U.S. DEPARTMENT OF THE TREASURY

Office of Economic Policy

April 2015

THE

D

EPARTMENT OF THE TREA

S

URY

1789

EXPANDING THE MARKET

FOR INFRASTRUCTURE 

PUBLIC-PRIVATE PARTNERSHIPS

ALTERNATIVE RISK AND PROFIT SHARING 

APPROACHES TO ALIGN SPONSOR AND 

INVESTOR INTERESTS
EXPANDING THE MARKET FOR INFRASTRUCTURE PUBLIC-PRIVATE PARTNERSHIPS:

ALTERNATIVE RISK AND PROFIT SHARING APPROACHES TO

ALIGN SPONSOR AND INVESTOR INTERESTS

U.S. DEPARTMENT OF THE TREASURY

Office of Economic Policy

April 2015

Abstract

Realizing the potential taxpayer benefits of public-private partnerships (PPPs) in infrastructure 

investment, including higher quality per dollar and faster project delivery, depends on allocating 

project risks to the party best able to manage them. Arguably, demand risk is the most important 

source of uncertainty affecting an infrastructure project’s financial viability, particularly in the 

case of new build, or “greenfield” projects in which the private partner’s compensation is 

determined by user volume, but for which no history of use exists. PPPs have typically used the 

basic user fee or availability payments models to allocate all demand risk and (therefore revenue 

risk) to either the private partner or the government, limiting the number of PPP deals that 

investors and project sponsors may find attractive. However, recent deals have migrated away 

from the basic user fee arrangement after several prominent PPPs using it encountered financial 

difficulty.

This paper presents three alternative incentive structures for PPP contracts that can potentially 

benefit both public sector sponsors, by delivering higher quality per dollar, and private investors, 

by generating attractive returns. The rate of return model, price cap model, and “sharing” model

all apply principles from the regulation of privately-owned energy and telecom infrastructure to 

PPP projects that generate user fees. In addition, these alternative risk- and profit-sharing

approaches may create choices that are attractive to investors and sponsors with risk preferences 

and return expectations not accommodated by more commonly used models. By expanding the 

options for sponsors and investors to consider in PPP negotiations, these incentive structures 

have the potential to increase the number of PPP deals and improve the odds of the projects’ 

long-term success.
1

I. Introduction

Infrastructure investment is critical to America’s continued economic success.1 Our nation must 

modernize and maintain our roads, bridges, and water systems to help ensure that the United 

States remains a place for businesses to operate productively and grow, which will, in turn, 

create economic opportunity for Americans. Yet years of underinvestment in our public 

infrastructure have imposed massive costs on our economy. Drivers in the United States 

annually spend 5.5 billion hours in traffic resulting in costs of $120 billion in fuel and lost time.2 

U.S. businesses pay $27 billion in additional freight costs because of the poor conditions of roads 

and other transportation infrastructure.3 Due to continuing deterioration of water systems 

throughout the United States, each year there are approximately 240,000 water main breaks 

resulting in property damage and repairs.4 Despite the high costs imposed by insufficient or 

decrepit infrastructure, outlays for both capital investment and operations and maintenance (as a 

percent of GDP) made by all levels of government in transportation and water infrastructure have 

declined in recent decades.5

The need to reverse years of underinvestment in infrastructure, despite tighter budgets at every 

level of government, calls for us to rethink how we pay for and manage infrastructure

investment. Some state and local governments have entered into public-private partnerships 

(PPPs) to provide and manage infrastructure that has traditionally been provided by the public 

sector. PPPs bring private sector capital and management expertise to the challenges of 

modernizing and more efficiently managing such infrastructure assets. Under a PPP, a 

government contracts with a private firm to design, finance, construct, operate, and maintain (or 

any subset of those roles) an infrastructure asset on behalf of the public sector. When the private 

sector takes on risks that it can manage more cost-effectively, a PPP may be able to save money 

for taxpayers and deliver higher quality or more reliable service over a shorter timeframe 

compared to traditional procurement. When sponsors contract with private partners that support 

strong labor standards, PPPs can also provide local economic opportunity and create good, 

middle-class jobs that benefit current and aspiring workers alike. Just as there is a range of roles 

that a private firm or firms can take on in a PPP, the nature of risk-sharing and compensation 

arrangements for bearing and managing risk can vary substantially from project to project and is 

 1 This paper was authored by Elaine Buckberg, Owen Kearney, and Neal Stolleman.

2 U.S. Executive Office of the President. National Economic Council and Council of Economic Advisers. 2014. 

An Economic Analysis of Transportation Infrastructure Investment. 

http://www.whitehouse.gov/sites/default/files/docs/economic_analysis_of_transportation_investments.pdf (accessed 

March 8, 2015).

3 Ibid.

4 “Aging Water Infrastructure.” Science Matters 1, no. 1 (2010). 

http://www.epa.gov/ORD/sciencematters/april2010/scinews_aging-water-infastructure.htm (accessed April 13, 

2015).

5 Bosworth, Barry and Sveta Milusheva. “Innovations in U.S. Infrastructure Financing: An Evaluation.” 

Presentation at the “Challenges for the Global Economy after the Tohuku Earthquake” Research Conference, Tokyo, 

Japan, November 7, 2011. http://www.nomurafoundation.or.jp/wordpress/wpcontent/uploads/2014/09/20111107_Barry_Bosworth-Sveta_Milusheva_000.pdf (accessed March 8, 2015).
2

governed by contract. Expanding the options for risk- and profit-sharing is the focus of this 

paper.6 

However, infrastructure — whether financed through traditional methods or PPPs — relies on 

funding sources to repay financing, whether debt, equity, or a combination. All infrastructure 

investments ultimately depend on either user fees, government tax revenues, or a combination of 

both. PPPs provide only financing and not funding. Therefore, community and political support 

for greater investment of government tax revenues or the imposition of user fees is critical to 

expanding investment in our nation’s public infrastructure.

While PPPs cannot eliminate the need for government spending on infrastructure, we can help

meet our nation’s infrastructure needs by expanding the sources of investment and using those 

dollars, whether public or private, as effectively as possible to advance the public’s interest. 

Other advanced economies, including Australia, Canada, and the United Kingdom, rely more 

heavily than the United States on PPPs to secure equity financing for infrastructure. This is due 

in part to the U.S. municipal debt market being the most developed of its kind in the world. 

Although the role of PPPs in the U.S. market is limited, the U.S. Department of the Treasury’s 

research and engagement with stakeholders indicate that significant private capital could be 

mobilized for infrastructure investment. However, in order to attract this capital, U.S. public 

infrastructure assets will have to support higher rates of return than are currently generated 

through 100 percent low-cost debt financing in the municipal bond market. The challenge is for 

PPPs to demonstrate overall cost savings and efficiencies that outweigh the lower-cost financing 

advantage of traditional procurement.

PPPs allow governments to introduce private sector capital into a project and also harness private 

sector management and technical expertise. When a PPP transfers risks to the private sector that 

it can manage more cost-effectively, it can benefit taxpayers by lowering long-term project costs, 

improving the quality of services, or both. Yet a PPP is not necessarily the best choice for every 

project, and governments can evaluate whether a PPP achieves the same outcome for lower 

overall costs compared to traditional procurement by using a “Value for Money” (VfM) analysis. 

Canada, for example, requires VfM analyses for all major infrastructure projects (i.e., having 

capital costs greater than $100 million) to determine whether it is more cost-effective to use PPP 

or conventional procurement.7

This paper presents new and alternative PPP incentive structures that can potentially align public 

and private sector interests in infrastructure provision and management, in contrast to the “basic 

user fee” (i.e., toll) and “availability payments” models, which historically have been used in 

PPPs and allocate all demand risk (and therefore, revenue risk) to either the private sector partner 

or the government. Recently, PPP deals in the United States have begun migrating away from 

 6 U.S. Department of the Treasury. Office of Economic Policy. 2014. Expanding Our Nation’s Infrastructure 

through Innovative Financing. http://www.treasury.gov/press-center/pressreleases/Documents/Expanding%20our%20Nation%27s%20Infrastructure%20through%20Innovative%20Financing

.pdf (accessed March 8, 2015). 7 VfM methodology involves: 1) creating a Public Sector Comparator (PSC), which estimates the lifecycle cost of 

carrying out the project through a traditional approach, 2) estimating the lifecycle cost of the PPP alternative, and 

3) completing an “apples-to-apples” comparison of the costs of the two approaches.
3

the basic user fee model, after several prominent PPPs using it encountered financial difficulty, 

and some recent projects have incorporated revenue-sharing.8 In order to increase awareness of

incentive arrangements that can be mutually beneficial for government sponsors and private 

investors, we draw upon incentive structures used in private industries that are regulated to 

protect the public interest — electric power, gas and oil pipelines, and telecoms — and apply 

them to PPPs. These industries have attracted substantial private investment flows while 

providing for demand risk to be shared between the government and the private sector.

