What minimum advance notice to motorists is required before a lane closure on an interstate highway, per MUTCD guidance on advance warning area length?
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A
It is uniform at 500 feet regardless of speed
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B
It varies based on posted speed limit and road type, from hundreds to thousands of feet
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C
A single 'Road Work Ahead' sign at 100 feet is sufficient
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D
Only a flag is required; distance is not specified