oad markings appear bright at night when glass beads return vehicle-headlight illumination toward the driver. When markings lose reflectivity, the cause may be bead loss, incorrect embedment, surface wear, moisture, contamination or poor application control.

FHWA notes that maintained retroreflective pavement markings improve nighttime visibility by returning light toward the vehicle and driver. Diagnosing reflection problems therefore requires examining the complete marking system rather than only the paint.

How Retroreflection Works

Light enters the exposed portion of a glass bead, bends inside it, reflects near the back of the bead and returns toward the light source. Effective performance depends on bead roundness, refractive index, clarity, embedment and the contrast of the marking material beneath it.

The Most Common Causes of Reflectivity Loss

Insufficient Drop On Beads

If the application rate is too low, the surface does not contain enough optical elements to create uniform brightness.

Uneven Distribution

Blocked bead dispensers, incorrect gun alignment, unstable pressure or changing machine speed can create bright and dark sections along the same line.

Shallow Embedment

Beads that remain too high on the surface may initially look bright but are easily removed by traffic. Caltrans specifications reference uniform distribution and embedment to approximately half the bead diameter for relevant systems.

Excessive Embedment

When beads sink too deeply, insufficient bead surface remains exposed. This may occur when the thermoplastic is too hot, too fluid or receives the beads under unsuitable conditions.

Delayed Bead Application

If the thermoplastic surface begins cooling before beads arrive, they may not develop adequate retention.

Dirty or Wet Beads

Dust, moisture and damaged packaging can affect bead flow and optical performance.

Surface Wear

Traffic gradually removes the top surface. A system containing intermix beads can expose new beads as wear progresses, while a surface-only system may lose reflection more quickly.

Water Film

Water changes the path of light and can cover exposed beads. Wet-night visibility depends on bead design, marking profile, pavement texture and drainage.

Dirt Pickup

Oil, rubber, dust and road contamination can cover the bead surface and reduce brightness even when the beads remain present.

Diagnostic Table

How to Improve Reflective Performance

Treat Paint and Beads as One System

Select beads compatible with the thermoplastic binder, thickness and project standard.

Calibrate the Bead Dispenser

Verify actual output across the full line width. Do not assume the equipment setting equals the delivered dosage.

Control Material Temperature

Use the product’s recommended range. Incorrect viscosity changes embedment and retention.

Coordinate Machine Speed

Changes in speed can alter thermoplastic thickness and bead application rate per square meter.

Inspect During Application

Check the line while adjustments are still possible. Examine bead distribution visually and use the project’s approved measurement procedure.

Protect Beads in Storage

Keep bags sealed and dry. Moist beads may clump and flow unevenly through dispensing equipment.

Maintain Road Drainage

Enhanced bead systems work best when water can leave the marking surface. Standing water cannot be solved solely by increasing bead dosage.

Intermix Beads and Long Term Reflectivity

Intermix beads are distributed through the thermoplastic layer. As traffic wears the surface, new beads may become exposed. They do not eliminate the need for correct surface-applied beads, but they can support retained visibility.

The required percentage should be selected according to the project specification, product formulation and cost-performance target.