Small Buses and Their Electromagnetic Radiation

Small buses (including electric minibuses, hybrid shuttles, and compact diesel vans) have become a core part of urban mobility. These types of vehicles are used for school transport, short-range public transit, and community services. As cities adopt cleaner and smarter transportation systems, the number of battery-electric and hybrid small buses on the road continues to grow.

This development brings with it increased focus on electromagnetic radiation (EMR) inside the cabin. Unlike exhaust fumes, EMR cannot be seen or smelled. It comes from the electrical and wireless systems used for propulsion, communication, and control. Most of the time, these levels stay within international safety guidelines. However, the issue of cumulative exposure is now being looked at more closely, specifically for drivers and passengers who are exposed to these fields daily, often for extended periods.

For groups such as schoolchildren and elderly passengers (who may spend long hours in these vehicles) the need to better understand EMR exposure becomes especially important. Managing this exposure is part of the broader goal of keeping transportation safe.

Electromagnetic Radiation in Vehicles

Radiation inside vehicles is not a single type. It includes a range of frequencies generated by different systems. The most common categories are:

• Static Magnetic Fields (SMF): These are constant magnetic fields produced by direct current (DC) flow in the batteries and by permanent magnets in motors. The field strength is highest close to battery packs or high-voltage cables, especially when charging.
• Extremely Low Frequency (ELF) Fields: These fields come from alternating current (AC) systems, typically from inverters, traction motors, and power electronics. The frequency range is usually below 300 Hz. ELF fields tend to peak at locations close to floor panels above the drivetrain.
• Intermediate Frequency (IF) Fields: These are created by switching devices such as wireless charging systems and onboard power converters. Their frequency falls in the range between 300 Hz and 10 MHz. These fields are less researched but increasingly present in modern designs.
• Radiofrequency (RF) Fields: These higher-frequency fields are emitted by communication systems, including GPS modules, cellular antennas, Wi-Fi routers, and fare collection systems. RF exposure occurs mostly in the MHz to GHz range.

Sources of EMR in Small Buses

Several onboard systems contribute to the EMR environment within small buses. These include:

• Electric motors and drive units, which are major sources of ELF radiation, particularly in vehicles where motors are located underfloor or at the rear axle (source: Hareuveny, R., et al. (2015)).
• Battery Management Systems (BMS), which monitor and balance high-voltage battery modules. These systems can produce ELF and IF fields during operation and charging cycles (more from Magility’s experiment).
• HVAC systems and seat heaters, which may generate strong local ELF fields, especially near the seat base or floor-level ducts (source: JRC Policy Report).
• Infotainment and connectivity equipment, including passenger Wi-Fi routers and entertainment screens. These produce RF radiation throughout the cabin (read NCI Fact Sheet).
• Wireless payment and ticketing terminals, which are commonly installed near entry points and contribute both RF and IF emissions during use (details from Safe Accessories 2024 report).

Each of these components adds to the electromagnetic environment within the vehicle. The combined effect (and its possible health implications) is a subject now being examined by regulators, researchers, and manufacturers alike.

Car Type Focus: Small Buses

Definition and Classification

Small buses generally fall into three categories based on propulsion technology and associated electromagnetic field (EMF) characteristics:

Diesel-powered minibuses

These are conventional internal combustion vehicles. Electromagnetic radiation is limited to standard automotive electronics. No significant magnetic field exposure beyond baseline levels is expected (source: Hareuveny, R., et al. (2015)).

Hybrid small buses

These combine electric motors with fuel engines. Magnetic fields arise from the electric drive system. Exposure varies depending on system design and the operational phase: electric-only mode vs. combustion-driven (more from BfS (2009), Magnetfelder alternativer Antriebskonzepte).

Battery-electric small buses

These use large battery packs to power electric motors exclusively. They are associated with the highest levels of low-frequency magnetic fields, particularly in the extremely low frequency (ELF) and intermediate frequency (IF) ranges, due to high current flow and switching electronics (more from Gryz K, et al. (2022)).

Operational Differences

Diesel variants show minimal EMF activity during operation, while hybrid buses show fluctuating field levels depending on mode of propulsion and drive cycle. And battery-electric units? They produce consistent electromagnetic signatures both while in motion and during charging cycles.

Driving conditions affect the EMF profile. In dense urban routes with frequent acceleration and regenerative braking, field intensity tends to spike repeatedly. In contrast, longer rural routes with smoother driving patterns result in more stable, continuous exposure levels.

Scientific Measurements and Exposure Levels

Measurement Techniques

To assess electromagnetic radiation (EMR) inside buses, several measurement methods are used:

• ELF and RF Field Meters: These instruments capture either momentary (spot) values or trends over time. They are deployed at various points inside the bus cabin to track exposure patterns (read more from SafeFields Technologies 2024 report)
• Personal Dosimeters: Small devices worn by drivers or passengers that log individual exposure to electromagnetic fields throughout the ride (JRC Policy Report).
• Onboard Field Mapping: This involves mounting sensors within the cabin to continuously monitor real-time changes in exposure levels under normal driving conditions (used in Magility’s experiment).
• Stationary Measurements: Conducted in test labs, often with the bus placed on a chassis dynamometer to simulate typical driving scenarios without motion-related noise.

Each method gives a different perspective. Some focused on peak values, others on the range and fluctuation over time.

Exposure Levels in Small Buses

In small electric or hybrid buses, the strongest ELF magnetic fields are typically recorded:

• Near the vehicle floor (especially above the battery pack or high-voltage cables).
• Adjacent to the drivetrain, particularly when accelerating or during regenerative braking.