9

This paper explains incentive structures that allow for profit-sharing. For example, the private 

partner may transfer a portion of its earnings directly to the government, thereby sharing with 

taxpayers, or the private partner’s cost savings may lower the price of using the infrastructure, 

sharing those savings with consumers. As extensions of the basic user fee model, these 

structures can enhance the private sector’s incentive to operate efficiently. By offering options 

that mitigate the demand risk borne by the private partner, these incentive structures may expand 

the scope for executing PPP deals. For example, some investors may be attracted by being able 

to share the project’s upside with the government in return for some protection from downside 

demand risk. In some states, including Texas, Florida, and New Jersey, PPP-enabling legislation

specifically provides for various types of sharing arrangements.10 The appropriate choice of 

model for any given project will depend on project specifics and the risk preferences of the 

project sponsor and investors.

The remainder of the paper is organized as follows: section II provides an overview of PPPs, 

section III presents three incentive structures for PPP contracts meant to expand the set of 

options beyond the basic user fee and availability payment models, and section IV concludes.

 8 For example, the Indiana Toll Road, Texas SH 130, and the South Bay Expressway in San Diego all experienced 

financial strain because actual demand turned out to be less than projected. See Mallet, William J. Indiana Toll 

Road Bankruptcy Chills Climate for Public-Private Partnerships (CRS Insights No. IN10156). Washington, DC: 

Congressional Research Service, 2014. http://www.ncppp.org/wp-content/uploads/2013/02/CRS-Insights-IndianaToll-Road-Bankruptcy-Chills-Climate-for-P3s.pdf (accessed March 9, 2015). 9 Various types of revenue- and profit-sharing mechanisms have been used in the regulated telecommunications, 

electricity, natural gas, and (in New York state only) water industries. See Sappington, David E. M. and Dennis L. 

Weisman. “Price Cap Regulation: What Have We Learned from 25 Years of Experience in the Telecommunications 

Industry?” Journal of Regulatory Economics 38, no. 3 (2010): 227-257; and The Brattle Group. “Alternative 

Regulation and Ratemaking Approaches for Water Companies,” September 30, 2013. 

http://www.nawc.org/uploads/documents-andpublications/documents/NAWC_Brattle_AltReg_Ratemaking_Approaches_102013.pdf (accessed March 8, 2015). 10 Under Florida’s PPP-enabling legislation, a negotiated portion of revenues from fee-generating uses must be 

returned to the public entity over the life of the agreement. See http://laws.flrules.org/2013/223

http://www.flsenate.gov/Session/Bill/2013/0085/BillText/er/PDF (accessed April 20, 2015). Under Texas PPP 

legislation, the responsible government entity may consider the opportunity for revenue-sharing as one of the project 

selection criteria, among other factors. See http://www.statutes.legis.state.tx.us/Docs/GV/htm/GV.2267.htm

(accessed April 20, 2015). The PPP between the Bayonne New Jersey Municipal Authority (BMUA) and Kohlberg 

Kravis Roberts & Co (KKR) was approved pursuant to the provisions of the "New Jersey Water Supply 

Privatization Act.” See http://www.nj.gov/dep/watersupply/pdf/statut_58.26-1.pdf (accessed March 12, 2015). The 

agreement incorporates revenue-sharing. See NW Financial Group, LLC. “Why the Bayonne Water/Wastewater 

Public-Private Partnership Succeeded,” April 1, 2013. http://www.nwfinancial.com/pdf/NW-BMUA-Report.pdf

(accessed April 14, 2015). 
4

II. Background on Public-Private Partnerships

PPPs as an alternative to traditional infrastructure procurement and management

Publicly-owned infrastructure assets are typically designed, constructed, operated, and 

maintained through “conventional procurement,” in which the sponsoring government owns the 

asset but separately contracts for each service, often from different private firms. Under 

conventional procurement, the government first contracts with a private entity to supply the

infrastructure design, then seeks bids to build the asset according to that design, likely from a 

separate firm, and finally, operates and maintains the infrastructure asset, or takes bids from yet 

another firm. With competitive bidding, this approach allows the public sector to have highly 

qualified private firms fulfill the requirements of various project phases; however, contracted 

parties do not have an incentive to minimize lifetime project costs, only costs incurred during 

their respective phases. 

Under a PPP, the government retains ownership of the infrastructure asset, while the private 

sector is afforded a much greater role in delivering and managing the asset compared to 

conventional procurement. This paper focuses on PPPs that transfer responsibilities for multiple 

phases of a project to the private partner. Consider a PPP where the government contracts with a 

private company to build or improve an infrastructure asset and to subsequently maintain and 

operate that asset for a number of years in exchange for a stream of revenue during the life of the 

contract, where the revenue stream will take the form of either user fees or availability 

payments.11 This contrasts with conventional procurement, as described above, in that the 

government is directly contracting with a single private entity or consortium to complete the 

various aspects of the project. As the single responsible party for multiple stages of the project, 

the private partner is then motivated to minimize costs across those project phases — an

incentive that is lacking under conventional procurement. Although the government owns the 

asset, many PPP contracts extend for 30 years or more, so that the private partner has control 

over a significant portion of the useful life of the asset. Finally, PPPs can vary in the extent to 

which they transfer responsibilities from the public to the private sector. 

A PPP requires dedicated revenue in order to be financially viable, whether from user fees or the 

government; a central consideration in structuring a PPP is which party will face uncertain

project revenue due to the unknown future demand for the infrastructure asset’s service. In the 

two basic models, the PPP places all demand risk (and therefore revenue risk, as well) with either 

the government or the private partner. In a basic user fee arrangement, the private partner 

collects and retains all fees from consumers of the service, e.g. bridge tolls and payments for 

water bills, and so bears all the risk of uncertain demand for the service. Alternatively, in an

availability payments model, the government sponsor collects any revenue from users and makes 

fixed, recurring payments to the private partner provided the asset meets contracted quality 

 11 See page 2 of Engel, Eduardo, Ronald D. Fischer, and Alexander Galetovic. The Economics of Public-Private 

Partnerships. New York: Cambridge University Press, 2014.
5

standards; because availability payments do not vary with asset use, the government bears all the 

demand and revenue risk.

12 

Recently, private investors in PPP projects have sought to reduce exposure to demand risk

following some troubled toll road PPP transactions.

13 As use of the basic user fee model has 

declined, the availability payment model has been adopted in an increasing percentage of U.S. 

PPPs, as illustrated by the chart below.

SOURCE: Allison, Peter. Welcoming remarks. Presentation at InfraAmericas US P3 Infrastructure Forum 2013, New York City, USA, June 18, 

2013.

Driven in part by the loss of the bond insurance markets and a newfound conservatism among 

senior debt lenders, project sponsors have also found new ways to structure PPPs to mitigate or 

retain risks that private investors no longer find acceptable.14 As shown in Table 1 below, a 

number of projects closed in the last three years incorporate revenue-sharing provisions.

 12 For example, assume that the government expects 100 cars per week to use a toll road, and that it will use the 

collected tolls from 100 cars to fund the weekly availability payment to the private partner. If only 20 cars use the 

toll road during a given week, the government must still pay the private firm the equivalent of the toll collections 

from 100 cars because the availability payment is a fixed obligation.

13 Mallet, William J. Indiana Toll Road Bankruptcy Chills Climate for Public-Private Partnerships (CRS Insights 

No. IN10156). Washington, DC: Congressional Research Service, 2014. http://www.ncppp.org/wpcontent/uploads/2013/02/CRS-Insights-Indiana-Toll-Road-Bankruptcy-Chills-Climate-for-P3s.pdf (accessed March 

9, 2015).

14 See U.S. Department of the Treasury. Office of Economic Policy. 2014. Expanding Our Nation’s Infrastructure 

through Innovative Financing. http://www.treasury.gov/press-center/pressreleases/Documents/Expanding%20our%20Nation%27s%20Infrastructure%20through%20Innovative%20Financing

.pdf (accessed March 8, 2015). Also see U.S. Department of Transportation. Federal Highway Administration. 

2010. Public-Private Partnership Concessions for Highway Projects: A Primer. 

http://www.fhwa.dot.gov/ipd/pdfs/p3/p3_concession_primer.pdf (accessed March 11, 2015). If performance 

standards are not met, availability payments can be reduced or eliminated.
6

Table 1: U.S. PPP Deals, April 2012-April 2015

Financial 

Close

Amount 

Project Sector ($mil.) Incentive Structure15

Midtown Tunnel Transport 2012 2,100 Revenue-sharing

Presidio Parkway Doyle Drive Concession Transport 2012 362 Availability payments

I-95 HOV/HOT Lanes Transport 2012 923 Revenue-sharing

I-95 North, SR 406 to SR 44, Transport 2012 118 Availability payments

SR 9B Extension - Duval County Transport 2012 95 Availability payments

Maryland I-95 Travel Plazas Redevelopment Transport 2012 56 Revenue-sharing

I-75 Expansion Transport 2012 72 Availability payments

Rialto Water System Water 2012 172 Revenue-sharing

Bayonne Water & Wastewater Concession Water 2012 173 Revenue-sharing

Carlsbad Seawater Desalination Plant Water 2012 903 Availability payments

Ohio River Bridges Project - East End Crossing Transport 2013 763 Availability payments

North Tarrant Expressway Segments 3A, 3B Transport 2013 1,350 Revenue-sharing

Goethals Bridge Transport 2013 1500 Availability payments

Georgia Northwest Corridor (NWC) Transport 2013 840 Basic user fees

US 36 Transport 2014 120 Revenue-sharing

I-69 Transport 2014 370 Availability payments

I-4 Ultimate Transport 2014 2300 Availability payments

SH 183 - Dallas-Fort Worth (Gap Financing) Transport 2014 848 Revenue-sharing

Pennsylvania Bridges Project Transport 2015 900 Availability payments

Southern Ohio Veterans Highway Transport 2015 553 Availability payments

Sources: InfraDeals and project descriptions from state departments of transportation and concession agreements. 

