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ITIS Phrase Tables, Draft [issued: 04-11-09]
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223 -
This is a draft document of the SAE ATIS committee, subject to change.
8.6
Encoding Speed Limit Sign Patterns
Signs of this type (typically denoted by the R2 category types in MUTCD) are typically used to relate a
regulated speed to specific classes of vehicles on specific roadways or specific sections of roadway. The
most common pattern, which applies to all vehicles, is simply:
<speed><value><optional units>
However this pattern is in fact only a simple sub-set of the more complex pattern shown below which is
used in the more general case to apply the speed limit to specific conditions, user vehicles, or roadway
areas.
<pre-terms><speed><time of day modifiers><modifiers>
<class of vehicle><value><optional units><location modifiers>
The pre-terms include such phrases as “state law” or “fines doubled” etc. The speed is the critical “speed
limit” code entry (value 268 from Traffic Conditions). The time of day modifiers restricts the application of
the speed to selected time such as “night” etc. The modifiers allow the phrases like “reduced” or
“minimum” or “combined” to be inserted when needed (taken from MUTCD sign types or from qualifiers
categories). The class of vehicle allows the application of the speed to selected vehicle types or traveler
classes, such as trucks or vehicles with trailers. The value is the stated speed, and this optionally followed
by the units to be used (typically MPH or KPH). Finally the normal location modifiers can be added
(ahead, etc.) It should be noted that if such a modifier is added, the MUTCD code for the resulting sign
will be a “w” type (warning) rather than an “r” type (regulatory).
In constructing signs using these patterns the following rules shall be observed:
Any time of day restrictions shall precede any class of vehicle restrictions
Location modifiers which determine how the sign is applied to the local area shall be last
The unit’s term shall be present only when it is preceded by a numerical value.
When there is no unit code present the value shall be in units of MPH.
Examples of proper encoding of speed limit values:
Value to be expressed
Preferred Encoding
Byte Sequence
Speed Limit 70 MPH
speed limit, n70, mph
268, 12614, 8720
Night Speed Limit 55
night, speed limit, n55, mph
7743, 268, 12599, 8720
Truck Speed Limit 55
trucks, speed limit, n55, mph
9227, 268, 12599, 8720
Speed Limit 20 on curve
advice, on curve, speed limit, n20, mph
7712, 8026, 268,
12564, 8720
Speed limit Reduced Ahead
speed limit, reduced, ahead
268, 12302, 13569
Night Speed 45 Vehicle with Trailers
vehicles with trailers, night, speed limit, n55, mph
9225, 7743, 268,
12599, 8720
School Zone Speed Limit 25 MPH
school zone, n25, mph
4124, 12569, 8720
Trucks 60 km/h
speed limit, trucks, n60, kph
268, 9227, 12604, 8721