Levels can exceed 10–20 microteslas (µT) in some regions, which is significantly above typical background levels found in homes.

For RF exposure, peaks are observed near:

• Wi-Fi access points and antenna systems.
• Driver interface systems, including GPS, communication modules, and digital fare terminals.

When contactless ticketing is active (particularly during boarding), RF spikes are measurable at close range to payment devices.

Variation by Seating Location

Field strength depends heavily on where a person is seated. Several recurring patterns are noted:

• Front of the Bus: RF exposure is typically highest here, driven by proximity to the driver’s electronics console and roof-mounted antennas.
• Mid-Cabin Seats: Usually experience the lowest combined EMF exposure. Fewer high-voltage components and electronics are nearby.
• Rear Seats: May register elevated ELF levels, especially in configurations where the electric motor or battery is mounted beneath or behind the rear row.

Special attention is warranted in school minibuses, where children seated in rear positions or above battery housings may experience exposures higher than the average passenger. Seat placement and underfloor component layout become critical factors in exposure risk.

Case Studies and Scientific Research

Top Research Examples

1. A comparative study examining hybrid, diesel, and gasoline vehicles found that extremely low frequency (ELF) magnetic fields were highest in hybrids. These fields were particularly higher near the driver’s seat and floorboard areas.
2. A policy paper issued by the European Commission assessed electromagnetic field (EMF) levels inside electric vehicles. The report concluded that although measured exposures typically stayed within ICNIRP guidelines, long-term health implications remain unclear.
3. Controlled tests in Germany identified specific areas within electric vehicles where magnetic field strength was highest. These “hotspots” often appeared in the trunk, back seat, or driver’s footwell, depending on battery location and cable routing.
4. Animal-based laboratory studies explored the biological effects of magnetic field exposure typical of electric vehicles. Findings showed possible effects on immune system behavior and body weight regulation. These results are not yet conclusive and call for more long-term research.

Notable Results

1. Measurements inside electric minibuses showed consistently higher ELF levels compared to diesel-powered models, especially in regions close to the battery system.
2. Wi-Fi-equipped buses recorded higher radiofrequency (RF) emissions, with levels increasing during idle time and charging.
3. Magnetic field peaks were recorded during charging events, particularly around cable connectors. These peaks included both static magnetic fields (SMF) and ELF components and occasionally exceeded 100 microtesla (µT) in close proximity.

Health and Safety Considerations

Scientific understanding of electromagnetic radiation (EMR) and its effects on health is still developing.

The World Health Organization (WHO), after reviewing multiple studies, classified extremely low-frequency (ELF) magnetic fields as “possibly carcinogenic to humans.” This classification is based on observed links between ELF exposure and a higher chance of childhood leukemia.

The U.S. National Cancer Institute has clarified that these fields are non-ionizing and do not directly damage DNA like X-rays do. However, long-term or strong exposure may still affect how biological systems function.

The BioInitiative Report, a review of hundreds of studies, points out that even low-level exposure to EMFs can influence stress responses, immune activity, and the nervous system. These changes happen at levels well below most current safety limits.

People who are more sensitive to health risks (children, pregnant women, or professional drivers exposed daily) are considered higher-risk groups and may require additional precautions.

Electrified Small Buses: Urban Mobility with EMR Considerations

The compact designs of electrified small buses, along with high-density electronics, create unique electromagnetic environments.

Measurements show that EMR levels in minibuses often stay below international safety limits. However, field mapping has identified certain areas (near powertrain components like batteries, inverters, and wireless routers) where exposure can spike.

There is still a lack of long-term studies on health outcomes from regular EMF exposure in such vehicles, particularly for young passengers or frequent drivers. In light of this, experts recommend practical safeguards: better shielding, smart component placement, and limiting EMF-intensive features near seating areas.

Precaution does not conflict with innovation. As cities invest in clean transportation, the design of small electric buses must balance efficiency with health standards to ensure that the transition to greener mobility does not come with unintended health trade-offs.

References

1. World Health Organization (2007). Extremely Low Frequency Fields: Environmental Health Criteria 238.
2. National Cancer Institute (2022). Electromagnetic Fields and Cancer
3. Gryz K, Karpowicz J, Zradziński P. (2022). Complex Electromagnetic Issues Associated with the Use of Electric Vehicles in Urban Transportation
4. Hareuveny R, Sudan M, et al. (2015). Characterization of Extremely Low Frequency Magnetic Fields from Diesel, Gasoline and Hybrid Cars under Controlled Conditions
5. European Commission Joint Research Centre (2020). Assessment of Low Frequency Magnetic Fields in Electrified Vehicles
6. Bundesamt für Strahlenschutz (German Federal Office for Radiation Protection) (2009). Bestimmung der Exposition durch Magnetfelder alternativer Antriebskonzepte: Abschlussbericht zum Forschungsvorhaben
7. BioInitiative Working Group. (2012). BioInitiative Report: A Rationale for Biologically-Based Public Exposure Standards
8. Magility (2023). Electromagnetic Fields in Cars – An Experiment
9. Safe Accessories (2024). That radiation from electric cars can be dangerous?
10. Ahlbom A, Day N, et al. (2000). A Pooled Analysis of Magnetic Fields and Childhood Leukemia. British Journal of Cancer
11. SafeFields Technologies (2024). Reducing Magnetic Fields Exposure of Electric and Hybrid Cars
12. Zhang, W., Wu, J., Lin, Y., & Xu, J. (2021). Biological experimental study on cumulative effect of vehicle electromagnetic radiation