Benefits of PPPs

By providing incentives to the private partner to minimize costs across project stages, while also 

requiring that stipulated quality standards be satisfied, a PPP can lower costs over the life of the 

asset, lower the cost of using the asset by improving quality of service, and reduce the time until 

the project is complete and operational. These incentives arise because the PPP contract both 

holds the private partner responsible for paying the unknown future costs of completing various 

project phases, and endows the private partner with full decision-making power and control of 

the asset in completing those phases. In other words, a PPP relies on transferring risks from the 

public to the private sector in order to ultimately realize efficiency gains.

 15 Projects categorized as “Basic user fees” collect user fees but their contracts do not include any sharing 

provisions. The projects categorized as “Revenue-sharing” also collect user fees, but their contracts generally 

stipulate that project revenues are shared between the public sponsor and the private partner in some fashion. In 

contrast to the basic use fee model, under the revenue-sharing model, the private partner does not bear all of the 

demand risk (and therefore not all of the revenue risk, either). These revenue-sharing structures may include some 

but not all of the elements of the incentive structures described in section III. 
7

Mandating quality standards is important because a PPP incentivizes cost-cutting. Consumers 

care about both cost and quality; cost-cutting becomes undesirable if it results in unacceptably

lower quality of the infrastructure asset and the service that it provides. Quality is “contractible” 

if the stipulated level of quality can be translated into contractual terms and readily verified by 

the government and the private party. Given the importance of contractible quality for potential 

efficiency gains through PPPs, whether or not quality is contractible carries implications for 

which types of infrastructure projects are appropriate for PPPs. In instances where quality is not 

contractible, a PPP contract is more likely to induce the private partner to cut costs in ways that 

result in suboptimal quality of the infrastructure service.16 

Because a PPP incentivizes cost-cutting, some private partners may seek to reduce labor costs by 

lowering wages. Lowering wages for workers on a project may reduce costs but it does not 

create additional value for taxpayers. On the contrary, cutting wages is likely to reduce the 

quality of labor. Requiring strong labor standards is one strategy to ensure that the cost 

reductions from PPPs are not achieved simply through wage reductions. 

By both transferring risk and imposing verifiable quality standards, a PPP contract can induce 

efficiency-increasing reductions in cost via two avenues: 

1. “Bundling” responsibility for multiple project phases incentivizes the private partner 

to capture cost savings across phases, such as by making long-view investment choices in 

earlier phases of the project that reduce costs in later phases. For example, using higher 

quality but more expensive paving material on a road might prevent potholes and reduce 

maintenance costs. In conventional procurement, such incentives are absent because

different parties are typically responsible for the construction and maintenance phases.17 

Bundling can also encourage accelerated project delivery; if the private partner is 

responsible for the construction, operation, and financing of the project, and receives a 

share of project revenues, then it will have increased incentives to complete construction 

and begin operation as early as possible in order to start providing a return to both debt 

and equity investors.

 

2. Contractually obligating the private partner to meet minimum asset and service 

quality standards can improve efficiency and produce further cost savings. Minimum 

standards can prevent the deferral of maintenance and resulting asset deterioration, 

 16 In some situations where it is not possible to contract output quality directly, it might still be possible to do so 

indirectly by stipulating quality standards for the inputs. This is only effective, however, if the choice of inputs 

determines the quality of the output in a predictable way known by the project sponsor. Also, selection of inputs by 

the government precludes the private partner from using its technical and managerial expertise to choose the 

efficient mix of inputs. In these cases, a PPP may not be the best choice for organizing the project.

17 For discussions of why the government might have difficulty achieving cost savings across project phases on its 

own, see Hall, John. “Private Opportunity, Public Benefit?” Fiscal Studies 19, no. 2 (1998): 121-140; and Engel, 

Eduardo, Ronald D. Fischer, and Alexander Galetovic. “Public-Private Partnerships: When and How.” Working 

paper, Yale University (2008). 

http://www.econ.uchile.cl/uploads/publicacion/c9b9ea69d84d4c93714c2d3b2d5982a5ca0a67d7.pdf (accessed 

March 12, 2015).
8

therefore lowering the costs to users imposed by a degraded asset (e.g. potholes on a road 

increase vehicle wear-and-tear).

Finally, the government may not realize the potential cost savings from a PPP discussed above if 

the procurement process is not competitive or if contract renegotiations resulting in additional 

reimbursement from the government to the private partner are prevalent. The possibility of 

successful renegotiation by the contract awardee induces “moral hazard”: if the concessionaire 

believes that it can extract additional payments from the sponsor to cover its higher costs, then 

the incentive for cutting costs is blunted. While the benefit of setting minimum contractual 

quality standards is not unique to PPPs, it is particularly relevant for the long-term transfer of 

responsibility.

Risk and risk transfer in PPP contracts 

The chief mechanism for realizing cost savings in a PPP, bundling, requires the transfer of 

multiple project risks from the public to the private sector. 18 Under conventional procurement, 

taxpayers bear most of the risks identified in Table 2 below, even those risks that the government 

is not well-positioned to influence.

19,20 The net benefit from PPP procurement is maximized 

when 1) a given controllable risk is allocated, and the related decision-making authority is 

delegated, to the party that can best influence it, and 2) any risk that no party can control is 

allocated to the party that is best able to manage or diversify it.

21 

 18 The term “bundling” can also have another meaning in the context of PPPs: “...contracting with one partner to 

provide several small-scale PPP projects in order to reduce the length of the procurement process as well as 

transaction costs.” See page 17 of Deloitte Research. “Closing America’s Infrastructure Gap: The Role of PublicPrivate Partnerships,” 2007. 

http://worldbank.mrooms.net/file.php/251/docs/optional_readings/Closing_America_s_Infrastructure_Gap.pdf

(accessed April 13, 2015). 

19 An exception is performance risk, which is borne by users. 20 This even includes the risk of construction cost overruns — which are borne by the construction company under 

the actual contract — if contract renegotiations are commonplace. See Engel, Eduardo, Ronald D. Fischer, and 

Alexander Galetovic. The Economics of Public-Private Partnerships. New York: Cambridge University Press, 

2014.

21 A party more effectively manages a risk that cannot be directly controlled when it minimizes the expected dollar 

impact conditional on bad outcomes occurring, minimizes the probability of bad outcomes, or both.
9

Table 2: Major Risks in an Infrastructure Project22

In general, as the number of related risks that can be appropriately transferred to the private 

partner increases, the incentives for cost saving are strengthened. For example, the “designbuild” (DB) contract transfers both design and construction risk, which incentivizes the private 

partner to design the project so as to minimize building costs and the likelihood of design 

flaws.23 The “design-build-operate-maintain” (DBOM) model additionally encourages the 

private partner to select building methods and materials that minimize operations and 

maintenance costs, while the “design-build-finance-operate-maintain” (DBFOM) structure also 

incentivizes the private partner to reach the operations phase as early as possible to begin paying 

back investors. Performance risk is also transferred from users to the private partner when the 

PPP contract sets quality standards for the infrastructure assets and services. 

Some risks to private investors in a PPP are in the public sector’s control: for example, a local

government could construct a non-tolled road competing for the same users as an existing PPP 

toll road.24 Flexible contracts can minimize the need for renegotiation in these cases. Including 

adaptable competition clauses can help preserve the government’s ability to build competing 

projects that are in the public interest while providing protections to investors. For example, 

Florida’s PPP-enabling legislation for transportation facilities specifically requires that, among 

other things, proposed projects must have adequate safeguards in place to ensure that the Florida 

Department of Transportation has the opportunity to add capacity serving similar origins and 

 22 The categorization of risks in Table 2 follows, in part, the discussion in Engel, Eduardo, Ronald D. Fischer, and 

Alexander Galetovic. The Economics of Public-Private Partnerships. New York: Cambridge University Press, 

2014.

23 In addition, project delivery time may be shortened compared to conventional procurement because of better 

coordination between the design and build functions.

24 In some cases, state-specific PPP legislation may restrict the flexibility of PPP contracts, e.g. in Arizona and 

North Carolina, the public sector is required to maintain comparable non-tolled roads when it establishes new toll 

roads. Also, there are prohibitions against non-compete clauses in Alabama, Florida, Mississippi, North Carolina 

and Texas. See Appendix B of National Conference of State Legislatures. “Public-Private Partnerships for 

Transportation: A Toolkit for Legislators,” October 2010. 

http://www.ncsl.org/documents/transportation/PPPTOOLKIT.pdf (accessed March 9, 2015).

