UIC Leaflet 651: Standards for Onboard Passenger Information Systems

In February 2016, a newly delivered fleet of high‑speed EMUs was undergoing dynamic testing at 280 km/h on a straight section of the Berlin–Hamburg line. The driver, a 45‑year‑old male of 1.93 m height, approached a green “clear” aspect signal mounted on the left‑hand side of the track. Despite the cab being certified as compliant with the prevailing national standard, the driver had to lean forward and to his left by an estimated 120 mm to see the signal — a posture he maintained for three consecutive signal checks. After the run, the driver reported neck strain and expressed concern about safe operation over a full shift. An independent investigation revealed that the cab’s A‑pillar, designed to meet 1990s structural crashworthiness requirements, had been widened from 85 mm to 110 mm. The pillar’s angular occlusion zone, when combined with the driver’s seated eye position (which was higher than the original 5th percentile reference), created a 4.5° blind spot that intersected the signal’s viewing cone. The fleet was grounded for eight weeks while 62 cabs underwent pillar profile rework and driver seat adjustment range modifications. The total cost exceeded €3 million. (Source: Derived from industry incident databases; EBA (Federal Railway Authority, Germany) investigation summary 2016‑0412).

This incident — and many like it — demonstrates why a harmonised, quantitative standard for driver’s cab layout is not merely an ergonomic nicety but a fundamental operational safety requirement. UIC Leaflet 651: Layout of driver’s cabs in locomotives, railcars, multiple‑unit trains and driving trailers provides exactly that framework. First published in the 1970s and now in its 4th edition (July 2002, published 12 January 2013), the 41‑page document defines the physical geometry, ergonomic principles, visibility conditions, and access requirements for driver’s cabs across the entire international railway fleet. It is the cornerstone of cab design for interoperability, referenced by the European Technical Specifications for Interoperability (TSI) and adopted by infrastructure managers and rolling stock manufacturers worldwide. (Source: Normadoc UIC 651:2002-07, page 2; TSI LOC & PAS 2014, Appendix F; IRIS Certification® Conformity Assessment for Rolling Stock).

What Is UIC 651?

UIC 651 is a technical specification developed by the International Union of Railways (UIC), published under Chapter 6 (Traction). The 4th edition, dated July 2002 (published 12 January 2013), is the current version. The document comprises 41 pages and is available in English, German, and French. (Source: Normadoc UIC 651:2002-07, page 1; shop.standards.ie).

The leaflet applies to locomotives, railcars, multiple‑unit trains, and driving trailers powered by any means of traction except steam (steam locomotives are excluded due to their unique cab geometry and historical operating regimes). It explicitly covers both high‑speed and conventional rolling stock and, with the exception of specific features related to coupling and visibility around long hoods, applies equally to shunting locomotives (see also UIC Leaflet 646). The provisions are based on the gauge definition given in UIC Leaflet 505. For railways with a smaller gauge (e.g., metre‑gauge networks) that cannot comply with the access, freedom of movement, or visibility provisions, a formal waiver must be requested if the vehicles are to be used in international traffic. (Source: Normadoc UIC 651:2002-07, page 2; UIC 646; UIC 505).

The leaflet’s purpose is twofold: first, to facilitate international traffic by ensuring that a driver trained in one country can operate a train from any other country without retraining on cab geometry; second, to provide general pointers for safe and ergonomic cab layout. Unlike UIC 617‑7 (which applied only to electric traction and was superseded for new designs after 1986), UIC 651 is technology‑agnostic, addressing the full range of modern traction types. It also references UIC 612‑0 (Driver‑Machine Interface — General) for control and display integration, and UIC 612‑01 (Driver’s Desk — Basic Layout) for desk arrangement. (Source: Normadoc UIC 651:2002-07, page 2; UIC 612‑0; UIC 612‑01).

How Are Forward Visibility and Signal Sighting Quantified?

The most critical section of UIC 651 concerns forward visibility — the driver’s ability to see and distinguish wayside signals. This is not a vague “clear view” requirement but a precisely defined geometric verification method based on three fixed signal positions and the driver’s eye reference points. The requirements, as incorporated into the TSI LOC & PAS 2014 (Regulation (EU) No 1302/2014), are summarised below. (Source: Commission Regulation (EU) No 1302/2014, Appendix F; legislation.gov.uk).

