Shape and color play an important role in highway signs. It is practically impossible to read every sign, but you can use their color and shapes to pick out those that are most important to you. Even if you cannot read them, from a distance, their shape and color give you some idea of their meaning.

For example, both the shape and color of this sign tell you to STOP.

As a rule the color red indicates stop or conveys a significant prohibition.

Black and white signs are regulatory and state the law. They mark where the regulation goes into effect.

For example, accelerating when you first see this regulatory sign violates the law.

Wait until you have passed the sign to accelerate.

Violating any regulatory or prohibition sign can get you into serious trouble.

Yellow signs provide warnings. They alert you to curves, crossings, speed limit changes, slippery roads, and other conditions where a little warning goes a long way.

Yellow signs may also appear before regulatory or prohibition signs warning you of a change in the law or a need to take action. Look for triangles or diamonds to anticipate what is ahead.

An orange sign indicates a construction zone. A symbol usually found on a sign of another color or shape can often be found on an orange sign.

This conveys the same information but with the additional warning to be extra careful in the construction zone. Begin to slow down to the reduced speed limit before you enter the zone. Follow the directions of lane change arrows, shoulder work ahead signs, changeable message signs and be alert for shoulder drop-offs and bump signs.

There is more than one good reason to slow down at construction zones. Perhaps the most important reason is that each year dozens of highway and maintenance workers die as a result of traffic collisions at construction zones. When the signs say "Slow Down" – slow down. In addition, watch out for construction workers near the roadway. Be cautious, and obey posted signs; conditions change rapidly in construction zones.

Green signs tell you the distance or direction to cities, alternate routes, or other destination information.

In the US, distances are shown in miles. In Canada and Mexico, on the other hand distances and speed limits are measured in kilometers.  If you are not familiar with metric conversion:

	100 miles = 160 kilometers and,
	55 mph is approximately equal to 90 km/h

Blue signs provide service-related information, such as where to find food, lodgings, or gas.

Brown signs tell you about a recreational facility, such as a park campground, fishing site, or boat launch.

Slowing down to the advisory speed before entering the curve ensures that you will navigate the curve smoothly and safely. A 90-degree arrow means that the upcoming turn is sharp. The safe speed through the curve is 30 mph or less.

A curved arrow indicates a more shallow turn; however, you still may need to reduce your speed depending on weather conditions. Chevron alignment signs guide you through curves where the curve may be obscured. Follow the series of arrow signs (called "chevrons") to stay on the road.

Yield signs, at entrance or exit ramps, tell you to adjust your speed and look for a safe merging opportunity. Traffic on the highway, as well as exiting vehicles have the right-of-way. Unless absolutely necessary, avoid stopping on the ramp.

Restricted access "High Occupancy Vehicle" lanes are marked with black & white regulatory signs containing a white diamond. There will usually be a white diamond painted on the roadway as well.

This sign:

indicates a restricted lane for specially designated "High Occupancy Vehicles" (HOV).

Only vehicles with the required number of occupants may travel in HOV lanes. Signs will indicate the minimum number of occupants as well as the time the restrictions are in effect.

	In California, the HOV requirement is to have either 2 or 3 persons in the vehicle, depending on what the sign says.
	In Southern California, most HOV lanes are in effect 24 hours a day, while in Northern California they typically operate only during certain times.

Do not enter a restricted access lane unless you qualify to be there. If you need to make a turn across such a lane in city traffic, enter at the last possible moment, a half block or less from the turn.

Shared turning lanes, or left turn only lanes, allow you to make turns without holding up traffic behind you. Enter these lanes as close to your intended turn as possible. Never use a shared turning lane as a through lane.