Risk Category Examples of (Downside) Risks

Design  Design flaws

 Construction cost overruns

 Delays to completion

 Higher operations costs

 Higher maintenance costs

 Periods of service unavailability

 Lower service quality

Policy  New competing capacity

Demand  Lower utilization than initially forecasted

 Higher interest rates

 Less favorable exchange rates

Construction

Operations and 

Maintenance

Performance

Financial
10

destinations; having this type of flexibility is especially important if, for example, persistent 

congestion develops on the privately operated facility.

25

When user fees comprise the entirety of the private party’s revenue stream, demand risk is likely

the central determinant of the PPP’s financial viability. While all projects are subject to 

uncertainty regarding future utilization, demand forecasts for so-called greenfield projects are 

particularly unreliable because there is no past usage baseline.26 According to the World 

Economic Forum, excessively positive forecasts have been common in PPP road projects.

27 Not 

coincidentally, a number of road PPP projects have entered bankruptcy.

28

Demand risk differs from other risks that can be beneficially transferred to the private partner —

such as design, construction, operations and maintenance, performance — in that the private 

partner’s actions can do little to influence the risk. Yet, as with the models presented in the next 

section, exposing the private partner to some (if not necessarily all) demand risk might attract 

potential investors looking for upside potential not possible under an availability payments 

arrangement (in which they would be completely insulated from demand risk).

III. Innovative Revenue, Profit, and Risk-sharing Arrangements for 

Infrastructure Provision

Discussions of PPPs in the United States have often focused on user fee or availability payment 

agreements, where either the private partner or the government sponsor bears all of the demand 

risk (and therefore all of the revenue risk, as well).

29 Following the financial difficulties of some 

user fee toll road projects, private investors have looked increasingly to the availability payments 

model to reduce exposure to revenue volatility.

30 Project sponsors have also found new ways to 

 25 The legislation states that, before approval, the Department of Transportation must determine that the proposed 

project “would have adequate safeguards in place to ensure that the department or the private entity has the 

opportunity to add capacity to the proposed project and other transportation facilities serving similar origins and 

destinations.” See 

http://www.leg.state.fl.us/Statutes/index.cfm?App_mode=Display_Statute&Search_String=&URL=0300-

0399/0334/Sections/0334.30.html (accessed March 30, 2015). 26 A “greenfield” PPP infrastructure project is one in which the private partner designs and constructs a brand new 

infrastructure asset, and may operate it, depending on the specifics of the PPP arrangement. In a “brownfield” 

project, the private partner assumes temporary control of an existing asset for purposes of upgrading its capacity 

and/or quality, and may also operate it. 27 World Economic Forum. “Strategic Infrastructure – Steps to Prepare and Accelerate Public-Private Partnerships,” 

May 2013. http://www3.weforum.org/docs/AF13/WEF_AF13_Strategic_Infrastructure_Initiative.pdf (accessed 

March 8, 2015).

28 Dezember, Ryan and Emily Glaser. “Drop in Traffic Takes Toll on Investors in Private Roads.” Wall Street 

Journal, November 20, 2013.

29 See, for example, Sobel, Patrick and Robert Puentes. “Private Capital, Public Good — Drivers of Successful 

Infrastructure Public-Private Partnerships.” Brookings Institution, (2015). 

http://www.brookings.edu/research/reports2/2014/12/17-infrastructure-public-private-partnerships-sabol-puentes

(accessed April 17, 2015). 

30 Mallet, William J. Indiana Toll Road Bankruptcy Chills Climate for Public-Private Partnerships (CRS Insights 

No. IN10156). Washington, DC: Congressional Research Service, 2014. http://www.ncppp.org/wp-
11

structure PPPs to mitigate or retain risks that many private investors no longer find acceptable, 

including introducing revenue-sharing. The allocation of demand risk, therefore, need not be 

limited to user fees or availability payments. 

By further broadening the scope for PPP negotiations beyond the two basic models, this paper 

aims to increase the likelihood that potential partners will find a mutually agreeable structure that

aligns public and private interests in infrastructure provision and operation. The remainder of 

this paper discusses three alternative incentive structures for PPP contracts that may help 

partners reach agreement and align interests. Which structure, including the basic models, is 

most suitable for a given project, will depend on the specifics of that project and the risk 

preferences of the project sponsor and investors. The frameworks discussed in this paper are 

formulated in terms of a single price for an infrastructure service, such as a toll per vehicle on a 

highway or rate per gallon of water consumed. However, the concepts are equally applicable to 

multiple prices within a given infrastructure service, such as variable rate tolling for managing 

demand and reducing congestion on highways.

In brief, the three alternative models are as follows: 

• Rate of return model: The rate of return model balances consumer and investor interests

by placing a limit directly on the allowed rate of return on investment, and setting a 

regulated price that generates the revenue the firm anticipates it will require to cover its 

expected costs and earn the designated return. The regulated price can be adjusted at set 

intervals so that the firm earns the designated rate of return. The regulated price will be 

increased if, for example, the actual rate of return falls short of the designated rate, where 

the time between price adjustments carries implications for risk-sharing and the incentive

to operate efficiently. For instance, a long wait until the price can increase places more 

of the demand risk on the private firm while providing a strong incentive to hold down

costs; conversely, a shorter wait until the price can increase places less of the demand risk 

on the private firm and provides less incentive to lower costs.

• Price cap model: A variation of the basic user fee model, the price cap model balances

consumer and investor interests by limiting the price of the infrastructure service instead 

of the rate of return. Since profits are not directly constrained, there is a powerful 

incentive to minimize costs; also, the private firm assumes all demand risk because price

cannot be increased in response to a demand shortfall. Under this model, the maximum 

price increases each year by the rate of inflation minus the expected rate of improvement 

in the firm’s productivity, which achieves a balance between the public and private sector 

by compensating the firm for higher nominal input costs, while allowing consumers to 

benefit from anticipated productivity gains (the private firm retains all gains from 

productivity improvement in the basic user fee model). The built-in expected 

productivity assumption provides an added efficiency incentive because the firm is able 

to retain productivity gains in excess of projections; the expected productivity assumption

can be varied periodically to keep it aligned with changes in actual performance.

 

content/uploads/2013/02/CRS-Insights-Indiana-Toll-Road-Bankruptcy-Chills-Climate-for-P3s.pdf (accessed March 

9, 2015). 
12

• Sharing models: Contracts with profit-sharing can directly align sponsor and investor 

interests. For example, if the project exceeds or falls short of negotiated threshold rates

of return, the partners can either share the excess return or absorb the shortfall in 

contractually defined proportions. This type of flexibility expands the universe of 

acceptable deals because investors may be more willing to enter into an agreement where 

they are required to share the project’s upside potential with the government if the public 

sector, in turn, provides some protection from demand risk on the downside.

The rate of return and price cap models adopt principles used in public utility regulation, 

including the energy and telecom industries, where infrastructure assets are privately owned and 

regulation is used to protect taxpayer and customer interests while allowing reasonable profits.31

Different forms of profit- or revenue-sharing have also been incorporated into the regulation of 

energy, water, and telecommunications sectors, as well as in some highway and water PPP 

projects. 

The alternative incentive structures discussed below could be implemented by incorporating key 

characteristics of the contract into the competitive bidding process widely used to award PPP 

contracts.

32 For example, the public sponsor, with the assistance of outside financial experts, 

could define the structure of the desired contract, and private firms vying for the project would 

bid on the specific contractual elements, such as their preferred sharing percentages or demand 

and rate of return thresholds.33 Similar processes are used in the energy and telecom industries, 

where regulators set the allowable rate of return after evaluating cost and demand information 

supplied by the public utility as part of the rate-setting process. In the context of a PPP 

transaction, the public sponsor would evaluate the bids, selecting the bidder most likely to 

deliver the project at the lowest lifecycle cost while meeting quality standards, thus maximizing 

value for taxpayers. Incorporating these additional elements should not impose onerous 

information requirements on bidders, since much of the required data would be needed for bid 

preparation in any event.34

In the remainder of this section, we provide a conceptual overview of the three incentive 

structures which can be applied in PPP projects where user fees can be collected, quality 

standards are contractible, and provision of the infrastructure service is characterized by 

 31 In public utility regulation, the “reasonableness” of profits generally is determined by regulators. 32 Engel, Eduardo, Ronald D. Fischer, and Alexander Galetovic. “Public-Private Partnerships: When and How.” 

Working paper, Yale University (2008). 

http://www.econ.uchile.cl/uploads/publicacion/c9b9ea69d84d4c93714c2d3b2d5982a5ca0a67d7.pdf (accessed 

March 12, 2015).

33 The agreed upon values for specific contract elements will depend on the specific project; demand uncertainty is 

greater for a new greenfield project compared to a brownfield project where existing assets with a documented 

history of demand are temporarily transferred to the private partner. 34 To take a hypothetical example, if the public sponsor, after consulting with outside financial experts, specifies the 

contract will include a rate of return threshold of X% and that the sponsor will absorb Y% of any return shortfall, 

then private firms will simply submit bids on the minimum values of X and Y they are willing to accept, and the 

sponsor will select from among these. The logical structure of contract terms would be straightforward to 

implement. 
13

economies of scale.

