200mm vs 300mm vs 400mm Traffic Lights: Size Selection by Road Type

Traffic signal diameter is not a cosmetic choice. The size of the light directly determines how far away a driver can read it—and choosing a signal that is too small for the road speed or viewing distance is a safety problem, not a budget saving. Most projects use one of three standard diameters: 200 mm (8 inch), 300 mm (12 inch) or 400 mm (16 inch).

This guide explains how signal size relates to road type and viewing distance so you can select the right diameter for your project.

Why signal size is a safety specification

A driver approaching an intersection must recognize the signal, read its color and react in time. The faster the traffic and the longer the viewing distance, the larger the signal face needs to be to remain legible. National and international standards therefore tie signal diameter to road speed, approach distance and intersection type. Selecting the correct size is part of compliance, not just engineering preference.

The three standard diameters

200 mm (8 inch)

The 200 mm signal is the compact standard, widely used for lower-speed urban roads, pedestrian crossings, bicycle signals, side streets and locations where the viewing distance is short. Its smaller face suits lower approach speeds and tighter mounting spaces, and it is the most economical option. Many parking, toll and industrial applications also use 200 mm signals.

300 mm (12 inch)

The 300 mm signal is the most common full-size standard for general intersections. It offers a longer viewing distance and higher visibility than 200 mm and is the default choice for typical urban and suburban arterial roads in many countries. Where a single diameter must serve most intersections in a network, 300 mm is the usual standard.

400 mm (16 inch)

The 400 mm signal is used where maximum visibility is required: high-speed roads, wide multi-lane intersections, long approach distances or locations with complex backgrounds. Its large face ensures the signal can be read early enough for high-speed traffic to react safely.

How to choose the right size

Start with the requirements of your local standard, which will specify the required diameter for each road type and speed. Then consider the practical factors:

• Road speed — higher speed demands a larger, earlier-readable signal.
• Viewing distance — long approaches and wide junctions favor 300–400 mm.
• User type — pedestrian and bicycle signals are commonly 200 mm.
• Mounting constraints — space, wind loading and pole capacity can limit size.
• Background and lighting — cluttered or bright backgrounds may need a larger face.

Size and LED optics work together

Diameter alone does not guarantee visibility—the LED module and lens determine how the light is distributed. A well-designed 300 mm signal with correct intensity and viewing angle can outperform a poorly designed larger unit. When specifying size, confirm the luminous intensity class and standard the signal meets, not just the diameter.

Traffic light size FAQ

What is the difference between 200mm and 300mm traffic lights?

The 200 mm signal is smaller and used for lower-speed roads, pedestrian and bicycle signals and short viewing distances. The 300 mm is the standard full-size signal for general intersections, offering greater visibility and a longer viewing distance.

Which size should I use for a highway?

High-speed roads and long approach distances typically require 300 mm or 400 mm signals so drivers can read the indication early enough. Always follow the diameter specified by your national standard for the road's speed class.

Are 200mm signals suitable for pedestrian crossings?

Yes. Pedestrian and bicycle signals are commonly 200 mm because the viewing distance is short and the user is close to the signal. Many projects use 200 mm specifically for pedestrian aspects alongside larger vehicle signals.

Does a larger signal always cost more?

Generally yes—a larger diameter uses more LEDs and housing material. However, the correct size is a safety and compliance requirement, so cost should be weighed against the viewing-distance needs of the road, not chosen on price alone.

GAOQIAO manufactures 200 mm and 300 mm LED traffic lights in multiple aspect and color configurations, with OEM/ODM service for national standards. Browse the traffic light range, or send your project specification for the right size and configuration.