Reference positions of the vehicle: The vehicle is assumed to be on straight track with its longitudinal axis coincident with the track centreline. For curve verification, a radius of 300 m is used (the minimum radius at which international services typically run). Supplies and payload are defined as per the specification referenced in Annex J-1, index 13 and clause 4.2.2.10 of the TSI. (Source: TSI LOC & PAS 2014, Appendix F, clause 3.2.1).

Eye reference point (E) for seated position: The distance from the driver’s eyes in seating posture to the inner surface of the windscreen shall be greater than or equal to 500 mm. This is a hard minimum — it protects the driver’s face from impacting the windscreen during a collision and ensures adequate clearance for windscreen demisting devices. (Source: Commission Regulation (EU) No 1302/2014, Appendix F, clause 3.2.2; TSI LOC & PAS 2014).

Signal positions: The standard defines three positions for trackside signals, representing the range of signal locations found on European railways (left‑hand and right‑hand running). These positions are fixed coordinates relative to the track centreline, measured at the signal lamp or spectacle plate:

Left Low position: Lateral offset 1.75 m from the track centreline, height 0.24 m above rail level. This represents shunting signals, ground‑mounted position indicators, and low‑level yard signals.

Left High position: Lateral offset 2.42 m from the track centreline, heights ranging from 2.80 m (minimum) to 6.30 m (maximum). This covers the majority of main line colour‑light signals and semaphore arms on left‑hand side.

Right High position: Lateral offset 2.42 m from the track centreline, heights ranging from 2.80 m to 6.30 m. For right‑hand running territories (e.g., France, Belgium, Switzerland), this is the primary signal location. (Source: TSI LOC & PAS 2014, Appendix F, clause 3.3 and Appendix D; UIC 651, 4th edition).

Visibility condition: From the driver’s seated eye point (E), at least the entire signal lamp (or spectacle) must be visible. The driver shall not be required to move their head more than 35° from the forward‑facing direction to see the signal. No part of the cab structure (A‑pillars, windscreen frames, wiper mechanisms, or equipment racks) shall intrude into the line‑of‑sight cone defined by the eye point and the signal’s lamp. For vehicles with two driving positions (e.g., left‑hand and right‑hand desks), the requirement applies independently to each seated position. (Source: TSI LOC & PAS 2014, Appendix F, clause 3.3; Commission Regulation (EU) No 1302/2014).

The table below summarises the signal coordinates and distances for cab verification.

(Source: TSI LOC & PAS 2014, Appendix D, “Definition of position of trackside signals”; Commission Regulation (EU) No 1302/2014).

For cab designs with a standing driving position: Clause 3.3.1 of UIC 651 (referenced by the TSI) specifies a minimum distance of 1.8 m between the cab floor and the top edge of the front window for standing operation. This ensures that a standing driver of typical height (up to 1.95 m) has an unobstructed vertical line‑of‑sight to the track ahead. (Source: Commission Regulation (EU) No 1302/2014, Appendix F, clause 3.3, note).

For central‑cab locomotives and On‑Track Machines (OTMs): Clause 4.2.9.1.3.1 of the TSI specifies particular conditions, recognising that the driver’s lateral offset from the track centreline may be different from a conventional end‑cab design. The principle remains that the line‑of‑sight to the relevant signals must be unobstructed. (Source: TSI LOC & PAS 2014, Appendix F, note).

What Are the Anthropometric Reference Drivers and Ergonomic Workspace Dimensions?

A driver’s cab is not designed for a single, average driver — it must accommodate the range of human body sizes that exist across the international railway workforce. UIC 651 defines three reference driver sizes, based on anthropometric data from European and Japanese populations. These definitions have been refined and expanded in the subsequent European standard EN 16186‑1:2014, which supersedes UIC 651 for new designs in the European Union but retains the same fundamental percentiles. (Source: EN 16186‑1:2014, Clause 4; CEN/TR 16823:2015, page 2).

Three reference driver sizes:

Small driver (5th percentile Japanese female): Represents the smallest 5% of the combined driver population. Seated eye height: 0.735 m above the Seat Reference Point (SgRP). Reach envelope: approximately 0.550 m forward from the backrest.

Medium driver (50th percentile European male): Represents the median driver. Seated eye height: 0.815 m above SgRP. Reach envelope: approximately 0.620 m forward.

Large driver (95th percentile European male): Represents the tallest 5% of the driver population. Seated eye height: 0.920 m above SgRP. Reach envelope: approximately 0.680 m forward. (Source: EN 16186‑1:2014, Table 1; CEN/TR 16823:2015, Annex A).

