NHTSA, the National Highway Traffic Safety Administration (part of the US Department of Transportation) issues many Federal Motor Vehicle Safety Standards, which are laws regulating the safety of motor vehicles in the US.
FMVSS No. 101, Controls and Displays, includes requirements for speedometers and odometers.
Speedometers
Here is an extract from FMVSS No. 101, Table 1, providing the requirements for speedometers.
Table 1
Controls, Telltales, and Indicators
with Illumination or Color Requirements
| Column 1 ITEM |
Column 2 SYMBOL |
Column 3 WORDS OR ABBRE- VIATIONS |
Column 4 FUNCTION |
Column 5 ILLUMIN- ATION |
Column 6 COLOR |
|---|---|---|---|---|---|
| Speedometer | — | MPH, or MPH and km/h 11
|
Indicator | Yes | — |
11. If the speedometer is graduated in miles per hour and in kilometers per hour, the identification must be “MPH and km/h” in any combination of upper and lowercase letters.
Thus, speedometers must show miles per hour (as “MPH”) and may optionally show kilometers per hour.
In the most recent revision of the rule, NHTSA considered whether to require both units:
Western Ergonomics, Inc. stated that allowing speedometers to be indicated in km/h as an option, rather than as a requirement (with MPH) is a “mistake”, since many American vehicles are driven in Canada where the speed limits are designated in km/h. We note that although many American cars are driven in Canada, most of them are not. Since speed limits in the US are expressed in MPH, in this final rule we are only requiring speedometers to be indicated in MPH. However, the rule permits manufacturers, at their option, to designate speedometers in MPH and km/h. Americans who drive in Canada (and other parts of the world that use kilometers) can look for the km/h designation in the speedometers before purchasing, leasing, or renting motor vehicles.
Odometers
Here is an extract from FMVSS No. 101, Table 2, providing the requirement for odometers.
Table 2
Identifiers for
Controls, Telltales, and Indicators with
No Color or Illumination Requirements
| Column 1 ITEM |
Column 2 SYMBOL |
Column 3 WORD(S) OR ABBREVIATION |
|---|---|---|
| Odometer | — | Kilometers or km, if kilometers are shown. Otherwise, no identifier is required. |
FMVSS No. 101 text
FMVSS No. 101 is codified as 49 CFR 571.101. Here is the full text of FMVSS No. 101 (PDF, 423 kB, 18pp; to skip to the rule text, see PDF p. 12) from the Federal Register notice (70 FR 48295) containing the final rule.
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