Traffic Signals: A Comprehensive Guide
Regulatory Signals
Definition
Regulatory signals notify road users about priorities, prohibitions, restrictions, obligations, and authorizations. Violating these signals constitutes a traffic infringement.
Classification
Regulatory signals are categorized based on their function:
- Priority (RPI)
- Prohibition (RPO)
- Restriction (RR)
- Obligation (RO)
- Authorization (RA)
Features
Form and Color
Most regulatory signals are circular, except when they include a legend, in which case they are enclosed in a box. The legend should be clear and concise. Exceptions include YIELD (RPI-1), STOP (RPI-2), and parking permission (RA-1) signs.
The background color is typically white, with red or blue used exceptionally. The border is usually red, with green or black used in specific cases. The legend, symbol, and background are generally black, white, or gray, with exceptions.
Message
In addition to symbols, a legend may be necessary to convey the message effectively, especially for prohibitions or restrictions that apply only during certain periods. In such cases, the symbol should be accompanied by a caption indicating the applicable time and/or days, preferably using a 24-hour format. For example, “21 to 6 hr” is preferred over “9:30 PM to 6:15 AM.”
Location
Regulatory signals should be placed where the regulation applies. If traffic or road conditions require, they may be repeated on the left side to ensure visibility and compliance.
Signal Priority
Priority signals regulate the right of way. In addition to traffic lights, there are three main types: YIELD (RPI-1), STOP (RPI-2), and STOP CHILDREN (RPI-3).
Justification for Installation
When the vehicle volume converging at an intersection from all branches exceeds 100 vehicles per hour in urban areas or 50 vehicles per hour in rural areas at any time of day, traffic flow should be controlled by a YIELD (RPI-1) or STOP (RPI-2) signal. The choice between the two depends on visibility at the intersection.
A YIELD (RPI-1) signal is used when drivers on the lower-priority road can easily see vehicles on the higher-priority road, allowing them sufficient time and distance to yield before entering the intersection. Otherwise, a STOP (RPI-2) signal should be used.
Hazard Warning Signs
Definition
Hazard warning signs, also known as preventive signs, alert road users to potential hazards or unexpected situations on or near the road, whether permanent or temporary.
Purpose
These signs prompt drivers to take necessary precautions, such as reducing speed or performing maneuvers, to ensure their safety and the safety of other vehicles and pedestrians. Their use should be minimized to avoid desensitizing drivers to their importance.
Classification
Hazard warning signs are categorized based on the origin of the hazard:
- Geometric characteristics of the road (PG)
- Physical constraints of the road (PF)
- Intersections with other routes (PI)
- Operating characteristics of the road (PO)
- Special situations (PE)
Features
Form and Color
Hazard warning signs are typically square with their diagonals positioned vertically. They have a yellow background with black symbols, legends, and borders.
Location
Hazard warning signs should be placed sufficiently in advance to give drivers adequate time to perceive, identify, decide, and execute the necessary maneuver safely. This time can range from three seconds for simple warnings (e.g., CURVE TO THE RIGHT (PG-1a) or STEEP DESCENT (PG-7a)) to 10 seconds for complex situations (e.g., intersections and forks (PI-4a to PI-4f)).
The distance between the sign and the hazard is determined by the maximum speed limit and the required reaction time (distance = time x speed), with a minimum distance of 50 meters. This distance can be adjusted by up to 20% based on factors such as road geometry, access, visibility, and traffic volume.
Warning signs for road restrictions that affect only certain vehicles should be placed before the junction with the alternative route that avoids the restriction or before a point where the affected vehicle can make a U-turn. The alternate route should have informational signs to guide drivers back to the original route.
When the distance between the warning sign and the hazard exceeds 300 meters, an additional panel indicating the distance should be added to the sign. If the distance is less than one kilometer, it is indicated in multiples of 100 meters; if greater, it is rounded to the nearest kilometer.
Information Signs
Definition
Information signs guide road users by providing necessary information to help them reach their destinations safely, easily, and directly.
Purpose
Information signs provide details about:
- Links or connections with other routes
- Suitable routes for each destination
- Directions to places, streets, or roads
- Exit points to other routes
- Distances to destinations
- Road and street names
- Services and tourist attractions near the road
- Names of cities, rivers, bridges, streets, parks, historical sites, etc.
Classification
Information signs are classified based on their function:
a) Signals that guide users to their destination:
- Pre-signing (IP)
- Direction (ID)
- Confirmation (CI)
- Road identification (IV)
- Location (IL)
b) Signals with other information of interest:
- Service (IS)
- Tourist attraction (IT)
- Other signs for highways and expressways (IAA)
- Other (IO)
Features
Form and Color
Information signs are generally rectangular, with exceptions like arrow signs and road identification signs (e.g., PAN-AMERICAN HIGHWAY SHIELD (IV-1) and ROAD NUMBERING SHIELD (IV-2)).
Legends, symbols, and borders are typically white. Signs for highways and expressways have a blue background, while those for conventional routes have a green background. Exceptions include street name signs (IV-3) and tourist attraction signs, which have black and brown backgrounds, respectively.
Message
Information is conveyed through a sequence of signs designed and positioned to work together. Depending on the road’s characteristics and hierarchy, some or all of the listed sign types may be used to guide users to their destinations.
Legend
To minimize driver distraction, an information sign’s text should not exceed three lines.
Arrows
Arrows are used to associate routes with destinations and indicate the direction to take at exits. In the first case, each arrow on overhead signs should point directly to the center of the associated route. In the second case, the arrow should be horizontal or obliquely ascending, accurately representing the exit angle.
Size and Layout
In these signs, the legends are written in CAPS when the minimum height required for
points is less than or equal to 15 cm. If higher, may be used sensitive and must begin each word with a
capital whose height should be 30% higher than the sensitive.
Location
The longitudinal location information signal is determined by their function and specified below
for each type of signal. However, this location can be adjusted up to 20% depending on the
site conditions and factors such as track geometry, accessibility, visibility, traffic, composition of this
and
Preseñalización signals (IP)
These signals provide information on the proximity of a link or connection with other pathways, indicating the distance to these, the
name or code of the major routes and destinations they can reach. With this information
Drivers can start the selection or tracks that allow you to leave the path or continue in it. In
Figure 5-6 shows examples of these signals.