

10Corridor planning studies examine the feasibility of future highway improvements. A 

corridor connects significant end points and typically is longer than any single highway 

project. Corridor studies are initiated well in advance of specific improvement projects, 

allowing a highway agency to secure or preserve rights-of-way before any actual projects 

are initiated.
Page 10 GAO-01-299 Highway Infrastructure

FHWA Developed the 

HERS-ST Model as an 

Investment Analysis 

Tool for Highway 

Planning at the State 

Level

After its positive experience with the national-level HERS model and the 

model’s successful adaptation in Oregon and Indiana, FHWA began to 

formally develop HERS-ST in 1999. FHWA expects that states will use the 

model in a variety of ways to facilitate planning for highway investment. 

The National-Level HERS 

Model Produces Useful 

Information About Highway 

Investments

Our review of the national-level HERS model showed that its results 

provide legislative and executive branch officials with useful information 

for decisions about highway investments. Legislative branch officials said 

they use the estimates to obtain general information on the nation’s need 

for infrastructure investments and find the HERS estimates more useful 

than previous estimates that were based on engineering analyses alone. 

FHWA views the national-level HERS model as a step forward in its efforts 

to meet the statutory requirement to report on the conditions and 

performance of the nation’s highways and future national highway 

investment requirements. FHWA officials also said that the HERS model’s 

benefit-cost approach complies with an executive order11 that requires 

federal spending for infrastructure to be based on a systematic analysis of 

expected benefits and costs. FHWA concluded that state transportation 

and other officials might find HERS-type analysis helpful in analyzing 

highway investments as well as supporting federal planning requirements.

Two States Are Using 

Customized Versions of the 

HERS Model 

Facing increased funding constraints along with a greater demand for 

expenditure accountability, Oregon officials made use of a customized 

HERS model to prioritize needs and determine deficiencies in its highway 

system.12 Oregon officials cite their HERS model’s effective use of benefitcost analysis as a foundation for determining the best combination of 

11Executive Order 12893, Principles for Federal Infrastructure Investments (1994), discusses 

the importance of continuous infrastructure investment to sustained economic growth. The 

order directs federal agencies with infrastructure investment responsibilities to plan for 

investments using a systematic analysis of expected benefits and costs.

12Oregon received its customized version of the HERS model in early 1998. 
Page 11 GAO-01-299 Highway Infrastructure

improvements and for allocating resources between programs. Oregon 

officials have found these benefit-cost results useful for highway planning, 

corridor planning, and goal setting. For example, when analyzing the 1999 

Oregon Highway Plan (an element of the required long-range plan), state 

officials evaluated investment tradeoffs between system preservation 

projects—capital projects that ensure that a highway continues to serve its 

intended purpose—and modernization projects—capital projects that 

typically increase capacity. Oregon’s report said that this analysis helped 

the Oregon Transportation Commission gain a clear picture of the 

condition of the highway system under different funding scenarios and thus 

helped the Commission make difficult investment decisions. (See app. II 

for information on the technical features of the Oregon model.)

Indiana’s DOT sought out a modified version of the HERS model in an 

attempt to improve its planning process and, more specifically, to 

strengthen its technical planning tools.13 Indiana officials wanted a model 

that would analyze benefits and costs for all of the state’s highway projects, 

and they decided that a modified version of the HERS model would meet 

their needs. These officials used their HERS model to analyze highway 

investment needs over a 25-year period, including a comparison of the 

status of the highway system at different levels of funding. In addition, 

Indiana officials used their model to analyze highway investment needs at 

the district level within the state. The Indiana model has a unique feature 

that links specific model results with a geographic information system 

(GIS) that visually displays results on state highway maps. This feature 

allows the staff to compare district offices’ and metropolitan planning 

organizations’ priorities with the ones the model identifies. (See app. II for 

information on the technical features of the Indiana model.)

13Indiana received its customized version of the HERS model in 1998.
Page 12 GAO-01-299 Highway Infrastructure

FHWA Developed the 

HERS-ST Model to Help 

States Plan and Manage 

Their Highways 

After FHWA officials reviewed their positive experience with HERS, along 

with the positive experiences of Oregon and Indiana with their customized 

HERS models, they decided to consider developing a HERS model that all 

states could use. FHWA’s Office of Asset Management14 commissioned two 

studies to identify the potential role of a HERS model in helping states 

assess their highway investment needs and develop state highway plans. 

The studies demonstrated a potential state interest in a state-level HERS 

model. Therefore, FHWA developed a prototype state model, HERS-ST, 

from the national-level HERS model that any state could use for planning 

and programming activities. FHWA officials believe that states could use 

the HERS-ST model to perform benefit-cost analysis on highway 

improvements and to forecast the future condition and performance of 

state highway systems. In addition, the Office of Asset Management’s Asset 

Management Primer15 explains that HERS-ST has the potential to help 

state-level policy makers address resource allocation questions because 

the model can analyze “what if” questions using specific funding levels. For 

example, the model can show the long-term effects that different levels of 

spending or different emphases in investment could have on the condition 

and performance of highways. The primer also states that the model may 

even help some states meet new Government Accounting Standards Board 

provisions requiring states to report the cost of maintaining their 

transportation infrastructure assets.16

The HERS-ST model that FHWA developed is based on and operates in 

much the same way as the national-level HERS model, with a few 

noteworthy differences. Like the HERS model, HERS-ST (1) projects the 

future condition and performance of a state’s highway system, (2) assesses 

whether any highway improvements are warranted, and (3) selects 

14FHWA established the Office of Asset Management in February 1999 to help states 

systematically manage and analyze their highway assets. FHWA is to encourage states to 

systematically analyze the benefits and costs of highway infrastructure investments, 

according to Executive Order 12893.

