ISO 16121-2:2011

Overview

ISO 16121-2:2011 - "Road vehicles - Ergonomic requirements for the driver's workplace in line-service buses - Part 2: Visibility" defines visibility requirements for drivers of low-floor line-service buses. The standard applies to buses designed to carry passengers (more than eight seats besides the driver), with a maximum weight > 5 tonnes and an overall width > 2.30 m. ISO 16121-2 focuses on the driver’s field of view to the road ahead, the entrance opposite the driver, and the interior passenger compartment to reduce blind spots and improve operational safety.

Key Topics and Requirements

• Vision points (V1 and V2): Defined as points 635 mm above the H-point with the seat in rearmost/highest (V1) and foremost/lowest (V2) positions within the required H-point adjustment range. These points are the basis for visibility checks.
• Forward blind spot: A bar equal to the vehicle width placed 300 mm in front of the foremost surface at 1 100 mm above ground must be visible (direct or indirect) from V1 and V2 for at least 95% of its length. If direct vision fails, alternative devices (e.g., mirrors or video systems) must be provided.
• Lateral visibility: Where a service door is at the front corner, a 100 × 100 × 100 mm cube positioned at 800 mm above ground must be visible (at least three-fourths of one face) from V1 and V2. Adjustable dashboards are checked in mid-position.
• View upwards: To ensure visibility of traffic signals, there must be an unobstructed view through the windscreen measured through a horizontal plane intersecting V1 with a 15° inclined plane.
• Passenger compartment observation: Mirrors or other devices shall allow monitoring of gangways and entrance/exit zones not in the driver’s direct line of sight.
• Reflections: Interior and exterior reflections that impede the driver's view or interfere with information devices must be minimized.

Applications and Who Uses It

ISO 16121-2 is used by:

• Bus and coach manufacturers (design and verification of driver’s cockpit and glazing)
• Automotive ergonomic engineers (human-centred cab layout)
• Transit authorities and fleet specifiers (procurement and safety requirements)
• Regulatory bodies and compliance auditors (type approval and conformity checks)
• Suppliers of mirrors, camera/video systems and visibility aids

Practical applications include design validation, visibility testing during prototype and production stages, selection of supplementary viewing systems, and improving driver situational awareness to reduce accidents and boarding incidents.

Related Standards

• ISO 16121-1: General description and basic requirements (normative reference)
• ISO 16121-3: Information devices and controls
• ISO 16121-4: Cabin environment

Note: Where national legislation exists, that legislation takes precedence for conflicting points.