Design for Survival: CEN/TR 17420 and Pedestrian Safety in Urban Rail

What is CEN/TR 17420?

CEN/TR 17420 is a specialized Technical Report titled “Railway applications – Vehicle end design for trams and light rail vehicles with respect to pedestrian safety.” Unlike heavy rail standards that focus on train-to-train collisions (like EN 15227), this document addresses the specific risks of urban operations where trams share space with vulnerable road users.

In mixed traffic environments, collisions between trams and pedestrians are a significant risk. CEN/TR 17420 provides design recommendations for the shape and features of the vehicle’s front end. The primary goal is not just to soften the blow, but to manage the post-impact trajectory of the pedestrian—specifically, to prevent them from falling under the wheels (run-over) and to deflect them away from the track.

Key Design Principles

The report outlines passive safety strategies that come into play when active safety systems (like emergency braking or driver vigilance) have failed to prevent a collision.

• Shape Geometry: The front nose of the tram should be shaped to encourage the lateral deflection of a pedestrian. A rounded or wedge-shaped front is preferred over a flat, vertical surface, which tends to knock victims forward onto the track.
• Under-run Protection: Physical barriers or “lifeguards” (chasse-corps) positioned low near the rails. These devices are designed to push an object or body aside before it reaches the first wheelset.
• Surface Compliance: Recommendations on using materials or structures that can absorb some impact energy to reduce the severity of initial injuries.

Scope of Application

CEN/TR 17420 is applicable to new designs of:

Trams and Light Rail Vehicles (LRVs): Vehicles operating in city streets (Line-of-Sight operation).
It explicitly excludes heavy rail vehicles, metro systems with dedicated tracks, and special machinery, as their operational speeds and environments differ significantly.

Comparison: Active vs. Passive Safety in Trams