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Warning Lights and Warning
Messages for Nighttime
Maintenance Work Zones: How to
Get Them “Just Right”
Gerald Ullman, Ph.D., P.E.
Senior Research Engineer
Texas Transportation Institute
Nighttime Maintenance Work Activities

The good…
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◦
◦
◦

Lower traffic volumes
Less congestion and delay
Reduced driver rage
Cooler temperatures
The bad…
◦
◦
◦
◦
Higher speeds
Increased levels of impaired driving
Worker fatigue
Higher intrusion risk?
Goals When Working at Night

Gain motorist attention

Provide sufficient and positive
guidance information (minimize
confusion)

Flashing vehicle warning lights
and temporary traffic control
devices need to do both
Key Considerations of Vehicle
Warning Lights

Type (halogen, strobe, LED)
◦ Flash intensity
◦ Flash structure
◦ Flash pattern
Key Considerations of Vehicle
Warning Lights

Type (halogen, strobe, LED)
◦ Flash intensity
◦ Flash structure
◦ Flash pattern
I
T
Key Considerations of Vehicle
Warning Lights

Type (halogen, strobe, LED)
◦ Flash intensity
◦ Flash structure
◦ Flash pattern
I
T
Key Considerations of Vehicle
Warning Lights

Type (halogen, strobe, LED)
◦ Flash intensity
◦ Flash structure
◦ Flash pattern
I
T
Key Considerations of Vehicle
Warning Lights

Type (halogen, strobe, LED)
◦ Flash intensity
◦ Flash structure
◦ Flash pattern

Color
Key Considerations of Vehicle
Warning Lights

Type (halogen, strobe, LED)
◦ Flash intensity
◦ Flash structure
◦ Flash pattern

Color
Key Considerations of Vehicle
Warning Lights

Type (halogen, strobe, LED)
◦ Flash intensity
◦ Flash structure
◦ Flash pattern
Color
 Location on vehicle

Key Considerations of Vehicle
Warning Lights

Type (halogen, strobe, LED)
◦ Flash intensity
◦ Flash structure
◦ Flash pattern
Color
 Location on vehicle
 Number in overall visual field

Consequences of Excessive Vehicle
Warning Lights
Glare
 Masking effects

Consequences of Excessive Vehicle
Warning Lights
Glare
 Masking effects
 “Moth” effects

Consequences of Excessive Vehicle
Warning Lights
Glare
 Masking effects

Consequences of Excessive Vehicle
Warning Lights
Glare
 Masking effects
 “Moth” effects

Consequences of Excessive Vehicle
Warning Lights
Glare
 Masking effects
 “Moth” effects
 Photosensitive epilepsy concerns

◦ Critical range: 5-10 Hz
◦ Effects of multiple flashing light sources
unknown
Current Recommendations
(NCHRP 624)
Outline the vehicle
 Total luminance output of all visible lights
limited to 2200 cd at night
 Flashing lights preferred over steady lights
 Slower flashes preferable
 Consider the entire convoy

Warning Messages on TruckMounted Changeable Message Signs

TMCMS use increasing
for mobile and short
duration operation
◦ Good detection
◦ Message flexibility

Smaller size makes
message design more
challenging
Mobile Operation Concerns
Speed Differential
 Passing
 Wet Paint
 Workers Out of Vehicles
 Visibility

Basic Message Design Principles
No more than 4 units of information
 Each unit of information should be
readable for two seconds
 No more than two phases
 Each phase should stand alone

Acceptable TMCMS Phrases
[#] PAINT TRUCKS
 [#] WORK TRUCKS
 SWEEPING AHEAD
 YELLOW [WHITE] LINE WET
 CNTRLINE WET
 DO NOT CUT IN
 WATCH FOR WORKERS
 REDUCED VISION
 STAY IN LFT [RGT] LANE

Questions?
Gerald Ullman
Texas- Transportation Institute
(979) 845-9908
3135 TAMU
College Station, TX 77843-3135
g-ullman@tamu.edu