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Metric Conversion of the Federal-Aid Highway Program

November 4, 1998

Legislative Background:

The 1988 Omnibus Trade and Competitiveness Act (Public Law 100-418, signed into law 8/23/88), Section 5164(b) amended the 1975 Metric Conversion Act to require that Federal agencies use the International System of Measurements (SI) in their procurement, grants, and other business related activities. On July 25, 1991, President Bush signed Executive Order 12770 requiring that all Federal agencies develop timetables for their transition to the metric system.

Section 205(c) of the National Highway System Designation (NHS) Act of 1995 prohibited the Federal Highway Administration (FHWA) from mandating that the State Departments of Transportations (DOT) place metric legend signs, and which prohibited FHWA from mandating the use of metric units in the highway construction program before October 1, 2000.

However, the current statute, the 1998 Transportation Equity Act for the 21st Century (TEA-21), removes the target date for metric conversion, thus allowing the State DOTs the option of converting to SI ( see TEA-21 Section 1211(d)). Therefore, while FHWA can no longer mandate that States convert to SI, we strongly encourage its continued use.

Status of Conversion Effort:

The FHWA Metric Conversion Plan was approved on October 31, 1991. The Metric Conversion Policy was published in the June 11, 1992 Federal Register. The plan defined a five year program for complete conversion of the Federal-aid highway construction program by September 30, 1996. The FHWA's conversion timetable was set to provide ample time for FHWA, State DOTs and industry to adjust.

After the NHS Act, the American Association of State Highway and Transportation Officials (AASHTO) Metric Clearinghouse conducted a survey of the State DOTS to find out how many would maintain the timetable they had originally established for their metric conversion program. At that time, forty-five SHAs responded that they would maintain October 1, 1996, as their internal deadline; three would delay until 1997; and four (Hawaii, the Dakotas and Rhode Island) would delay until 2000.

In a follow-up Metric Clearinghouse survey, 43 SHAs responded with information about metric conversion costs. While four states (Alabama, Florida, New Jersey and Pennsylvania) had costs more than $5 million; fifteen states reported costs less than $1 million and five states had not tracked their conversion costs at all. Overall metric conversion has cost the SHAs more than $70 million with the average about $1.6 million; and the median cost about $1 million.

However, the optional conversion language in TEA-21 has resulted in a change in some State DOT conversion plans. In a post TEA-21 survey, AASHTO polled the State DOTs regarding their intentions to use SI units or revert back to inch-pound units. From the 46 responses received from the State DOTs, AASHTO found that 26 States will continue to use SI, 10 States will revert to inch-pound units and 10 were still considering the issue.

Nationwide, highway construction is about 65% in metric units for 1998; and 75% for 1999.

Highway Signing:

In 1995, the Battelle Institute conducted a study to quantify the costs of converting highway signs. This study collected information from 13 states, 67 counties, and 48 cities across the United States. Battelle determined that about six million signs which contain a dimension in their legend will need to be converted across the country. Battelle then estimated the nationwide costs using five different conversion schemes. The estimated costs range from $15 million for routine replacement of all signs to $826 million for installation dual unit sign legends.

In fiscal years 1994, 1995 and 1996, Congress prohibited the use of Federal-aid highway funds by SHAs to cover the costs of converting highway signs. There is no prohibition for fiscal year 1997.

Updated: 02/25/2015
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