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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Public Roads - Sept/Oct 1998

The Metric Conversion Status for The Highway Program

by Jennifer Balis

The 1998 construction season represents a major turning point in the metric conversion process currently underway in the highway construction industry.

Data collected by the American Association of State Highway and Transportation Officials (AASHTO) indicates that just under 65 percent of the 1998 construction dollars will be let for projects using the International System of Measurements (SI). Also, current estimates by the state departments of transportation (DOT) indicate that metric units will be used in projects representing 85 percent of the entire 1999 state-administered highway construction program. These estimates are a substantial increase from 1997 when projects using metric measurements made up 45 percent of the program.

Metric conversion of the U.S. highway industry has come about primarily as a result of the 1988 Omnibus Trade and Competitiveness Act. In this act, Congress mandated that federal government agencies use the SI metric system of measurements in their daily business to encourage U.S. industry to adopt SI and to become more competitive in the worldwide market.

Although we do not export our highways, we can and do export the technology to build them efficiently. Therefore, converting the highway industry to the SI system will enable its many consultants, contractors, materials suppliers, and equipment manufacturers to compete more readily in the global marketplace.

The legislative mandate was reinforced by Executive Order 12770, signed by George Bush in July 1991, which required agencies to develop a conversion plan and timetable. The Federal Highway Administration (FHWA) Metric Conversion Plan was approved on Oct. 31, 1991. The original plan required the state DOTs to convert by Sept. 30, 1996. The National Highway System (NHS) Designation Act of 1995 revised the date to Oct. 1, 2000.

In the Transportation Equity Act for the 21st Century (TEA-21), which became law in June 1998, Congress removed the deadline entirely, making metric conversion optional for state DOTs. FHWA and AASHTO are currently reviewing the implications of this change.

The state DOTs and FHWA have been working together to coordinate an orderly transition to the SI system. As illustrated by the accompanying table and map, many state DOTs stayed with their original conversion target dates and are well along in their transition to SI. Because three years is the average time for a highway project to be developed from concept to contract, the NHS Act delay occurred too late for most states to modify their timetables without creating greater confusion.

In 1997, FHWA recognized 42 state DOTs that "substantially completed" their conversion process. "Substantial completion" means that the state DOT:

  • Has converted all (or nearly all) key tools, including standard drawings, standard specifications, and manuals, to metric.
  • Is developing all new projects in metric units.
  • Is conducting extensive outreach efforts with consultants, contractors, associations, and local agencies.

The FHWA Metric Conversion Plan does not require changing the legends on highway signs to metric units. In fact, FHWA is currently prohibited from nationally mandating sign conversion.

In carrying out the plan, the state DOTs, AASHTO, and FHWA have sought to accommodate the general public because there is no national mandate for the general public or industry to convert. Therefore, documents written for individual citizens (right-of-way documents) or available for public review (environmental documents, permit applications) are prepared in dual units unless a state DOT made the decision to use only metric units.

States reported that metric conversion has cost about $73 million over the five years from 1992 to 1997. During this same period, authorizations for the federal-aid construction program amounted to $118 billion. The average expenditure by a state DOT has been about $1.6 million, and the median cost is about $1 million. Several states did not track their conversion costs.



No major problems have been reported in metric construction projects. Bidding errors have been minimal. The learning curve for state and contract employees is short once they begin work on a metric project; the key is to work in the metric system without attempting to translate back to English inch-pound units. Designers and contractors repeatedly say that once they had worked in the metric system, they preferred its simplicity.

Small- to medium-sized contractors remain concerned about the cost of converting their operations to metric units. Currently, FHWA is funding a case study of metric highway construction projects to look at contractor conversion costs and to identify problems, solutions, and best practices.

Because highway construction methods remain the same, most of the construction problems being encountered are related to materials. These problems are not major obstacles, and they are being addressed on a case-by-case basis. As the volume of metric construction increases within each state and nationwide, these problems should diminish.

The second commonly perceived problem area is the lack of a conversion mandate beyond the federal government. Federal agencies have differed in their interpretation of the conversion requirements, resulting in an inconsistent approach to conversion by federal agencies in their operations and their requirements. Some federal agencies have issued functional equivalences for their regulations; but other agencies continue to use inch-pound units in their regulations, accepting metric units in permit applications and the like; and still others use and require inch-pound units only in their documents.

The effect on local highway agencies will vary from state to state. Some states set metric deadlines for their local agencies, but most states only encourage their local agencies to submit local projects in metric units. Many local agencies rely on the state DOT's standard plans and specifications in developing their own projects. These agencies will be forced to either use metric units, develop their own design aids, or use outdated standards when the state stops maintaining inch-pound standard plans and specifications.

Operating in a dual-unit environment is inefficient and increases the probability of error because people constantly translate between measurement systems. Therefore, several state DOTs have converted their entire organization to the metric system of measurements. This change remains largely invisible to the general public.

The continuing lack of metric awareness prompted the AASHTO Metric Task Force to develop a 30-minute "status of metrication" presentation. This presentation, which is jointly sponsored by AASHTO and FHWA, is primarily directed toward industry groups to make their membership more aware of the progress the states have made and of the fact that this progress, while not uniform, has not been piecemeal.

The future of metric conversion within the highway industry rests largely on the state DOTs. Several states indicated that they will not revert back to inch-pound measurements regardless of congressional action or further delays to the FHWA conversion deadline. Other states believe that the political climate within their state will force reversion despite the time and expense to do so. Giving the states the option to metricate creates a hodgepodge across the country; contractors, consultants, and materials suppliers operating in several states are forced to operate in a dual-unit environment. Information-sharing across state lines on highway-user statistics, interstate trucking, or major projects must be conducted in dual units. AASHTO, other industry associations, and FHWA may be forced to operate in dual units. Staying the course with metrication would be best for all in the industry. Completing the process nationwide would enable state DOTs, contractors, and materials suppliers to use a single-measurement system, reducing confusion and eliminating the need for translation or dual inventories.

For more information about the AASHTO/FHWA 30-minute "Status of Metrication" presentation, contact Dean Testa of the Kansas DOT by telephone (785) 296-3576 or fax (785) 296-6944.

Jennifer Balis is a highway engineer in FHWA's Highway Operations Division. During her time with FHWA, she has worked in the Eastern Federal Lands Highway Division, Nebraska Division, and the Office of International Programs. She has also worked for the U.S. Forest Service and the Virginia DOT. She has a bachelor's degree in civil engineering from Virginia Polytechnic Institute and State University. She is a licensed professional engineer in Nebraska.