15Asset Management Primer, DOT (FHWA-IF-00-010, Dec. 1999).

16Starting in 2001, state governments will have to follow a new accounting standard, known 

as GASB Statement No. 34, that generally requires governments to report their 

infrastructure assets at historic cost and depreciate them over time. Since depreciation may 

not always be appropriate, the rule also allows governments with adequate asset 

management systems to disclose the estimated amount required each year to maintain and 

preserve their assets. The HERS-ST model may help governments follow this second 

approach.
Page 13 GAO-01-299 Highway Infrastructure

appropriate improvements using benefit-cost analysis. One difference 

between the HERS and HERS-ST models is that the HERS-ST model has an 

“override” feature that allows a state official to override highway 

improvement selections made by the model in order to reflect specific, 

local conditions. According to FHWA officials, the model’s override feature 

will enable state officials to apply specific knowledge about highway 

improvements (such as whether implementing a particular improvement is 

feasible) that may not be reflected in the model’s database. For example, an 

official might specify that the model reconstruct a highway section rather 

than resurface it because of problems with the underlying structure of the 

pavement that are not yet apparent from measurements of the pavement’s 

roughness. The override feature is unique to the HERS-ST model. Another 

difference is that the HERS-ST model is capable of providing detailed 

results about each of the highway sections it analyzes, including 

information on the particular improvement selected, the expected future 

condition of the section, and the benefits and costs of making the 

improvement. By contrast, the HERS model generates only summary 

results for the classes of roads it analyzes.

In addition to these differences between the two models, the HERS-ST 

model offers states further options regarding what data to consider. State 

officials can adjust the HERS-ST model to reflect state conditions by, for 

example, using state highway construction costs rather than national 

average costs. And state officials may use HERS-ST either to analyze the 

statistical sample of their state’s highways included in FHWA’s Highway 

Performance Monitoring System (HPMS) database or, if they have the 

appropriate data, to analyze all highway sections in the state’s system. 

While the HERS model could also analyze all highway sections, it is 

currently limited to analyzing only the sample of sections in the HPMS 

database. When the HERS-ST model’s projections are based on sampled 

sections in the HPMS database, the projections may not account for all the 

highways for which a state department of transportation is responsible.17

However, the state can, if it has appropriate data on all its highway 

sections, use the HERS-ST model to analyze every section in the state 

highway system, as Oregon and Indiana did with their customized HERS 

17The sample data may exclude highways for which the state is responsible, like local roads 

or rural minor collectors, or include highways for which the state is not responsible. For 

example, according to an Indiana official, Indiana’s sample data addresses 30,000 miles of 

highway, of which only 12,000 miles are within state jurisdiction.
Page 14 GAO-01-299 Highway Infrastructure

models. (See app. II for a more detailed comparison of the national-level 

HERS and HERS-ST models.)

FHWA Provided HERSST to States Through a 

Pilot Project

FHWA distributed the prototype HERS-ST model software to 20 states 

volunteering to participate in its pilot project, which is intended to gauge 

interest in the model and to further identify potential uses for and revisions 

to it. Interest in the model was higher than FHWA expected. According to 

an FHWA official, the agency expected to have five states participate in the 

pilot. However, the number of interested states grew to 20, including 

Indiana and Oregon, before the pilot began. (See fig. 2.) Indiana and Oregon 

officials said they wanted to participate in the pilot program to learn about 

new features incorporated into the HERS-ST model and to share their 

customized HERS model experience with other pilot states.
Page 15 GAO-01-299 Highway Infrastructure

Figure 2: States Participating in the HERS-ST Pilot Program

Source: FHWA information.

In December 2000, FHWA distributed the model, along with technical 

manuals and state-specific sample data on highway sections needed to run 

the model, to the 20 pilot project states. This distribution took place about 

2 months before the pilot’s February 2001 kickoff workshop in New 

Orleans, Louisiana. The workshop was designed to train participating 

states in the use of the HERS-ST model. It included general information on 

the use of the model, information on Indiana’s and Oregon’s experiences 

with their customized HERS models, and technical review and training. 

FHWA officials plan to focus their efforts during the pilot program on 

providing technical support to participating states. FHWA officials also 

Pilot states (as of Dec. 11, 2000)
Page 16 GAO-01-299 Highway Infrastructure

hope to provide training for state policymakers to explain how the HERSST results can be used.

FHWA anticipated that the pilot project would conclude after 

approximately 2 months. However, the agency was prepared to extend the 

duration of the pilot if states indicated that additional time would be 

helpful. At the conclusion of the pilot, participants will be asked to report 

on (1) their experiences testing the model, (2) their assessment of the 

model’s usefulness in state planning and programming activities, and (3) 

their recommendations for further FHWA initiatives with respect to the 

model. FHWA expects to report by August 2001 on states’ comments and its 

own recommendations for further HERS-ST model initiatives. FHWA 

officials said that the agency will consider changes to the HERS-ST model 

at the end of the pilot project, depending on the number of states that 

identify particular changes as important. 