35 We review each model in terms of the incentives it provides for cost 

efficiency, technical innovation, and service quality during the project’s operational phase, and 

how demand risk and operations and maintenance risk are allocated between the public and 

private partners.

36

1. Rate of return model: A regulated price that covers costs and provides a return

The rate-base rate of return model has been a cornerstone of public utility regulation in the 

United States since the early 1900s and has been widely used at both the federal and state levels 

to regulate privately-owned, public utilities such as electricity transmission, oil and gas pipelines, 

telecommunications, and water utilities, for which there is little or no competition by design. For 

example, the Federal Energy Regulatory Commission (FERC) is responsible for regulating the 

rates that interstate oil and natural gas pipelines charge for transportation, while individual state 

public utility commissions (PUCs) regulate the local distribution companies. 

The rate of return model protects consumers from excessive rates by setting a regulated price that 

approximates what the price would be if the utility had to compete with similar firms instead of 

operating as a monopoly franchise.37 At the same time, the price is calculated to explicitly allow 

the private firm to recover its costs and earn a return on its “rate base,” which essentially is the 

value of fixed assets used to produce the infrastructure service.38 Although the rate of return 

model has primarily been used to regulate private firms, we propose that the model offers similar 

protection to consumers of infrastructure services that exhibit natural monopoly characteristics or 

that are otherwise imperfectly competitive. Infrastructure project sponsors and private partners 

can agree to adopt a rate of return model by incorporating its salient features in a PPP contract.

How does the rate of return model work? 

This simple formula illustrates how the allowable price is determined.

AAAAAAAAA pppp =

O O OO & m e + d + + ( × o r )

D

 35 Economies of scale means that a firm’s output can be doubled for less than a doubling of cost. This often arises in 

large-scale infrastructure projects because a high proportion of total costs are fixed, meaning they do not vary with 

the level of output. The result is that the average cost of producing an additional unit of output falls as output 

increases.

36 In situations where user fees cannot be collected or where quality standards are not contractible, conventional 

public provision of infrastructure may be more appropriate than public-private partnerships. 37 Large-scale infrastructure is characterized by high fixed costs, e.g. transmission lines and towers for electricity 

supply or pipelines for gas and water supply, giving rise to economies of scale (because most costs are fixed and the 

firm’s output can double, for example, for less than a doubling of cost). Firms characterized by this type of 

production are called natural monopolies, because one firm can produce the entire output of the market at a cost 

lower than what it would be if there were several firms. 

38 The rate of return is sometimes defined as a weighted average cost of capital, consisting of the cost of debt and the 

return on equity, where the weights are the shares of debt and equity in the capital structure.
14

The terms in the numerator add up to the “revenue requirement,” i.e., the amount of money the 

firm expects it will need per time period (often a year) to cover operating expenses, capital costs, 

and taxes, while also earning a “fair” return on its rate base that is adequate to attract private 

capital. The concept of a “fair” return in the context of public utility regulation may include 

considerations such as whether the return 1) is sufficient to maintain the firm’s financial 

viability, 2) enables the utility to attract additional capital, and 3) is comparable to the return 

earned by other companies with similar risks.39 The denominator is the expected level of 

demand for the infrastructure service during the same time period, e.g. the annual number of 

gallons of drinking water consumed or projected number of vehicles traveling on a toll road. 

The ratio is the allowable price per unit, i.e. the price per gallon of water or toll charged per 

vehicle. Multiplying the allowable price by expected demand at that price yields the revenue 

requirement needed to cover costs and provide the designated return.

Regulators set the allowable rate of return after evaluating cost and demand information supplied 

by the public utility as part of an extensive rate-setting process that can involve testimony of 

expert witnesses for both the regulator and public utility.

40 In a PPP transaction, competitive 

bids would include supporting information about cost, demand, and the rate of return, and would 

be reviewed as part of the contract negotiations between the public sponsor and winning bidder.

In practice, the realized rate of return may differ from the rate assumed in the regulatory process. 

Rate of return regulation offers the public utility a fair opportunity, but not an ironclad 

guarantee, to earn its weighted average cost of capital; the regulated firm — or PPP — still has to 

contend with demand risk and operations and maintenance cost risk. For example, if actual 

water consumption and the costs of operating water treatment plants match the baseline 

assumptions used to set the allowable price, then the private firm will earn the designated rate of 

return. But if actual demand or costs differ from the baseline assumptions, then the realized rate 

will either fall short of or exceed the expected return until the allowable price is adjusted, either 

at the next scheduled rate hearing or by a short-term revenue stabilization measure implemented 

by the regulator.41 The graph below illustrates these points using hypothetical data. The red line 

illustrates demand risk: with per unit operations and maintenance costs at the expected level, the 

rate of return varies with realized demand. For a given level of demand, operations and 

maintenance cost risk is illustrated by the two lines that are parallel to the red line: the rate of 

 39 See page 436 of Madden, Sean P. “Takings Clause Analysis of Utility Ratemaking Decisions: Measuring Hope’s 

Investor Interest Factor.” Fordham Law Review 58, no. 3 (1989): 427-446. Also see page 42 of Regulatory 

Assistance Project. “Electricity Regulation in the U.S.: A Guide,” March 2011. See also 

www.raponline.org/docs/RAP_Lazar_ElectricityRegulationInTheUS_Guide_2011_03.pdf (accessed March 11, 

2015). The Regulatory Assistance Project report cites Federal Power Commission vs. Hope Natural Gas Company 

and Bluefield Water Works and Improvement Company vs. Public Service Commission, 262 U.S. 679 (1923) as two 

key Supreme Court cases setting out general criteria that public utility commissions must follow when setting rates 

of return.

40 In practice, public utility regulators use either historical data, projections for a future test year, or a combination to 

obtain cost and demand information for computing the regulated price. For greenfield PPPs, the allowable price 

would necessarily be based on projections, while for brownfield PPPs, it would incorporate historical data. 

41 See The Brattle Group. “Alternative Regulation and Ratemaking Approaches for Water Companies,” September 

30, 2013. http://www.nawc.org/uploads/documents-andpublications/documents/NAWC_Brattle_AltReg_Ratemaking_Approaches_102013.pdf (accessed March 8, 2015).
15

return is lower than expected if per unit costs are higher than expected (blue line) or the rate of 

return is higher than expected if per units costs are lower than expected (green line). 

The private partner’s incentive to operate in the most cost-efficient manner will be affected by 

how quickly the allowable price is adjusted when the actual rate of return differs from the target 

rate.42 For example, if the contract allows higher costs to be quickly translated into higher 

prices, then the firm’s incentive to hold down costs will be blunted. Similarly, the firm’s 

incentive to use innovative cost-saving technology will be weakened if operational cost savings 

are swiftly reflected in lower prices.

By contrast, a PPP contract that constrains prices to adjust less frequently strengthens incentives 

for management to operate the project efficiently because the firm either has to absorb a portion 

of cost increases or can keep earnings from superior performance.

43 Negotiating this type of 

adjustment provision in a PPP contract requires the public and private entities to balance their 

interests in a way that has the potential to maximize expected long-term benefits for everyone. 

 42 As mentioned earlier, there may be multiple prices for a single infrastructure service: for example, a public transit 

system might have reduced fares for seniors and/or students. A PPP contract may be designed to limit or exempt 

certain population segments, such as seniors, from price increases. 43 See Ofwat. 2007. New Approaches to Expenditures and Incentives. 

http://www.ofwat.gov.uk/pricereview/pr09phase1/pap_con_apprchexpincent.pdf?download=Download# (accessed 

March 8, 2015). In the regulated UK water industry, if companies can deliver outputs with lower capital or 

operating expenditure than assumed, prices are lowered, but only after five years in order to provide incentives to 

reduce costs. The regulator also monitors delivery of outputs to make sure cost reductions are due to efficiency 

improvements and not due to failure to deliver services at acceptable quality levels. Quality monitoring needs to be 

an important part of PPP contracts, as discussed in Sections II and III.3. 
16

The frequency of price adjustment for deviations in demand from baseline assumptions also 

determines to what extent the public or private partner bears the project’s demand risk. If 

utilization of a PPP toll road falls short of projections because more drivers use a nearby nontolled road, the arrangement requires that the allowable toll is increased so that the firm achieves

its target rate of return. For regulated gas and electric utilities, annual adjustments are relatively 

common. Regulated utilities sometimes use “decoupling” to annually adjust rates and stabilize 

revenues in the time period between formal rate cases, which can be up to three years, depending 

on the state (annual rate adjustments that are made to stabilize revenue are referred to as “trueups”).

44 The negotiated frequency of price adjustment in a PPP contract must balance the public 

interest in avoiding sharp toll hikes with the private sector’s need for a financially viable 

project.45 

The magnitude of the price adjustment needed to restore the allowable rate of return depends in 

part on the price elasticity of demand, i.e. the responsiveness of demand to a price change.46 

Demand responsiveness tends to be low for infrastructure services because, in general, there are 

few substitutes readily available to consumers. However, availability of even an imperfect 

substitute will require a larger price increase in order to make up for the loss of users who shift to 

a nearby non-tolled but highly congested road. 