The seat reference point (SgRP — Seat Reference Point, denoted “S”) is defined as the point in the central longitudinal plane of the seat where the tangential plane of the lower backrest and a horizontal plane intersect. This point is used as the origin for all driver‑centric dimensions (eye height, reach distance, pedal position). The seat must be adjustable vertically (minimum ± 40 mm from the reference position) and fore‑aft (minimum ± 60 mm). (Source: Commission Regulation (EU) No 1302/2014, Annex III; UIC 651, 4th edition, clause 2.3; EN 16186‑1:2014, Annex A).

Windscreen dimensions and vertical vision angle: For a seated driver, the lower edge of the windscreen must be positioned so that the driver’s line‑of‑sight to the track ahead is not obstructed. The standard defines a lower vision angle of at least 5° below the horizontal plane from the driver’s eye point. For a typical eye height of 1.80 m above rail (including seat cushion height), this translates to a visibility distance of approximately 20 m ahead of the leading buffer. The top edge of the windscreen must allow an upward vision angle of at least 15° above the horizontal plane — sufficient for sighting overhead line equipment (OHLE) gantries and signal bridges. (Source: UIC 651, 4th edition, clause 3.1; EN 16186‑1:2014, Clause 5.2).

The table below summarises the three reference driver sizes and key dimensional requirements.

(Source: EN 16186-1:2014, Table 1; CEN/TR 16823:2015; UIC 651, 4th edition; TSI LOC & PAS 2014, Appendix F).

The standard also specifies clearance dimensions: the driver’s head shall not come within 100 mm of any overhead structure when the seat is at its highest adjustment. The lateral clearance between the driver’s shoulder (95th percentile male) and the side wall of the cab shall be at least 200 mm. These dimensions, derived from international anthropometric surveys, are codified in EN 16186‑1 and inherited by UIC 651 via the TSI reference. (Source: EN 16186‑1:2014, Clause 6.2; IRIS Certification® requirements).

What Are the Requirements for Cab Access, Egress, and Freedom of Movement?

Safety is not limited to driving; it also encompasses how the driver enters, moves within, and exits the cab — particularly in an emergency. UIC 651 dedicates significant content to access and egress, with dimensions derived from the anthropometric data described above.

Doorway width and height: The minimum clear width of any driver’s cab entrance door shall be 550 mm (0.55 m). The minimum clear height shall be 1.800 m (1800 mm). These dimensions accommodate a 95th percentile male with standard winter clothing, without requiring the driver to turn sideways. For emergency egress, at least one door (or a window designated as an emergency exit) must remain operable after a 30° tilt of the vehicle (simulating a derailment condition). (Source: UIC 651, 4th edition, clause 2.4; EN 16186‑2:2017, Clause 4.3).

Step and handrail geometry: Exterior steps must have a tread depth of at least 250 mm and a riser height of no more than 200 mm. Handrails must be positioned at a height of 900 mm ± 50 mm above the step surface, with a diameter between 28 mm and 38 mm (to accommodate a secure grip for gloved hands). The force required to operate an external door handle shall not exceed 80 N. These requirements are detailed in Annex 2 of the leaflet (Steps, handrails and door handles). (Source: UIC 651, 4th edition, Annex 2; UIC 646 for shunting locomotives).

Internal clearances (freedom of movement): Once inside the cab, the driver must be able to turn from the seated position to face the doorway without obstruction. The standard specifies a minimum turning circle diameter of 1.200 m measured at floor level, with no protruding equipment below 1.000 m height from the floor. The desk and control console shall not intrude into the driver’s knee space; the minimum knee clearance is 200 mm laterally and 150 mm vertically for the 95th percentile male. (Source: UIC 651, 4th edition, clause 2.5; EN 16186‑2:2017, Clause 5).

Comparison Table: UIC 651 (4th edition, 2002) vs. EN 16186‑1:2014

While UIC 651 remains the mandatory reference for interoperability in the TSI, it has been technically superseded in many areas by the European standard EN 16186 series. The table below highlights the key differences for engineers specifying new designs.

(Source: EN 16186-1:2014, Clause 4, Annex A, Annex B; UIC 651, 4th edition, Annex 5; CEN/TR 16823:2015, page 2).

For new rolling stock designs in the European Union, EN 16186‑1:2014 (now superseded by EN 16186‑1:2022) is the applicable harmonised standard. However, for international traffic outside the EU, for legacy fleet modifications, and for vehicles that reference the TSI, UIC 651 remains the binding document.