The nation’s network of roads, taken together, is the legacy of investments made over the course of many decades. The legacy includes land committed to enabling people and goods to be moved from place to place, and with that land forests and grasslands cleared, streams diverted, and flora and fauna displaced. Added to these natural resources are concrete, steel, and other materials, and the human labor of planning and construction to produce the pavement and bridges, signs and signals, guardrail and rest areas that daily carry millions of vehicles.
Despite the efforts of clever analysts, there is no authoritative appraisal of this legacy’s current value. That the legacy has any value at all is a proposition based on our society’s desire for access and mobility and our adoption of  economics as a way of understanding and directing our behavior. The protracted discussions in the U. S. Congress and many state legislatures concerning how we pay for roads and government’s role in their management is a reflection of our lack of consensus on the value of the legacy and what we should do with it in the future.
It’s as though we are beneficiaries gathered for the reading of the will following the demise of a wealthy relative. We’ve inherited a family estate and now must decide what’s to be done with the property. Is there a substantial bank account, stocks and bonds? Do any of us want to live in the mansion; can we afford it? What’s to be done with the art collection? Is the land still to be farmed or subdivided for development? Can the gardens and fen be conserved?
Our legacy is a diverse collection of assets. The fundamental questions facing us are whether to use these assets to realize the greatest return to the beneficiaries or to keep the legacy intact at the lowest cost. We may seek advice from the financial advisers, groundskeepers, curators, and other staff who have cared for these assets in the past. The answers will depend, however, on what we judge to be important, what we think we can afford to do, and how well we can agree among ourselves. It’s all very complicated.
These are the issues facing the people who take responsibility for managing our roads For more than a century the network was growing as the nation moved across the continent and trucks and cars began to compete with trains, wagons, and trams as primary means for moving from place to place. Today we have more than 4 million miles of public roads in the 50 states, District of Columbia, and Puerto Rico, according to the U. S. Department of Transportation; about 2.7 million miles of these roads are paved. The strategic core of the network is the National Highway System (NHS), about 160,000 miles of paved roads judged to be important to the nation’s economy, defense, and mobility. Within the NHS, the Interstate Highway System, inaugurated by President Eisenhower in 1956, accounts for just over one-quarter of that, about 47,000 miles. While the Interstates represent just over 1% of the nation’s road mileage, they carry about 25% of the nation’s traffic, measured by vehicle-miles of travel. (1)
We have reached a point where the demand for new roads nationwide has been largely satisfied. Additional capacity would be welcome in some places where population and jobs are growing, and this means adding lanes and upgrading standards on some routes. Substantial revisions of facilities will be wanted in other areas to enhance livability and improve safety, for example replacement of Seattle’s Alaska Way Viaduct with a tunnel. It may be that we will choose in coming years to make substantial new investments in rail transit and other forms of mass transportation, and this may necessitate alterations in communities’ roads. But in much of the nation the primary task facing the people responsible for our roads will be managing our legacy assets.
When it comes to roads and other public works, the job of “asset management†has come to mean primarily looking after the facilities’ condition and maintenance to ensure they can provide the services for which they were constructed. Other than re-purposing a freeway lane for use by high-occupancy vehicles only, dedicating road right-of-way for transit use or installation of fiber-optic cable, or converting abandoned rail lines to bicycle trails, road assets are not particularly fungible, that is, easily converted into other forms of assets. (Stock markets, for example, make it possible for owners to easily exchange shares for cash and vice versa.) The nascent market in private-sector leasing and operation of toll roads (the Chicago Skyway, for example) and other facilities are a step toward encouraging infrastructure asset managers to think about how the value of might be redeployed to increase public benefit, but we are still a long way from managing a road system as though it were a mutual fund.  In the meantime, asset preservation seems to be the primary objective, simply making sure that everything is still presentable and in working order when the family finally decides what to do.
(1) See http://www.bts.gov/publications/national_transportation_statistics/html/table_01_04.html,
http://www.fhwa.dot.gov/policy/2008cpr/es.htm