States Participating in 

FHWA’s Pilot Project 

Expect to Use HERSST to Supplement 

Their Planning Tools 

With Economic 

Information 

Officials from almost all of the eight states we randomly selected18

indicated that although they had limited knowledge about HERS-ST, they 

were looking forward to expanding their states’ technical tools to better 

support their planning processes. When asked why they planned to 

participate, the state officials said that, while they did not have details of 

how the model works, they did not want to miss out on any tool that might 

improve their planning and highway management. In general, the state 

officials also expressed some level of dissatisfaction with their current 

planning tools. As one state official explained, her DOT was always looking 

to improve its planning process. (See app. III for the results of our 

discussions with state officials about the HERS-ST model.)

A number of state officials indicated that the HERS-ST model’s benefit-cost 

analysis capability is an important feature that made the model attractive to 

them. In response to a question about why states wanted to participate in 

the pilot, officials from most of the states said that they hoped the model 

would help improve their knowledge about the economic impact of 

investment decisions. Officials from five of these states believe this would 

help the states prioritize projects and maximize the effect of their spending. 

An official in one state said that the state’s highway funding depends, in 

18See app. I for details of our methodology for selecting eight states to interview from among 

the states considered likely to participate in the HERS-ST pilot program when we contacted 

FHWA in September 2000.
Page 17 GAO-01-299 Highway Infrastructure

part, on a study of infrastructure needs. However, the state’s infrastructure 

study is based on the assumption that highway funding is unlimited. Thus, 

the official believes the results of the needs study are unrealistic. The 

official hopes HERS-ST can contribute economic reality to the state 

highway funding plan.

When presented with a list of potential uses for the HERS-ST model results, 

state officials we interviewed said that, if the model provided realistic 

results, they would consider using the results in the following tasks:

• comparing benefits and costs of making alternative highway 

improvements;

• developing state highway plans, such as state transportation investment 

plans, long-range highway plans, local highway needs forecast 

assessments, and corridor studies;

• satisfying the requirements of the Government Accounting Standards 

Board’s provisions for reporting on the value of transportation 

infrastructure assets;

• allocating funds to offices within the state highway agency (for example, 

by district). (See app. III for a more detailed list of potential uses.)

For example, one state official indicated that his state plans to update its 

long-range highway plan shortly and hopes that HERS-ST may be useful for 

that work. Overall, officials indicated that the three most important uses 

for their states would probably be (1) performing benefit-cost analysis of 

alternative highway improvements, (2) developing or refining state 

transportation investment plans, and (3) assessing highway needs forecast 

by state district offices or local agencies.

Potential 

Improvements to the 

HERS-ST Model 

If states involved in the pilot project find that the HERS-ST model is useful, 

FHWA expects to upgrade it for future state users. First, FHWA plans to 

make certain changes to the HERS-ST model to keep it current with 

analytical improvements planned for the national-level HERS model. 

Second, FHWA is considering changes designed to make the model easier 

for states to use. Finally, states might also ask that FHWA enhance the 

HERS-ST model so it can analyze more detailed highway information.

FHWA Plans to Upgrade 

HERS-ST

According to FHWA officials, if the pilot participants find the HERS 

concept attractive, FHWA will, as appropriate, provide for revising the 

HERS-ST model so that it will benefit from upgrades to the national-level 
Page 18 GAO-01-299 Highway Infrastructure

version of the model. FHWA officials said their improvement plans for the 

national-level version of HERS include eliminating the computational 

shortcut that we identified as a limitation in our June 2000 report. This 

shortcut is designed to approximate the lifetime benefits associated with a 

highway improvement. However, the approximation may not fully 

represent the lifetime benefits, and FHWA officials acknowledge that 

improvements in computing power have made it unnecessary. FHWA also 

plans to change the national-level HERS model by

• incorporating pavement performance data based on climate zones 

instead of assuming one rate of pavement deterioration,

• revising its highway-capacity analysis to reflect changes in the 

Transportation Research Board’s Highway Capacity Manual,

• revising the emissions data used as soon as the Environmental 

Protection Agency finishes revising its emissions model, and

• updating pavement improvement costs, currently based on 1988 data, to 

represent 1998 or 1999 data.

HERS-ST Could Be Modified 

to Make the Model Easier 

for States to Use

As part of its evaluation of the pilot project, FHWA plans to ask state 

officials for suggestions of potential improvements to the model. Assuming 

the project continues past the pilot phase, FHWA officials say they will 

consider making those changes that will benefit multiple states. Our 

interviews with state, FHWA, and other officials indicate that states may 

ask FHWA to modify HERS-ST in ways that make the model easier to use 

without altering the model’s analytical structure. One state official 

expressed concern over the user-friendliness of the model, having heard 

that the HERS-ST program is not user-friendly because it operates in an 

older DOS-based computer environment that department staff might not be 

familiar with. An FHWA consultant reviewing the HERS model concluded 

that updating the model so that it can operate in a more user-friendly menudriven environment might be the key to increasing the number of states 

that use the model. FHWA officials agreed that a menu-driven program 

would make the model easier for states to use.

