According to the Manual on Uniform Traffic Control Devices, a sign must meet five requirements. They must fulfill a need, command attention, convey a simple meaning, command respect from travelers, and give adequate time for proper response.
The octagon is a regulatory caution because it informs motorists to do, or not do, something. This shape is exclusively used for stop signs.
The stop sign is reflective to show the same shape and color during both the day and night. Stop signs have a red background with white letters and border.
The diamond is a warning signal; alerting drivers to potentially hazardous street conditions ahead. These warning signals can alert motorists to a sharp curve ahead, caution motorists the road is slippery when wet or alert drivers of a hidden intersection.
Warning signals have a yellow background with black letters and border. The circle is a regulatory caution to inform drivers they should not be doing something.
This is a red circle outline with a slash through the middle, across a black symbol of the prohibited action. These inform motorists not to enter, perform a U-turn or turn left or right.
The pentagon is another type of warning, specifically alerting drivers to watch for schoolchildren or pedestrians nearby. These are a fluorescent yellow-green for easier visibility in low light and foggy and rainy weather.
The triangle is a different type of regulatory caution that alerts motorists to slow down because another direction of traffic has the right of way. This shape is reserved exclusively for the yield board.
The yield signal has a white background with a wide red border and letters.
The pennant is a warning that informs motorists not to pass traffic in front of them.
This is placed at the beginning of, and at intervals, along a zone where sight distance is restricted or where other conditions make passing traffic dangerous. There are two different shapes of rectangle boards: vertical and horizontal.
Vertical boards are regulatory signs, informing drivers of speed limits, weight limits and railroad. Traffic signals carry a uniform meaning across the country.
The shape and color of the board communicates the type of warning, and in some cases communicates the meaning without having to use words on the sign. Stop signs are always octagons and red in color so that even if the motorist cannot see what the letters spell; they will recognize it as a stop signal.
A railroad crossing caution signifies the intersection of a rail line and the street and can be gated or un-gated. A railroad crossing signal always uses a white X outlined in black.
Yield cautions signify the intersection of two roads where the other street has the right of way. Yield signs are always red equilateral triangles with the point down.
A railroad advance warning board alerts drivers that they're approaching a railroad crossing and is always denoted with a yellow circle. Speed limit signs denote the maximum speed you can drive on a road.
They are always white rectangles with the vertical side longer than the horizontal side. A yellow pennant denotes a no passing zone, which is common on two-line highways.
You are not allowed to go into the opposite direction of traffic's lane to pass a car ahead of you. Traffic signs and signals are used mainly to control the flow of traffic, warn motorists of dangerous or unexpected conditions or advise drivers about services available off roads and highways.
Signs and lights have specific uses for different shapes and colors. Warning boards tell drivers of upcoming conditions like steep inclines, stop signs that may not be visible from a distance or sharp curves.
Warning boards can also provide a suggested speed for dangerous conditions. Temporary boards warn motorists about detours or road construction over a short period of time.
These boards are typically orange in color. There are also specific colors used for different purposes.
Yellow is used for all warning boards, blue is used to advise drivers of upcoming gas stations or other services and white is usually used in regulatory boards. Most people are familiar with stop lights, but traffic lights can also be used to warn of fire stations or extreme conditions, regulate lane direction and traffic or control the flow of bicycles.