Warning signs in Texas must be diamond shaped with black text or border and a yellow background. Signs are placed on the road based on a formula called the Perception Response Time, which is the sum of the time it takes to detect the sign, recognize the warning and decide how to react. Signs should be placed close enough to the hazard to give drivers enough time to react but not so much time that they forget the warning.
Yellow warning signs are also placed in areas where there is a hill with a five to nine percent grade and that spans a distance of 500 to 3,000 feet. Sometimes extra signs are placed in connection with HILL signs to indicate different characteristics that drivers need to be aware of. There are also signs placed to indicate curves where large trucks or vehicles with a high center of gravity tend to rollover.
Some yellow signs indicate hazardous road conditions. A sign that reads "Slow Down on Wet Road" indicates the road may become slippery when wet. Other signs warn of possible ice on bridges, rough roads, loose sand and other problems with the road surface that may affect driving. Some signs indicate a reduced speed is necessary in order to safely navigate a stretch of road. These types of signs are usually used on freeway exits or curves where the driver may lose control if they are driving too fast.
Some signs are used to alert drivers to upcoming traffic signals when they may be hard to see from a distance or if there is something that might obscure the upcoming traffic signal. These signs might read "Stop Ahead," "Yield Ahead" or "Signal Ahead." These signs may also be used to simply put more emphasis on a traffic signal that is not obstructed.
