21.4 Nighttime Driving

Headlamp intensity, ambient lighting, and glare all influence how far downstream a motorists can see and their ability to detect and respond to signs. Table 21.2 lists treatments that can reduce nighttime crashes, encourage lower speeds, and increase stop compliance at rural intersections.
Fixed road lighting does the best job of enhancing nighttime visibility. But signs, reflectors, and beacons can all improve safety by reflecting light to motorists, altering them to downstream features.

Table 21.2 Design Treatments to Mitigate Headlamp Glare
Treatment	Suggested Conditions for Use	Benefits
Safety Lighting	Dark light conditions High pedestrian traffic High average daily or nightly travel Areas with a history of crashes or a high potential for crashes	Better detection and recognition of pedestrians and vehicles Earlier speed reductions as vehicles approach intersections Most effective for crash reductions
Advance Warning Signs	Intersection approach Sharp curve approach	Earlier speed reductions as vehicles approach curves
Advance Warning Signs with Post-Mounted Beacon	Intersection approach Sharp curve approach Areas with a history of crashes or a high potential for crashes	Beacon grabs the attention of motorists and improves sign visibility Earlier speed reductions as vehicles approach marked features
Stop Sign with Post-Mounted Beacon	Intersection approach Intersections that do not merit continuous lighting Areas with a history of crashes or a high potential for crashes	Beacon grabs the attention of motorists and improves sign visibility Earlier speed reductions as vehicles approach the stop sign
Reflective Strips on Stop Sign	Unlighted or dark intersections Minor leg of a T intersection	Sign is more conspicuous because the visible surface area is larger
Raised Pavement Markers	Light conditions are dark (with or without lighting) Curves and tangents	Better lane visibility when road surfaces are wet
Intersection Flashing Beacons	Intersections where continuous lighting is not cost-effective Significant pedestrian traffic Areas with a history of crashes or a high potential for crashes	Beacon grabs the attention of motorists and alerts them to the downstream intersection Earlier speed reductions as vehicles approach the intersection

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