What is the purpose of UIC Leaflet 644?

UIC Leaflet 644 sets the technical standards for acoustic warning devices (horns) on locomotives used in international rail services, ensuring they are audible and recognizable across different countries.

How loud are train horns according to regulations?

Train horns are extremely loud to ensure safety. While specific values vary by version, they typically generate sound pressure levels between 100 dB and 125 dB at a distance of 5 meters.

Has UIC 644 been replaced?

In the European Union, UIC 644 has largely been superseded by the TSI LOC&PAS (Technical Specifications for Interoperability for Locomotives and Passenger Rolling Stock), though it remains a valid reference in non-EU regions.

The Voice of the Locomotive: Understanding UIC Leaflet 644

UIC Leaflet 644 defines the acoustic warning devices (horns) for international trains.[1] Learn the technical standards for sound pressure, frequencies, and audibility.

September 21, 2023 3:16 am

What is UIC Leaflet 644?

UIC Leaflet 644, titled “Warning devices used on tractive units employed on international services,” is a technical standard established by the International Union of Railways (UIC). It specifies the requirements for the acoustic signals (horns and whistles) installed on locomotives and trainsets.

The primary goal of this leaflet is to ensure Interoperability and safety across borders. A train traveling from France to Germany must have a warning device that is recognizable and effective in both countries. While modern European regulations are shifting towards the TSI LOC&PAS (Technical Specifications for Interoperability), UIC 644 remains a fundamental reference for rolling stock manufacturers worldwide.

Technical Requirements of the Warning Device

The standard dictates how a train must sound to be audible to track workers and the public at level crossings, without causing permanent hearing damage.

Dual Tones: The warning device typically consists of two distinct tones (notes) that can be sounded separately or together (a chord). This distinctive “two-tone” sound helps distinguish trains from road vehicles.
Sound Pressure Level: UIC 644 specifies a high sound pressure level, generally measured at a reference distance (e.g., 5 meters). This ensures the horn can be heard over long distances, even in adverse weather conditions.
Reliability: The device must function reliably under extreme conditions, including freezing temperatures and high speeds where air pressure dynamics change.

Comparison: UIC 644 vs. TSI LOC&PAS

In the European Union, the technical standards have evolved from UIC leaflets to mandatory TSIs. The table below highlights the shift in focus regarding acoustic warnings.

Parameter	UIC Leaflet 644 (Legacy/Global)	TSI LOC&PAS (Modern EU Law)
Primary Focus	Maximum audibility for safety	Balance between safety and noise pollution
Tone Frequency	Specific musical intervals required	Standardized frequency ranges (High/Low)
Sound Pressure (Max)	High limits (often >120 dB)	Strictly capped (typically 125 dB max) to protect hearing
Activation	Pneumatic or electric	Integrated into Driver Machine Interface (DMI) logic