FOI 26-175 Electric Hybrid Vehicles in SAS

Freedom of Information Request

Reference
FOI 26-175 Electric Hybrid Vehicles in SAS
Request Date
02 Apr 2026
Response Date
01 May 2026
Information Requested

Scottish Ambulance Service have received new electric and hybrid vehicles to replace older diesel rapid response units.

Can you please tell me why the new ambulance service rapid response vehicles have a much quieter siren than ambulances and older rapid response vehicles? they are hidden in an insulated plastic box in the front trunk which restricts the sound.

What are the decibel levels of the new and old vehicles?

The new vehicles also no longer have wig-wags during day light driving whereas older vehicles did. Why has this been removed?

Lastly, the newer vehicles no longer have the option of activating rear-reds only on the new console. Why has this been removed?

Why were these functions previously seen as necessary and now are not? What assessments and consultations have taken place before these were all removed and changed

Response

Can you please tell me why the new ambulance service rapid response vehicles have a much quieter siren than ambulances and older rapid response vehicles? They are hidden in an insulated plastic box in the front trunk which restricts the sound.

The Scottish Ambulance Service can confirm that the siren specification and output on new rapid response vehicles has not changed. All emergency response vehicles are fitted with a 100W siren system, which is compliant with the Road Vehicles (Construction and Use) Regulations 1986.

The 100 watt (8 ohm) speaker driver is mounted within a storage pod located under the bonnet. This is paired with a siren pipe extension which directs sound output forward from the vehicle. This design supports forward projection of the audible warning while reducing noise within the vehicle cabin.

The Service does not hold recorded information confirming that the positioning of the speaker restricts or reduces the external sound output. The design reflects standard vehicle conversion arrangements.

What are the decibel levels of the new and old vehicles?

The Service does not hold specific comparative decibel recordings between new and older vehicles.

However, the design specification and output of the siren systems have not changed. It should be noted that measured sound levels in operational environments can vary depending on a range of external factors including vehicle design, positioning, surrounding infrastructure (e.g. buildings), road surface, and weather conditions.

A short-term internal review is currently underway to better understand siren performance across different vehicle types. This work is ongoing and conclusions are not yet available.

The new vehicles also no longer have wig-wags during day light driving whereas older vehicles did.

Why has this been removed?

You clarified that this refers to alternating flashing headlamps.  The Scottish Ambulance Service can confirm that this functionality has not been removed from vehicles where it is already fitted.

For newly built vehicles, specifications have evolved in line with modern vehicle design. Contemporary vehicles utilise LED lighting systems and electronic Controller Area Network (CAN bus) systems to manage lighting functions. These systems can limit or prevent modification of headlamp behaviour without impacting vehicle systems, reliability, or component integrity.

All lighting configurations remain compliant with:

  • The Road Vehicles Lighting Regulations 1989 (as amended)
  • Relevant European standards (CEN)
  • BS EN 1789:2020+A1:2023 (Road ambulances and their equipment)

Lastly, the newer vehicles no longer have the option of activating rear-reds only on the new console.  Why has this been removed?

Newer vehicles do not include a standalone function to activate rear-facing red lights only.

This is because such functionality does not form part of standard operational requirements. When a vehicle is being used to protect a scene or personnel, it is required to display blue warning lights providing 360-degree visibility.

When stationary with the handbrake applied, the “Arrive Scene” function activates the appropriate combination of rear red flashing lights alongside compliant blue lighting. When the vehicle is in motion, flashing rear red lights must not be displayed.

Simplifying control systems supports:

  • Correct and consistent activation of lighting
  • Reduced operational complexity
  • Improved reliability of equipment
  • Reduced installation and maintenance costs

Why were these functions previously seen as necessary and now are not?

These functions were not operationally required but provided additional flexibility in limited circumstances.

For example, selective activation could support maintenance checks of individual light functions. However, this level of control is not required for operational use and has been superseded by simplified system design.

 What assessments and consultations have taken place before these were all removed and changed?

Vehicle design and specification decisions are informed through engagement with:

  • Emergency warning equipment suppliers
  • Vehicle conversion specialists
  • Benchmarking with other UK emergency service organisations

The Service does not hold a single formal consultation document covering all of the changes described, but decisions are made as part of ongoing fleet design, procurement, and compliance processes.

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