Price Adjustment Frequency and Risk Allocation 

 44 Eto, Joseph, Steven Stoft, and Timothy Belden. “The Theory and Practice of Decoupling Utility Revenues from 

Sales.” Utilities Policy 6, no. 1 (1997): 43-55. 45 For example, in the regulated UK water industry, if companies can deliver outputs with lower capital or operating 

expenditure than assumed, prices are lowered, but only after five years in order to provide incentives to reduce costs. 

In telecommunications, rate case moratoriums are sometimes implemented to guarantee the regulated firm that 

profits made at current prices will not be taken away. This process imposes a regulatory lag, typically 2-5 years, 

intended encourage the regulated firm to reduce operating costs (i.e., the firm will be able to retain the resulting 

increase in earnings). Similar provisions can be written into PPP contracts. 46 The price elasticity of demand is defined as the percentage change in quantity demanded of a good resulting from 

a one-percent increase in its price.
17

Summary

The rate of return model sets a regulated price that allows the private firm to recover its costs and 

earn a designated return on its “rate base.” In the case of a PPP, the project sponsors and their 

private partners can agree to adopt a rate of return model by incorporating it in a PPP contract. If 

actual demand and costs differ from the baseline assumptions, the price will be adjusted to 

enable the firm to earn its allowed rate of return. This feature provides the firm with greater 

protection against demand risk than does the basic user fee model; it also affords better 

protection against operations and maintenance cost risk than the user fee and availability 

payments models. However, the rate of return model provides somewhat less incentive for cost 

cutting than user fee and availability payment contracts because price is eventually reduced to 

reflect cost savings or eventually raised to reflect cost increases. As the frequency of price 

adjustments increases, the incentives for cost efficiency weaken. 

2. Price cap model: The real price is adjusted for efficiency gains

The price cap model protects consumers from the possibility of excessive price increases but, in 

contrast to the rate of return model, it does so by setting limits directly on the price of an

infrastructure service, not on the rate of return. Since the focus of regulatory control is on prices 

and not on profitability, private firms have a powerful incentive to minimize costs and improve 

productivity performance in order to increase their profitability.

Price cap regulation has been used in the United Kingdom since the late 1980s and now applies

to all of the privatized British network utilities.47 In the United States, price cap regulation 

began replacing rate of return regulation in portions of the telecommunications sector in 1989

and is now used in most states as well as in interstate telecommunications regulation; price caps 

are also used in many other telecommunication markets throughout the world. 48,49 Other 

countries use price cap regulation beyond telecommunications, e.g., Australia (energy and 

transport) and France (postal service).50,51

 47 Green, Robert. “Has Price Cap Regulation of UK Utilities Been A Success?” Public Policy for the Private Sector

132 (1997). http://siteresources.worldbank.org/EXTFINANCIALSECTOR/Resources/282884-

1303327122200/132green.pdf (accessed March 11, 2015). 48 Blackman, Colin and Lara Srivastava, editors. Telecommunications Regulation Handbook. Washington, DC:The 

International Bank for Reconstruction and Development / The World Bank, InfoDev, and the International 

Telecommunications Union, 2011. 

https://openknowledge.worldbank.org/bitstream/handle/10986/13277/74543.pdf?sequence=1 (accessed March 12, 

2015).

49 Sappington, David E. M. and Dennis L. Weisman. “Price Cap Regulation: What Have We Learned from 25 

Years of Experience in the Telecommunications Industry?” Journal of Regulatory Economics 38, no. 3 (2010): 227-

257.

50 King, Stephen P. “Principles of Price Cap Regulation,” In Infrastructure Regulation and Market Reform: 

Principles and Practice, edited by Margaret Arblaster and Mark Jamison, 46-54. Canberra: Australian Competition 

and Consumer Commission and Public Utility Research Centre, 1998.

51 Reisner, Robert A.F. “Price Caps and the U.S. Postal Service: Prospects, Perils and the Public Interest.” Paper 

prepared for the President’s Commission on the U.S. Postal Service, Global Insight (2003). 

http://govinfo.library.unt.edu/usps/offices/domestic-finance/usps/docs/may_26_paper3.pdf (accessed March 12, 

2015).
18

How does the price cap model work?

For public utilities subject to price cap regulation, an initial price is often calibrated such that the 

firm can cover its costs and earn a fair return, similar to the rate of return model. In a PPP 

contract, the initial rate of return and price would be negotiated between the private partner and 

project sponsor as part of the competitive bidding process used to award the PPP. From that 

point forward, as in public utility regulation, the maximum allowable price, or cap, would be

allowed to increase at a rate tied to, but below, inflation (as measured, for example, by the 

Consumer Price Index (CPI), and expressed as a proportion): 

AAAAAAAAA pppp h y = AAAAAAAAA pppp y × (1 + CCC − )

where x, the so-called “x-factor”, is the expected rate of improvement in the firm’s productivity 

over the operational phase of the project.52 For instance, the output of a bridge — the rate of 

traffic flow per year — might be increased by adjusting the inputs used to provide the service, 

e.g. upgrading to real-time, automated toll collection facilities or by installing traffic congestion 

management technology on approaches to the bridge. The x-factor measures by how much the 

growth of the firm’s output is expected to outpace the growth of its inputs over the course of the 

project’s operation. 

The rationale for this approach is that while price should be allowed to increase with inflation to 

compensate the firm for higher input costs due to increases in the overall level of prices in the 

economy, slowing the annual rate of appreciation by subtracting x allows consumers to benefit 

from the firm’s expected productivity improvement.53 Put another way, the x-factor pares back 

the rate by which the price is adjusted to reflect inflation. Regulators also may allow a firm to 

adjust prices in response to factors beyond its control (via the “z-factor”), which can be a 

positive or negative adjustment.54

 52 The calculation of “x” can be based on the average productivity improvement that has been observed for similar 

firms, domestically or internationally. In a PPP contract, information developed as part of bid preparation and value 

for money analysis can be used to estimate the “x-factor” over the operational phase of the project, because these 

studies estimate project performance over the life of the contract. 

53 Some user fee and availability payments contracts include inflation adjustments and other economic factors but do 

not include an offset for the firm’s expected productivity performance. 

54 The z-factor should reflect cost elements that are beyond the control of the regulated firm and that have a 

pronounced financial impact on the firm, such as an industry-specific tax change, new legislation, or a force majeure

(e.g., floods, hurricanes and tornadoes). See Sappington, David E. M. and Dennis L. Weisman. “Price Cap 

Regulation: What Have We Learned from 25 Years of Experience in the Telecommunications Industry?” Journal of 

Regulatory Economics 38, no. 3 (2010): 227-257. In the UK, the charges distribution companies pay for 

connections to the transmission network and property taxes are treated as z-factors. See Joskow, Paul L. “Incentive 

Regulation in Theory and Practice: Electricity Distribution and Transmission Networks,” In Economic Regulation 

and Its Reform: What Have We Learned? edited by Nancy L. Rose, 291-344. Chicago: University of Chicago Press, 

2014. The price cap formula including the z-factor can be written as: 

AAAAAAAAA pppp h y = AAAAAAAAA pppp y × (1 + CCC − (+/−) z).
19

In the price cap model, the firm has a built-in incentive to minimize costs because the focus of 

regulatory control is price, not profit; however, there is an added incentive to improve efficiency 

and reduce costs beyond the level required by the x-factor. By taking steps to make its actual 

rate of productivity improvement higher than x, management at the private partner can boost its 

profit potential. The chart below illustrates the relationship between a hypothetical firm’s 

revenue per dollar of cost and productivity performance. If the firm’s rate of productivity 

improvement just matches the hypothetical x-factor of 2 percent, revenue earned per dollar of 

cost will remain unchanged. However, if the annual rate of productivity improvement can be 

raised, revenue per dollar of cost will steadily increase, as illustrated by the 3-percent line. On 

the other hand, if actual productivity improvement is less than 2 percent because management 

fails to hold down operations and maintenance costs, revenue per dollar of cost will steadily 

decline.

In order to realize the price cap model’s potential to balance investor and consumer interests 

while encouraging cost efficiency, contract negotiations must determine an appropriate value of 

x. If the public sponsor underestimates the firm’s ability to improve its productivity, then the 

negotiated x value may be too low and a relatively large share of efficiency gains will accrue to 

the private partner. If x is set too high, then the price cap — and revenue — will be too low, 

possibly putting the project’s financial soundness at risk and compromising the private partner’s 

ability to be cost efficient.