The HERS-ST model would also be easier for states to use if it accepted 

highway data in the same format that states use in their annual data 

submissions for FHWA’s HPMS database. The HERS-ST model requires 

input in the 1993 data reporting format, not the current HPMS format. To 

assist states participating in the pilot project, FHWA provided each one 

with its highway data already reformatted for use with the HERS-ST model. 

However, state officials wishing to analyze other highway sections in their 
Page 19 GAO-01-299 Highway Infrastructure

states would have to reformat their data to the older format before the 

model could use it. An FHWA consultant, commenting on ways that the 

HERS model could be more useful to states, recommended that the model 

accept data corresponding to the latest format that FHWA requires for state 

HPMS data submissions. FHWA officials recognize that widespread use of 

the HERS-ST model would require addressing this situation.

HERS-ST Could Be Modified 

to Better Fit States’ Analytic 

Needs

Our interviews with state and FHWA officials indicate that some states 

would like the HERS-ST model to analyze more detailed pavement 

management data. Many states have developed sophisticated pavement 

management systems that analyze more data than the pavement 

deterioration analysis done in the HERS or HERS-ST models. For example, 

a number of states already have pavement management systems that 

consider several types of pavement distress data. HERS-ST, like the HERS 

model, relies on data states report in the form of the International 

Roughness Index19 or the Present Serviceability Rating.20 Officials from 

four of the states we spoke with reported that they collect both roughness 

index data and serviceability rating data. However, these officials noted 

that they do not use roughness index data for planning purposes, preferring 

to rely on their serviceability rating or the other data for highway system 

planning. Officials from half of the states we contacted said they only 

collect roughness index data at FHWA’s request and they base their internal 

planning analysis on pavement rating data in their pavement management 

systems. In addition, officials from two states said they were not satisfied 

with the quality of their states’ roughness index data and preferred to rely 

on their pavement rating data.

FHWA officials also said they expect to address some of these concerns by 

incorporating more pavement distress data in the HERS model at some 

19The roughness index is based solely on surface roughness measurements. Most states 

collect these data with specially equipped vans traveling at highway speeds. FHWA instructs 

states to report the roughness index for all the major roads in the country. FHWA 

encourages states to report the index for all other highway sections sampled for the national 

highway database.

20The serviceability rating is a subjective approach for quantifying pavement condition. Prior 

to 1993, FHWA asked states to report the serviceability rating for all highway sections in its 

national highway database. FHWA still allows states to report serviceability ratings for 

highway sections in its national database that are not major roads. If a state reports both 

roughness index data and serviceability rating data to FHWA, the HERS model uses the 

roughness index data for analysis.
Page 20 GAO-01-299 Highway Infrastructure

point in the future. However, they will not do so until such data are 

available to FHWA from all the states.21 FHWA officials said they are willing 

to support only one version of the HERS-ST model. But because states use 

various pavement distress measures, it is not clear to FHWA officials 

whether including these additional pavement data in the HERS-ST model 

would satisfy all states’ concerns.

Agency Comments and 

Our Evaluation 

We provided a draft of this report to the Department of Transportation for 

review and comment. Officials from the Department generally agreed with 

the report. These officials also provided technical and clarifying comments, 

which we incorporated into the report as appropriate.

We conducted our review from June 2000 through February 2001 in 

accordance with generally accepted government auditing standards. 

We will send copies of this report to cognizant congressional committees; 

the Honorable Norman Y. Mineta, Secretary of Transportation; and the 

Administrator, Federal Highway Administration.

If you or your staff have any questions about this report, please contact me 

at (202) 512-2834. Appendix IV lists key contacts and contributors to this 

report.

Phyllis F. Scheinberg,

Director, Physical Infrastructure Issues

21Officials from the states we spoke with reported that their pavement planning data include 

pavement condition measures beyond roughness, such as rutting, cracking, and faulting. 

The American Association of State Highway and Transportation Officials recently developed 

standards for roughness, rutting, and faulting and is developing a standard for cracking.
Page 21 GAO-01-299 Highway Infrastructure
Page 22 GAO-01-299 Highway Infrastructure

Appendix I

Scope and Methodology ApApenednxidexiIs

To determine why the Department of Transportation’s (DOT) Federal 

Highway Administration (FHWA) developed a state-level version of the 

Highway Economic Requirements System (HERS) computer model and 

how FHWA expects that states will use the model, we first reviewed our 

work and resulting June 2000 report on the strengths, limitations, and uses 

of the national HERS model. We then interviewed FHWA officials about 

their state-level HERS model (HERS-ST). We also reviewed FHWA 

documents about the HERS-ST model and projects in FHWA’s Office of 

Asset Management. Finally, FHWA officials and HERS contractors told us 

that two states—Indiana and Oregon—were using state-level HERS 

models. We visited Indiana and Oregon to discuss the use of these models 

with officials in the Indiana and Oregon state departments of 

transportation and obtained and reviewed available model documentation 

and state products generated using their HERS models.

To determine how FHWA is making the state-level HERS model available to 

states, we spoke with FHWA officials about their pilot-project plans. We 

also reviewed the pilot project workshop agenda and attended the 

workshop in February 2001. We reviewed HERS-ST model documents, 

including the draft Highway Economic Requirements System Technical 

Manual and the draft Highway Economic Requirements System Users 

Manual, and we talked with model developers to determine how the model 

was developed. Finally, we reviewed FHWA’s evaluation plan for the HERSST pilot project and the time frame for the project.

