NATIONAL MOTORISTS ASSOCIATION
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Massachusetts Page |
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Yellow Duration Engineering Standards
Yellow intervals can be correctly timed with the Institute of Transportation Engineers (ITE) formulas based on the actual 85th percentile speeds of traffic plus the physical characteristics of the pavement, grade slope, width of the intersections and other technical factors. (This reasoning is based on actual stopping times of modern vehicles. For instance, Car and Driver magazine measured a 7,000-pound GMC pickup truck traveling at 35 mph needing 3.7 seconds to come to a complete stop.)
An easy check for a normal intersection is to measure the yellow intervals based on these criteria:
- The minimum yellow-light time shall be three seconds for intersection signals on streets with actual 85th percentile approach speeds of 25 mph, or less. (The 85th percentile speed is the speed at or below which 85 percent of free-flowing traffic is traveling. This speed is often above the official speed limit)
- The yellow-light interval shall be increased half a second for each 5-mph increase in the 85th percentile approach speeds (not the speed limit) above 25 mph.
THEREFORE THE PROPER TIMING SHALL BE AS FOLLOWS
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| 85 Percentile Approach Speed | | | Duration of Yellow |
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| 25 mph | | | 3 sec |
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| 30 mph | | | 3.5 sec |
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| 35 mph | | | 4 sec |
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| 40 mph | | | 4.5 sec |
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| 45 mph | | | 5 sec |
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| 50 mph | | | 5.5 sec |
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