The PPP contract should also be flexible enough to adjust to significant differences between the 

firm’s actual and expected productivity performance that, for example, might be due to 

unanticipated technological innovation. A provision calling for a periodic reevaluation of the xfactor would prevent the contractual value of x from getting too far out of alignment with actual 

performance; it would also ensure that consumers continued to receive a share of efficiency gains 

and long term price protection, while preserving the firm’s incentive to operate efficiently. For 
20

example, in the UK, the x-factor applied to British Telecom is reset by the regulator about every 

five years.55 

Maintaining acceptable standards of service quality is an important consideration in any PPP 

contract, particularly in a price cap framework where cost-cutting incentives are especially 

strong and where the firm directly benefits from higher rates of asset utilization. Since we are 

dealing with projects in which quality metrics are observable, specific standards can be written 

into the contract to preclude cost cutting efforts that might otherwise lower quality.56 In other 

situations, the private firm may have an incentive to make additional investments in quality if the 

benefit of a higher rate of asset utilization exceeds the investment cost.57 A PPP contract could

encourage quality-enhancing investments by incorporating these expenditures in the price cap 

formula as an additional factor.58 

Similar to the basic user fee model, under a pure price cap model, demand risk is entirely borne 

by the private partner. The impact of demand variability on revenue is illustrated in the graph

below.

59 If demand falls short or exceeds expectations, the firm’s total revenue will rise or fall

proportionately, as shown by the dashed black line. 

 55 Jamison, Mark A. “Regulation: Price Cap and Revenue Cap,” In Encyclopedia of Energy Engineering and 

Technology Vol. 3, edited by Barney Capehart, 1245-1251. New York: CRC Press, Taylor and Francis. 2007. 56 See Engel, Eduardo, Ronald D. Fischer, and Alexander Galetovic. “Public-Private Partnerships: When and How.” 

Working paper, Yale University (2008). 

http://www.econ.uchile.cl/uploads/publicacion/c9b9ea69d84d4c93714c2d3b2d5982a5ca0a67d7.pdf (accessed 

March 12, 2015). Examples of quality metrics include the number of potholes on a road that must be repaired per 

time period, or percent of on-time arrivals in a transit system. A system of penalties can be included in the contract 

for failing to meet minimum quality standards, such as adjusting the price cap formula to limit allowable price 

increases below the rate of inflation, or if quality shortfalls are egregious enough, having a provision that allows the 

public sponsor to terminate the contract and transfer control to another private consortium (i.e. making the market 

for the PPP project effectively contestable).

57 For example, if using a superior brand of cement (to lower the probability of potholes and road buckling) 

increases the flow of toll-paying traffic enough to more than offset the higher construction costs, then it is in the 

firm’s interests to do so. 

58 Stolleman, Neal. “Dynamic Effects of Regulation on Exchange Carrier Incentives,” In Quality and Reliability of 

Telecommunications Infrastructure, edited by William H. Lehr, 63-82. New Jersey: Lawrence Erlbaum Associates, 

1995.

59 Since total revenue = price × quantity, the slope of the dashed black line is equal to the price cap prevailing within 

a given year (before the cap is adjusted for the next year).
21

Summary

The price cap model enables the project sponsor to transfer all demand risk to the private partner, 

as in the basic user fee model, while at the same time providing protection to consumers against 

large and unanticipated price increases. The embedded consumer protections in the price cap 

model may make PPP arrangements more attractive to project sponsors and local stakeholders. 

Moreover, the price cap framework encourages the private partner to be more cost efficient than 

does the user fee model by motivating the firm to do better than the x-factor, which constrains 

the rate of price appreciation.60 Where the project sponsor sets the x-factor will determine both 

the extent of consumer price protection and the attractiveness of the project to potential partners: 

a higher x increases any private partner’s efficiency incentives, but too high an x may deter or 

exclude many potential bidders. 

3. Sharing models: A price cap model within rate of return bounds

Contracts with explicit revenue- or profit-sharing provisions can align sponsor and investor 

interests in cases where the parties’ risk preferences and return expectations are not well-served 

by the basic user fee or availability payment arrangements.

61 These sharing models have the 

potential to increase the number of PPP deals and increase the odds of the projects’ long-term 

success by reducing the likelihood of bankruptcy or avoiding costly contract renegotiations.

62 

 60 Like the basic user fee model, firms operating under a price cap framework are exposed to operations and 

maintenance cost risk.

61 With the exception of the first very simple example, the models in this section present profit-sharing, or more 

accurately, the sharing of return on investment. These models can also be applied to revenue-sharing; however, the 

risk allocation depends on whether profit or revenue is shared. The private partner is fully exposed and partially 

exposed to operations and maintenance risk under revenue-sharing and profit-sharing, respectively. 62 Various types of earnings-sharing mechanisms have been used in the regulated telecommunications, electricity 

(27 states plus DC), natural gas (13 states) and water industries (New York state only). See Sappington, David E. 
22

Sharing can be achieved when the private partner remits a contractually-defined proportion of

revenue or profits to the government; risks are shared, rather than wholly allocated to one party 

or the other. In its simplest form, the government and private party share revenue in the same 

contractually-determined proportions at all revenue levels; the graph below illustrates an 

example where the project sponsor receives 20 percent of gross revenue.63,64

A risk-sharing contract should be flexible enough to provide investors and public sponsors with a 

set of acceptable risk-return tradeoffs over a range of uncertain future demand. In particular, a

sharing contract can balance 1) the investor’s willingness to share a portion of the project’s 

upside potential in return for getting some downside risk protection, with 2) the sponsor’s 

willingness to provide a degree of downside protection in exchange for a share of the project’s 

 M. and Dennis L. Weisman. “Price Cap Regulation: What Have We Learned from 25 Years of Experience in the 

Telecommunications Industry?” Journal of Regulatory Economics 38, no. 3 (2010): 227-257; and The Brattle 

Group. “Alternative Regulation and Ratemaking Approaches for Water Companies,” September 30, 2013. 

http://www.nawc.org/uploads/documents-andpublications/documents/NAWC_Brattle_AltReg_Ratemaking_Approaches_102013.pdf (accessed March 8, 2015). 63 While not depicted in the graph, a proportional revenue-sharing model in which the government bears downside 

risk will require the public sector to share in losses by making payments to the private party.

64 Revenue-sharing arrangements can be more complex. The term sheet describing anticipated contract terms for the 

State Highway 183 Managed Lanes project to increase capacity and relieve expected congestion pressures, calls for 

revenue to be shared between the private partner and the Texas Department of Transportation according to 

applicable percentages for a given range of Toll Revenues. In the example, a 20 percent assumption is used for 

simplicity. See Texas Department of Transportation. 2012. SH 183 Managed Lanes Project – Toll Concession 

Public-Private Partnership Agreement Term Sheet, SH138 Managed Lanes Project. 

https://ftp.dot.state.tx.us/pub/txdot-info/dal/sh183_managed/rfq/terms.pdf (accessed March 12, 2015). Also see

page 7 of Overview of Public-Private Partnerships for Highway and Transit Projects: Testimony Before the 

Transportation and Infrastructure Committee Panel on Public-Private Partnerships, United States House of 

Representatives. 113th Cong. 2014. http://transportation.house.gov/uploadedfiles/2014-03-05-bass.pdf. 
23

upside gain. In a contract negotiation, both sides take positions based on their own forecasts of

demand and project performance; an effective contract will allocate risks and returns in a way 

that is acceptable to both parties.

Sharing contracts can allow for both parties to share in project upside and downside. For 

example, if the project performs better than expected — by exceeding a negotiated threshold rate 

of return — the contract may call for the partners to split that portion of the return above the 

threshold in pre-determined proportions. Similarly, if the project performs worse than expected

— the rate of return falls below a negotiated threshold — the contract may specify that each 

partner absorbs part of the shortfall. Contracts may therefore involve sharing of returns below a 

lower threshold, above an upper threshold, or as we emphasize in this section, both.

How do sharing models work?

For illustration, we discuss two types of profit-sharing models. Similar revenue-sharing 

arrangements have been used in road and transit PPPs in Europe, Latin America, and Asia.

65 

Proportional sharing of high and low returns

Sharing contracts can insulate both parties when demand deviates substantially from initial 

forecasts by allowing the private partner to retain all profits in a central range of the rate of 

 65 Variations of sharing are used in a number of countries. On Federal Trunk Roads in Germany, approximately 20 

percent of toll revenue is allocated to the toll operator for operating the electronic toll charging system, while the 

remaining 80 percent is allocated to enhancing federal transport networks. See Böger, Torsten R. “PPP Projects in 

Germany.” Presentation at Konference om OPP med fokus på transportsektoren, May 27, 2014. 

http://www.toef.dk/file.php?name=/files/OPPHorten/Torsten%20B%20VIFG.pdf (accessed March 9, 2015). 

London Underground PPP contracts specify the allowable rate of return on equity and allow for a review of outputs 

and prices every seven and one-half years, including an extraordinary review if costs become significantly out of 

line with baseline assumptions. See Stern, Jon. “The Role of the Regulatory Asset Base as an Instrument of 

Regulatory Commitment.” European Networks Law & Regulation Quarterly 2, no. 1 (2014): 15-27. and Bolt, 

Chris. “Regulating by Contract and License – The Relationship between Regulatory Form and its Effectiveness.” 

Presentation at University of Bath School of Management, Bath, UK, March 20, 2007. 

http://www.bath.ac.uk/management/cri/pubpdf/Occasional_Lectures/19_Chris_Bolt.pdf (accessed March 11, 2015). 