To determine how states expect to use the HERS-ST model and its results, 

we reviewed reports by FHWA consultants on the potential role of HERS in 

state-level investment decisions and talked with officials from a random 

selection of 8 of the 16 states that planned to participate in FHWA’s pilot 

project. The 16 states represent all states that FHWA reported were 

planning on participating in FHWA’s pilot program as of September 5, 2000, 

with the exception of Indiana and Oregon. We excluded Indiana and 

Oregon from this random sample because both states are already using 

customized state-level HERS models, and we were already planning to 

conduct site visits for these two states. Table 1 shows the 8 states we 

contacted, as well as the 16 states from which we chose the sample.
Appendix I

Scope and Methodology

Page 23 GAO-01-299 Highway Infrastructure

Table 1: HERS Pilot Project States and Eight States Randomly Selected for 

Interviews

Note: These 16 states represent the states that were included in FHWA’s pilot project as of September 

5, 2000, with the exception of Indiana and Oregon. Randomly selected states are in bold.

Source: FHWA information.

To obtain consistent information from the eight states we contacted, we 

used a semi-structured interview format. See appendix III for a copy of the 

interview document with the results of our discussions with the eight 

states. As of December 11, 2000, the number of states that planned to 

participate in FHWA’s HERS-ST pilot had grown to 20. See figure 2 in the 

letter for a map of the 20 states.

To identify potential changes that could be made to the model, we 

discussed this issue with a wide variety of groups, including FHWA 

officials, the consultant who developed the HERS-ST and the Indiana and 

Oregon HERS models, state officials using the Indiana and Oregon models, 

state officials planning on using the HERS-ST model, and others, such as 

academics, who have used the HERS model. We also reviewed information 

on pavement measurement data, including our previous work on pavement 

measures.1

Universe of states and selected states

Arizona Missouri

Arkansas Nebraska

Delaware New Jersey

Florida New Mexico

Iowa Ohio

Louisiana Pennsylvania

Maine Rhode Island

Michigan Utah

1

Transportation Infrastructure: Better Data Needed to Rate the Nation’s Highway Conditions 

(GAO/RCED-99-264, Sept. 27, 1999).
Page 24 GAO-01-299 Highway Infrastructure

Appendix II

Information About HERS Models ApendxiI

This appendix describes technical aspects of the HERS computer model 

and the three related models designed for use by state highway planners. 

FHWA’s HERS Model The HERS model simulates infrastructure improvement decisions for the 

highways it models by comparing the relative benefits and costs associated 

with alternative improvement options. In conducting its analysis, HERS 

uses an extensive set of data that are primarily collected and updated by 

the states and maintained by FHWA in the Highway Performance 

Monitoring System database. In addition, the HERS model performs its 

analysis using several submodels representing specific highway processes, 

including traffic growth, pavement wear, vehicle speed, accidents, and 

highway improvement costs. The analysis, which is based on the current 

condition of the highway system, is conducted over four 5-year periods, for 

a total of 20 years. The HERS model draws information from the database 

and analysis from the submodels to identify deficient sections, evaluate 

alternative improvement options, and select and implement improvements. 

HERS uses benefit-cost ratios (benefits divided by costs) to evaluate and 

select improvements under several investment scenarios that FHWA 

developed. The benefits include reductions in travel times, vehicle 

operating costs, and agency maintenance, while the costs include the 

capital expenditures necessary to construct the improvement. The model 

reports its results in a series of tables showing the cost of improvements 

needed to support the model’s investment decisions for each highway class 

and funding period analyzed.

 The HERS model has several strengths:

• The model’s major strength is its ability to assess the relative benefits 

and costs associated with alternative options for making improvements 

on the nation’s highways. The HERS model selects for implementation 

only those improvements that are economically justified according to its 

analysis, a significant improvement over FHWA’s previous methods, 

which used engineering standards to identify deficiencies and select 

improvements without regard to economic merit.

• Another strength of the HERS model is that FHWA has consulted with 

experts in order to assess the model’s reasonableness and improve it. 

For example, in June 1999, FHWA convened an expert panel consisting 

of economists and engineers from the public and private sectors. This 

panel found that FHWA has strengthened the model over time and that 

the recent refinements have increased its applicability and credibility. 
Appendix II

Information About HERS Models

Page 25 GAO-01-299 Highway Infrastructure

The HERS model has some limitations:

• First, because the HERS model analyzes each highway section 

independently rather than the entire transportation network, it cannot 

completely reflect changes occurring among all highways and modes in 

the transportation network at the same time. For example, it will not 

reflect how, as improvements are made, traffic might be redistributed 

from other existing highway sections to an improved highway section. 

By incorporating price elasticity into the model, FHWA officials assume 

that the model captures the net effect of all changes in the 

transportation network as well as in the overall economy. Although the 

implication of this limitation is unclear (it may over- or under-state the 

effect of changes in traffic resulting from a highway improvement), 

explicitly modeling the entire transportation network is not possible 

with the current state of the art in modeling or available data. 

