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D6359-99 – Standard Test Method Technical Guide
📐 Scope and Key Terminology
The ASTM D6359‑99 standard defines the minimum retroreflective properties for newly applied horizontal pavement markings (e.g., traffic stripes and symbols) that incorporate retroreflecting spheres. It is intended to ensure adequate nighttime conspicuity for drivers when measured with portable hand‑operated instruments. A marking is considered “newly applied” if it has been installed within 14 days prior to testing and all excess glass spheres have been removed. Key terms include:
- Coefficient of retroreflected luminance (RL) – expressed in candelas per square metre per lux (cd·m⁻²·lx⁻¹) or commonly in millicandelas per square metre per lux (mcd·m⁻²·lx⁻¹).
- Acceptable quality level (AQL) – the maximum percent defective that can be considered satisfactory for sampling inspection.
- CEN geometry – the measurement geometry specified by CEN, simulating a passenger vehicle with defined eye and headlight heights.
⚙️ Test Geometry and Preparation
Measurements must be performed using portable retroreflectometers that conform to Test Method E 1710 and the CEN geometry. The geometry is based on a viewing distance of 30 m from a vehicle with an eye height of 1.2 m and a headlight mounting height of 0.65 m, both in the same vertical plane. The following table summarizes the key geometric parameters:
| 📏 Parameter | 🎯 Value |
|---|---|
| Viewing distance | 30 m |
| Eye height | 1.2 m |
| Headlight mounting height | 0.65 m |
| Instrument geometry | Same as CEN/EN 1436 |
💡 Tip: Excess glass spheres (i.e., those not properly embedded) can cause erroneously high readings immediately after application. They should be removed by strong brushing, air pressure, or other methods that do not disturb correctly embedded spheres. This step is critical for accurate RL measurement as per Section 1.3.
📊 Compliance and Sampling
The specification applies to markings evaluated within a “global control area” (e.g., road segments containing lines, symbols, legends). A “checkpoint area” is defined as the marking area to be assessed within each measurement zone. The acceptable quality level (AQL) represents the maximum proportion of readings below the minimum RL threshold that is considered acceptable. The table below outlines the essential compliance conditions:
| 📋 Condition | ⚡ Requirement |
|---|---|
| Newly applied markings | Test within 14 days of application |
| Glass spheres | Remove all excess spheres before testing |
| Measurement geometry | Must follow CEN geometry (per E 1710) |
| Sampling standard | Refer to Mil‑Std 105D for inspection by attributes |
⚠️ Important: The AQL is not a fixed value in this standard; it is determined by the user based on the sampling plan (e.g., from Mil‑Std 105D). The “percent defective” refers to the proportion of RL readings that fall below the minimum acceptability threshold.
❓ Frequently Asked Questions
🔍 What is considered a “newly applied” pavement marking under D6359‑99?
Newly applied markings are those that have been installed within 14 days before testing and from which all excess glass spheres have been removed. This ensures that the measurement reflects the marking’s true retroreflective performance without the temporary influence of loose spheres.
💡 What is the CEN geometry and why is it used?
The CEN geometry replicates the view from a passenger vehicle at 30 m, with an eye height of 1.2 m and a headlight height of 0.65 m. This geometry is prescribed by Test Method E 1710 and aligns with European standard EN 1436, providing a realistic simulation of nighttime driving conditions.
⚡ How is the coefficient of retroreflected luminance (RL) measured?
RL is measured using a portable retroreflectometer that follows the CEN geometry. It is the ratio of the luminance of the marking to the normal illuminance, expressed in cd·m⁻²·lx⁻¹ (or mcd·m⁻²·lx⁻¹). The instrument projects light at the defined angle and measures the reflected light from the marking.
📌 What is the acceptable quality level (AQL) in this standard?
AQL is the maximum percent defective (i.e., readings below the minimum RL) that is considered acceptable for the process average. It is not specified numerically in D6359‑99; instead, users must define their AQL based on a recognized sampling plan, such as those in Mil‑Std 105D, and apply it to the global control area.