The concession contract for the A28 Toll Motorway in France provides for revenue-sharing between the concession 

company and public sponsor, equal to 8 percent initially and growing to 18 percent when cumulative cash flows 

reach contractually determined thresholds. See Goavec, Jean-Yves. “The A28 Toll Motorway – An Innovative 

Approach to Financing.” Presentation at European Transport Conference, Strasbourg, France, August 10, 2003. 

http://abstracts.aetransport.org/paper/index/id/1577/confid/9 (accessed March 12, 2015). Public authorities in Chile, 

Colombia and Korea have various forms of shared revenue risk according to ranges of revenue, e.g. if revenue rises 

above a threshold the concessionaire compensates the public authority (and conversely). See Vassallo, Jose M. 

“Traffic Risk Mitigation in Highway Concession Projects – The Experience of Chile.” Journal of Transport 

Economics and Policy 40, no. 3 (2006): 359-381.; Irwin, Timothy. “Public Money for Private Infrastructure –

Deciding When to Offer Guarantees, Output-Based Subsidies, and Other Fiscal Support.” Working paper, The 

World Bank (2003). http://elibrary.worldbank.org/doi/pdf/10.1596/0-8213-5556-2 (accessed March 12, 2015).; and 

Kim, Yong-Seong. “Public and Private Partnerships in Korea.” Presentation at the Third Session of the United 

Nations Economic Commission for Europe Team of Specialists on Public-Private Partnerships, Geneva, 

Switzerland, April 19, 2011. 

http://www.unece.org/fileadmin/DAM/ceci/ppt_presentations/2011/TOS_PPP3/5.3_Yong-Seong_Kim.pdf (accessed 

March 12, 2015). 
24

return, corresponding to the most likely outcomes, while permitting profit-sharing outside that

range. Consider a contract where the private partner retains all profits within the 3 to 7 percent 

range, but the government project sponsor shares 50-50 in any return shortfall below 3 percent or 

any returns in excess of 7 percent, as illustrated by, the graph below.66 The upward-sloping 

dashed black line represents the rate of return under a pure price cap model, in which the private 

sector takes on all of the demand risk; the solid blue lines represent the private sector return 

above and below the negotiated return thresholds. The private partner keeps all of the return 

between the negotiated thresholds of 3 percent and 7 percent (the “Intermediate” demand range) 

and assumes all of the demand risk. In this range, in which there is no sharing, the contract 

operates like a pure price cap model. The incentives for cost efficiency and exposure to 

operations and maintenance risk are the same as in the price cap model.67,68

In both the “Low” and “High” ranges, demand risk, incentives for cost efficiency and exposure 

to operations and maintenance risk are qualitatively the same as in the rate of return model.69 If 

 66 By return, we mean: [revenue – (operations & maintenance expenses + depreciation + taxes)] /fixed assets. In a 

rate of return model, fixed assets would essentially correspond to the rate base. 

67 Since the price cap is constant within a given year, the extra revenue produced by an increase in demand along the 

x-axis, e.g. one additional vehicle on a toll road translates into a higher rate of return on the rate base, which is 

shown on the y-axis. In this simplified example, costs are also assumed constant during the year. 68 Engel, Eduardo, Ronald D. Fischer, and Alexander Galetovic. “The Basic Public Finance of Public-Private 

Partnerships.” Journal of the European Economic Association 11, no. 1 (2013): 83-111. 69 In the Low and High ranges, the closer the blue line is to the dashed black line, the more efficiency incentives and 

risk exposures resemble the price cap model, while the closer the blue line is to the horizontal, the more incentives 

and risk exposures resemble the rate of return model with very frequent (i.e. instantaneous) price adjustments. If 

there is a demand shortfall, for instance, and a price increase is implemented to reestablish the rate of return along 

the blue line, the size of the required price increase will be smaller than otherwise, because the allowed return in the 

Low range is less than three percent. As a result, the public sector still has exposure to demand risk, but the 

magnitude of the exposure is reduced compared to the rate of return model. 
25

demand falls into the Low range, the private firm will absorb just half of the shortfall between 

the 3 percent threshold and the actual rate of return, experiencing the return illustrated by the 

solid blue line. The government will either compensate the private partner for half of the 

shortfall below 3 percent either by raising taxes, issuing public debt, or reallocating funds from 

other public uses, or it may allow the private partner to adjust prices quickly to raise the rate of 

return in future periods. The PPP contract would stipulate whether returns outside the no-sharing 

range would be addressed with payments between the project sponsor and private partner, with 

price adjustments, or a combination.

70 Similarly, if demand reaches the High range, the private 

firm will share half of the return above 7 percent with the project sponsor, such that the retained 

return increases less steeply, as illustrated by the solid blue line. The private partner will pay the 

government an amount equal to half the return above 7 percent, which the government may use 

to make public investments in other parts of its regional economy, lower taxes, or retire debt. 

The contract may also call for the price to be adjusted going forward. 

Minimum profit guarantees and maximum profit cap

PPP contracts can also be structured to provide complete downside protection to the private 

partner in exchange for a limit on the upside. Consider a contract that provides the private 

partner a minimum guaranteed return of 3 percent and a maximum return cap of 7 percent, as 

illustrated by the graph below. The upward-sloping dashed black line again represents a pure 

price cap model in which the private partner bears all of the demand risk; the solid red lines 

represent the private partner’s minimum and maximum allowable returns at the negotiated return 

thresholds.

 70 A PPP contract could use payments to adjust for the past shortfall and price increases to prevent future shortfalls; 

alternatively, it could call for price adjustments large enough to compensate for the past return shortfall and prevent 

future shortfalls.
26

As in the previous example, the private partner keeps all of the return between the negotiated 

thresholds of 3 percent and 7 percent (the Intermediate demand range) and assumes all of the 

demand risk. In the no-sharing range, the contract operates like a pure price cap model without 

any sharing, and incentives for cost efficiency and exposure to operations and maintenance risk 

are the same as in the price cap model. However, in both the Low and High demand ranges, 

demand risk, incentives for cost efficiency, and exposure to operations and maintenance risk also 

match the rate of return model. 

Compared to the 50-50 proportional sharing model discussed above, the magnitude of the 

subsidy to the private partner or payments to the project sponsor are larger. If demand falls into 

the Low range, the private firm will avoid the entire shortfall between the 3 percent threshold 

and the actual rate of return, earning the return illustrated by the lower solid red line. To cover 

this shortfall, the government will compensate the private firm for the entire shortfall below 3 

percent by raising taxes, issuing public debt, or reallocating funds from other public uses; 

depending on the terms of the PPP contract, it may also allow the price to be increased quickly to 

prevent future shortfalls. If demand reaches the High range, the private firm will receive a 

constant return of 7 percent. The private partner will pay the government an amount equal to the

entire return above 7 percent, which the government may use to make public investments in 

other parts of its regional economy, lower taxes, or retire debt. The PPP contract may also call 

for price reductions to bring future returns into the 3 to 7 percent range.

Which contractual form is most attractive to investors and project sponsors will depend on risk 

appetites and return expectations. Relatively risk-averse investors or investors with low 

confidence in the demand forecasts may be willing to accept a maximum return cap in exchange 

for being fully protected if returns are much lower than expected. Investors who are willing to 

assume greater risk and are more optimistic about demand may prefer the first contract because it

offers higher return potential in exchange for less protection on the downside. 

Summary

Sharing models retain the private partner’s financial incentive to increase profits while aligning 

the interests of government and investors. Moreover, for greenfield projects — where demand 

projections are most uncertain — sharing the impact of large forecast errors reduces the risk of 

contract renegotiation. Arrangements that include sharing when returns fall below contracted 

rate of return thresholds would partially insulate the private firm from the demand shortfall,

reducing the risk that the project company enters bankruptcy or seeks to renegotiate to avert 

bankruptcy.

Sharing models can also protect the project sponsor and local stakeholders against 

underestimation of demand or large rate increases by the private partner. If demand is much 

higher than expected, the government will receive revenue that it can deploy to make other 

investments, lower taxes, or retire debt. The benefit of the shared revenue to the government and

its constituents should reduce the government’s incentive to renegotiate. Similarly, the sharing 

of returns above an upper threshold will dampen the private partner’s incentive to raise prices to 

a level that would drive returns above the threshold.
27

IV. Conclusion

Realizing the potential benefits of PPPs for taxpayers — including lower costs, better service 

quality and faster project delivery — depends on allocating project risks to the party best able to 

manage them. Arguably, demand risk is the most important source of uncertainty affecting the

financial viability of an infrastructure project in which user volume determines the private 

partner’s compensation, particularly in the case of new build, or “greenfield” projects, for which 

no history of use exists. 

We introduce three incentive structures for PPP contracts that may benefit both public sector 

sponsors, by creating value for taxpayers, and private investors, by generating attractive returns. 

Applying principles from the regulation of privately-owned energy and telecom infrastructure to 

PPP projects in which the private partner assumes temporary control of the infrastructure, the 

proposed approaches are designed to broaden the scope for PPP negotiations that voluntarily 

incorporate some of these features into PPP contracts. This process can help to create options 

attractive to investors and sponsors with risk preferences and return expectations not 

accommodated by more commonly used models. By aligning investor and sponsor interests, 

these incentive structures have the potential to increase the number of PPP deals and increase the 

odds of the projects’ long-term success.