• Second, because the HERS model is not designed to quantify the 

uncertainty associated with its methods, assumptions, and data, the 

model cannot estimate the full range of uncertainty within which its 

estimates vary. As a result, the precision of the model’s estimates is 

unknown. The HERS model’s estimates rely on a variety of estimating 

techniques and hundreds of variables, all of which are subject to some 

uncertainty. However, changing the model to fully account for 

uncertainty in its factors is not likely to be cost-effective because it 

could require extensive and expensive reprogramming. We 

recommended in our June 2000 report that FHWA clarify, when 

publishing the results of HERS model analyses, that there is uncertainty 

associated with the results. State-level users can account for some 

uncertainty by conducting “sensitivity analyses” to measure how much 

the model estimates change when the values of certain key inputs or 

assumptions used in the model are changed. 
Appendix II

Information About HERS Models

Page 26 GAO-01-299 Highway Infrastructure

• Third, the HERS model uses a computational “shortcut” to approximate 

the lifetime benefits associated with an improvement. Conceptually, 

benefits such as reductions in travel time accrue over each 

improvement’s full lifetime, 20 years or more. However, in its initial 

evaluation of whether to improve a highway section, the HERS model 

calculates benefits only during the first 5-year period. To account for the 

benefits accruing after the first 5-year period, FHWA developed a 

shortcut that essentially uses an estimate of the improvement’s 

construction cost as a proxy for the improvement’s remaining future 

benefits.1

 FHWA developed the shortcut several years ago, when 

limitations in computer processing power necessitated simplifying some 

of the calculations. Given recent improvements in computing power, 

FHWA officials plan to modify the HERS model to account for lifetime 

benefits and see correcting the shortcut as a potential improvement for 

the HERS-ST model as well.

• Fourth, although FHWA has taken steps to ensure that the data used in 

the HERS model are reasonable, some of these data vary in quality. For 

example, the model uses emissions data that may not be representative 

of actual conditions. To estimate the emissions associated with traffic 

on a given section, the model uses information from the Environmental 

Protection Agency (EPA) on emissions rates per vehicle type and speed. 

Vehicle emissions, however, may depend more on how the vehicle is 

driven than on the total miles driven. FHWA officials told GAO they will 

update these data once EPA finishes revising its emissions data. In 

addition, we reported earlier that the pavement roughness data reported 

by the states to FHWA are not comparable, partly because the states use 

different devices and approaches for measuring roughness.2

 The HERS 

model uses the roughness data in projecting the pavement condition of 

each section. FHWA is supporting efforts to standardize states’ 

pavement roughness measurements. Moreover, some information used 

in the model is dated. For example, the pavement resurfacing costs used 

in the HERS model are based on 1988 data (adjusted for inflation from 

1988 to 1997). FHWA officials said they plan to update the HERS model’s 

resurfacing costs, and the HERS-ST model offers users the option of 

introducing their own construction cost data.

1

With this shortcut, the HERS-ST and HERS models assume that the remaining future 

benefits of an improvement can be approximated by the costs that would be avoided by 

making the improvement in the current 5-year period. 

2

Transportation Infrastructure: Better Data Needed to Rate the Nation’s Highway Conditions

(GAO/RCED-99-264, Sept. 27, 1999).
Appendix II

Information About HERS Models

Page 27 GAO-01-299 Highway Infrastructure

HERS Model Used in 

Oregon

The Oregon Department of Transportation obtained the first customized 

HERS model in 1998. Oregon hired a consulting firm, Cambridge 

Systematics, Inc., to help the state develop a long-range statewide highway 

plan. The consulting firm, which also developed the HERS model for 

FHWA, worked with Oregon officials to customize the HERS model, which 

resulted in the creation of HERS/OR. Oregon never received specific 

documentation for its model. But according to Oregon officials and the 

consultant, the model differs from the national-level HERS model in the 

following ways:

• HERS/OR allows the user to override the model’s improvement 

decisions for specific sections, for example, for a road that cannot 

feasibly be widened due to a nearby mountain.

• HERS/OR’s output includes two innovations: a section-by-section report 

providing details on individual improvements for each segment for each 

funding period and a revised summary table of improvements for the 

state’s four unique highway classifications.

• HERS/OR’s procedures for analyzing price elasticity are rudimentary 

when compared with the current HERS model, and data on vehicle 

accident costs are older. 

HERS Model Used in 

Indiana

The Indiana Department of Transportation contracted in 1998 for a 

customized HERS model known as HERS/IN. HERS/IN is also similar to 

HERS, but has more unique features than HERS/OR:

• HERS/IN, like HERS/OR, analyzes all sections of its state highway 

system.

• HERS/IN uses its own data on construction costs, allowing the model to 

base its estimates of construction costs on more exact, local data.

• HERS/IN is capable of using pavement improvement decisions from the 

state’s sophisticated pavement management system. However, Indiana 

DOT staff had not used this feature by the time we conducted our work.

• Unlike the national-level HERS model, HERS/IN allows its user choices 

for overriding modeled improvement decisions. For example, the user 

can specify the type of improvement, its cost, its timing, and the 

improvement’s effect on highway capacity. Indiana DOT has not used 

this feature, according to officials.

• HERS/IN’s output includes the basic national-level HERS output tables, 

plus section-by-section improvement tables like those of HERS/OR and 

tables that summarize highway improvements’ benefits for users due to 
Appendix II

Information About HERS Models

Page 28 GAO-01-299 Highway Infrastructure

decreased travel time, decreased operating costs, and increased 

highway safety. In addition, HERS/IN’s output is used to generate maps 

to display the location of its improvement plans. The model is designed 

to feed its output data into a geographic information system software 

package that produces maps of the model’s proposed improvements. 

