Traffic Signal Classification and Guidelines
Signal Classification
Traffic signals are classified into three main categories:
1. Regulatory Signs
These signs notify road users of priorities, prohibitions, restrictions, obligations, and authorizations. Violating these signs constitutes a traffic infringement.
- Examples: Yield signs, Stop signs, Parking permitted signs
2. Hazard Warning Signs
These signs warn users of potential hazards or unexpected situations on or near the road, either permanently or temporarily. They are also known as warning signs.
- Examples: Curve ahead signs, Steep slope signs, Intersection signs
3. Informative Signs
These signs guide users and provide necessary information to reach their destinations safely and efficiently. They also provide information about distances, routes, street names, points of interest, and services.
- Examples: Destination signs, Direction signs, Service signs, Tourist attraction signs
Core Features of Traffic Signals
Message
Each signal must convey a clear message using symbols and/or legends (words and/or numbers). Symbols are generally understood more quickly than legends, so they are preferred. Symbols should correspond to those specified in the relevant traffic manual.
Form and Color
The shape and color of each signal are crucial for recognition and understanding. Generally, vertical signals have the following characteristics:
- Regulatory Signs: Circular shape, primarily white, red, and black, with exceptions in blue, green, and gray.
- Hazard Warning Signs: Yellow square with one diagonal vertical, black symbol and legend.
- Informative Signs: Rectangular shape, blue or green background (exceptions for tourist signs and street name signs).
Size
Signal size depends on the maximum speed limit, ensuring visibility and readability from a safe distance. Minimum dimensions are defined for different speed ranges.
Retroreflectivity
Signals must be visible at all times, including at night. They are made of materials and undergo procedures to ensure retroreflectivity, which enhances visibility when illuminated by vehicle headlights.
Factors to Consider for Signal Location and Efficiency
Longitudinal Location
Signals should be placed to allow drivers sufficient time to react and maneuver appropriately based on the message. This may involve indicating the start and end of a restriction or warning about upcoming road conditions.
Lateral Location
Signals should be placed within the driver’s cone of vision, typically within 10° from the visual axis, and at an appropriate distance from the road, neither too high nor too low.
Height
Signal height should ensure visibility, considering factors like vehicle height, vegetation, and obstacles. Road geometry should also be taken into account.
Orientation
Signals should be oriented to minimize specular reflection, which can impair visibility. An optimal angle between the signal face and the road axis is recommended.
1. Regulatory Signs
Classification
- Priority (RPI)
- Ban (RPO)
- Restriction (RR)
- Obligation (RO)
- Authorization (RA)
Features
Form and Color
Most regulatory signs are circular, with exceptions for signs with supplementary legends. They are primarily white, red, and black.
Message
Symbols are often sufficient, but legends may be necessary to specify time-limited prohibitions or restrictions. Clear and concise legends are essential.
Location
Regulatory signs are placed where the regulation applies and may be repeated on the left side for better visibility and compliance.
2. Hazard Warning Signs
Classification
- Warning of geometric characteristics of the track (PG)
- Warning about physical constraints of the track (PF)
- Warning of intersections with other routes (PI)
- Warning about operating characteristics of the track (PO)
- Warning on special situations (PE)
Features
Form and Color
Generally, hazard warning signs are yellow squares with black symbols, legends, and borders.
Location
Warning signs are placed in advance to give drivers adequate time to perceive, identify, decide, and execute safe maneuvers. The required time varies depending on the complexity of the situation.
3. Informative Signs
Classification
a) Signals that guide the user to their destination:
- Preseñalización (IP)
- Direction (ID)
- Confirmation (IC)
- Identification vial (IV)
- Location (IL)
b) Signals with other information of interest:
- Service (IS)
- Tourist attraction (IT)
- Other signs for freeways and expressways (IAA)
- Other (IO)
Features
Form and Color
Informative signs are typically rectangular, with exceptions for arrow signs and route identification signs. They generally have white legends, symbols, and borders on a blue (motorways) or green (conventional routes) background. Tourist attraction signs have a brown background, and street name signs have a black background.
Message
Informative signs often work in sequences to guide users to their destinations. The specific signs used depend on road characteristics and hierarchy.
Legend
To minimize driver distraction, informative signs should not contain more than three lines of text.
Arrows
Arrows are used to associate lanes with destinations and indicate directions at exits. They should clearly point to the relevant lane or represent the angle of departure.
Size and Layout
Legends are written in capital letters when the minimum required height for letters is less than or equal to 15 cm. For larger signs, sentence case may be used, with the first letter of each word capitalized and 30% larger than the other letters.