The Indiana Department of Transportation officials said that this feature 

improves their ability to display the location of the HERS/IN model’s 

decisions to policymakers. Furthermore, the maps help the state staff 

determine whether or not HERS/IN’s decisions are realistic. For 

example, if two major improvements are proposed for nearby sections 

of highway, the maps could alert the agency that, to avoid traffic 

problems in that area, the projects should not be performed 

simultaneously.

• HERS/IN is able to consider the construction of new highways that 

might be needed to provide capacity for future travel demand. The 

Department has a sophisticated travel-demand model that supports this 

HERS/IN feature. Found in no other version of the HERS model, this 

feature allows Indiana DOT to specify new highways and the effect of 

capacity improvements on traffic systemwide, as well as to compare 

alternative improvements for addressing a capacity problem. Indiana 

DOT has not used this feature, according to officials.

• Unlike the HERS model, the HERS/IN model is not used to assess the 

effect of highway travel on the environment. According to state officials, 

the HERS/IN model could take environmental data into account when 

making its decisions, but the officials did not feel this feature was 

feasible in their model. 

The HERS-ST Model The HERS-ST model is the most recently designed HERS model. Generally, 

HERS-ST offers the analytic approaches available in the most recent HERS 

model revision. Because it is based on the HERS model, it has the same 

strengths and limitations that were noted above. However, the HERS-ST 

model differs from the national-level HERS model in the following ways:

• Unlike the HERS model, the HERS-ST model has an “override” feature 

that allows a user to override some or all of the improvement decisions 

made by the model. For example, the user can specify the particular 

type of improvement to be made on a highway section in any particular 

funding period. In the override mode, the model selects the userspecified improvements regardless of whether they are economically 

justified. According to FHWA officials, the model’s override feature will 

enable state users to apply specific knowledge about highway 
Appendix II

Information About HERS Models

Page 29 GAO-01-299 Highway Infrastructure

improvements (such as whether implementing a particular 

improvement is feasible) that may not be reflected in the model’s 

database. 

• In addition to the override feature, the HERS-ST model differs from 

HERS in the number of highway classes it can analyze and the level of 

detail of the results it generates. For example, the HERS-ST model can 

analyze highway sections from all 12 of FHWA’s classes of roads, 

including rural minor collectors and urban and rural local roads. The 

HERS model is designed to analyze sampled sections from 9 of the 12 

highway classes. Also, the HERS-ST model is capable of providing the 

user with detailed results on the highway sections it analyzes, including 

information on the particular improvement selected, the expected 

future condition of the section, and the benefits and costs of making the 

improvement. FHWA officials stated that this feature would enable the 

state user to study what happens on individual sections. By contrast, the 

HERS model generates only aggregate results for classes of roads. 

• Both the HERS-ST and the HERS models also use data from studies of 

the national economy. However, the state user can modify some of these 

data to reflect conditions in his or her state. For example, both models 

count as a benefit any reduction in travel time brought about by a 

highway improvement. In making this calculation, FHWA uses average 

national hourly compensation data from the Department of Labor’s 

Bureau of Labor Statistics to quantify the dollar value of travel time 

saved by travelers on work-related trips. In the HERS-ST model, the 

state user could substitute state-level data to derive an alternative 

estimate of travel time savings. 

The HERS-ST model also offers the state user a choice between analyzing a 

statistical sample of highways represented in FHWA’s HPMS database or 

the option of analyzing all highway sections in the state’s system.
Appendix II

Information About HERS Models

Page 30 GAO-01-299 Highway Infrastructure

State Use of the HERS 

Model 

While the HERS-ST model pilot project is FHWA’s first attempt to promote 

state use of a HERS model, the agency previously released copies of the 

HERS model. The model’s existence was well publicized because it had 

been described in DOT’s biennial Conditions and Performance reports 

starting with the 1995 edition,3

 it was profiled in studies,4 and it was cited in 

TEA-21. By 1998, FHWA was providing HERS model documentation and 

computer files to parties who requested them. FHWA reported that 18 

requesters, including state DOT officials, academics, and consultants, 

obtained copies of the model between April 1998 and September 2000. 

Michigan DOT officials who obtained copies of the model found that it did 

not suit their needs. They said that the HERS model was not useful to them 

because it would not handle all of the roads the department needed to 

study; available data would need reformatting to work with the model; and 

the results were aggregated at the network level, which was too general to 

be useful for the state’s purposes. On the other hand, a researcher at North 

Dakota State University’s Upper Great Plains Transportation Institute 

found the HERS model useful for state-level applications. He analyzed 

intermodal freight diversion (rail to truck or truck to rail) on behalf of two 

state transportation agencies. He also used HERS equations to analyze 

rural highway preservation for a third state transportation agency.

To compare key differences between the HERS model and related statelevel models, see table 2.

3

1995 Status of the Nation’s Surface Transportation System: Condition and Performance, 

Report to Congress, DOT (FHWA-PL-96-007, Oct. 27, 1995).

4

The Economic Effects of Federal Spending on Infrastructure and Other Investments, 

Congressional Budget Office, June 1998; Road User and Mitigation Costs in Highway 

Pavement Projects, NCHRP Synthesis 269, Transportation Research Board, National 

Research Council, 1999.
Appendix II

Information About HERS Models

Page 31 GAO-01-299 Highway Infrastructure

Table 2: Key Differences Between the HERS Model and State-Level HERS Models

Model Feature Current HERS HERS-ST HERS/OR HERS/IN

Highway data 

sections 

considered

Analyzes a statistical 

sample of sections from the 

nation’s highways in 

FHWA’s nine highest 

highway classifications.

Analyzes a statistical 

sample of sections from 

state’s highways in FHWA’s 

nine highest highway 

classifications. State user 

can modify database to 

include data representing 

all state highways. 

Analyzes all highway 

sections in state highway 

system or a sample of 

sections.

Analyzes all highway 

sections in state highway 

system.

Cost of travel time Uses average national 

hourly compensation data 

to value travel time.

Uses average national 

hourly compensation data 

to value travel time. Allows 

state user to substitute 

state-level data for national 

data.

Allows user to substitute 

state-level data.

Allows user to substitute 

state-level data. Indiana 

DOT has not done so.

Highway 

improvement cost 

factors

Uses FHWA price index for 

federal-aid highway 

construction, adjusted to 

correspond to particular 

state. 

Uses FHWA price index for 

federal-aid highway 

construction, adjusted to 

correspond to particular 

state. Allows state user to 

substitute more specific 

state-level data for default 

values.

Allows user to substitute 

state-level data.

Uses state-specified 

pavement costs that differ 

from those in HERS.

Vehicle crash costs Uses updated analysis 

developed for FHWA’s 

1999 Conditions and 

Performance Report.

Uses updated analysis 

developed for FHWA’s 

1999 Conditions and 

Performance Report.

Uses older analysis 

developed for FHWA’s 

1997 Condition and 

Performance Report.

Uses updated analysis 

developed for FHWA’s 

1999 Conditions and 

Performance Report.

Air pollution 

damages

Uses information based on 

vehicle emissions data 

from Environmental 

Protection Agency’s 

MOBILE5a model.

Uses information based on 

vehicle emissions data 

from Environmental 

Protection Agency’s 

MOBILE5a model.

Does not address. Does not address. 

Price elasticity Uses rigorous approach to 

assess effect of changes in 

travel cost on drivers’ 

behavior. 

Uses rigorous approach to 

assess effect of changes in 

travel cost on drivers’ 

behavior. 

Uses rudimentary 

procedure to assess effect 

of changes in travel cost on 

drivers’ behavior.

Uses rudimentary 

procedure to assess effect 

of changes in travel cost on 

drivers’ behavior. 

Model output about 

improvements

Generates improvement 

cost data for each of nine 

highway classifications. 

Cost of individual sections 

is not reported.

Generates improvement 

cost data for each of nine 

highway classes and for 

each section.

Generates section-bysection report for each 

funding period, plus tables 

summarizing the state’s 

four highway 

classifications.

Generates section-bysection report, plus maps 

to illustrate improvements. 

Also creates tables of user 

benefits (travel time, 

operating cost, and safety).
Appendix II

Information About HERS Models

Page 32 GAO-01-299 Highway Infrastructure

User override mode Allows user to specify 

conditions under which 

improvements would be 

mandatory. This feature is 

not used for FHWA’s 

Conditions and 

Performance reports.

Allows user to specify type, 

cost, effect, and timing of 

an improvement.

Allows user to specify type 

and timing of an 

improvement for two 

funding periods.

Allows user to specify type, 

cost, effect, and timing of 

an improvement.

Model can analyze 

new highways

Does not allow user to 

specify new highway 

projects to be implemented 

in future years. 

Does not allow user to 

specify new highway 

projects to be implemented 

in future years. 

Does not allow user to 

specify new highway 

projects to be implemented 

in future years. 

Allows user to specify new 

highway projects to be 

implemented in future 

years. Indiana DOT has not 

done so.

(Continued From Previous Page)

Model Feature Current HERS HERS-ST HERS/OR HERS/IN
Page 33 GAO-01-299 Highway Infrastructure

Appendix III

Questionnaire for States That Asked to 

Participate in FHWA’s Pilot Program for the 

State HERS Model ApendxiI
Appendix III

Questionnaire for States That Asked to 

Participate in FHWA’s Pilot Program for the 

State HERS Model

Page 34 GAO-01-299 Highway Infrastructure
Appendix III

Questionnaire for States That Asked to 

Participate in FHWA’s Pilot Program for the 

State HERS Model

Page 35 GAO-01-299 Highway Infrastructure
Appendix III

Questionnaire for States That Asked to 

Participate in FHWA’s Pilot Program for the 

State HERS Model

Page 36 GAO-01-299 Highway Infrastructure
Page 37 GAO-01-299 Highway Infrastructure

Appendix IV

GAO Contacts and Staff Acknowledgments ApendxiIV

GAO Contacts Phyllis F. Scheinberg (202) 512-2834

Katherine Siggerud (202) 512-2834

Staff 

Acknowledgments

In addition to those named above, Richard Calhoon, Catherine Colwell, 

Timothy J. Guinane, Luann Moy, Judy K. Pagano, and Raymond Sendejas 

made key contributions to this report.

(348251) Letr

United States

General Accounting Office

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