Executive Summary

An Empa study funded by the Federal Office for the Environment shows that plug-in hybrids drive electrically far less under realistic everyday conditions than stated in type approvals. Researchers tested twelve current models on a dynamometer under various temperatures and driving profiles. The results demonstrate: Low temperatures, activated heating, and dynamic driving significantly reduce electric range and increase fuel consumption and emissions. Vehicle weight, battery size, and charging behavior play decisive roles in actual efficiency.

People

Topics

  • Plug-in hybrid technology
  • Electromobility
  • Vehicle emissions
  • Type approval procedures
  • Swiss mobility data

Clarus Lead

The study reveals a regulatory weakness: The so-called "Utility Factor" in EU approval regulations is based on outdated US commuter data and significantly overestimates the electric driving share. National mobility data for Switzerland yields a tendency toward a higher factor – but without reliable charging behavior data, uncertainties remain. These findings are crucial for future regulation: Overly conservative assumptions could unintentionally weaken plug-in hybrids as a transition technology, while realistic standards would reflect their actual environmental impact.

Detailed Summary

Empa researchers closed a methodological gap left by previous studies. While "On-Board Fuel Consumption Monitoring" (OBFCM) data from European vehicles show that real consumption exceeds type approval values, information about the causes was lacking: ambient temperature, heating use, and driving style were not recorded. In laboratory tests under controlled conditions – 23 degrees, minus 7 degrees, and minus 7 degrees with heating – as well as with more dynamic driving profiles, the isolated effect of these factors could be measured for the first time.

The results show a consistent pattern: Under ideal conditions, plug-in hybrids function as planned. In reality, however, cold and heating significantly reduce electric range, the combustion engine switches on earlier, and emissions sometimes increase substantially. Vehicle design amplifies this effect: lighter vehicles with moderate engines and balanced battery size achieve better efficiency values than heavy models. Oversized batteries only realize their advantage with regular charging and matching driving profiles, while their additional weight permanently increases energy demand.

Particularly relevant is the recalculation of the "Utility Factor" for Switzerland. The EU adjusted its methodology in 2025 and plans a further adjustment from 2027 onward, after European OBFCM data showed that the electric share falls significantly below previous assumptions. Empa researchers calculated a Switzerland-specific factor for the first time based on national micro-census mobility data. The result: An adjusted Utility Factor would be higher than the European one, since Switzerland has shorter average daily driving distances and a lower proportion of company vehicles – which are rarely charged in Europe. However, a critical uncertainty remains: The calculations assumed daily charging of vehicles without having real charging behavior data.

Key Statements

  • Plug-in hybrids show significantly lower electric range under realistic conditions (cold, heating, dynamic driving) than in type approvals
  • Vehicle weight, battery size, and regular charging are critical success factors for actual efficiency
  • The EU "Utility Factor" was based on outdated data; a Switzerland-specific calculation yields tendency toward higher values
  • Overly conservative regulatory assumptions could unintentionally weaken the transition technology

Critical Questions

  1. Evidence Quality: How representative are the 12 test vehicles for the European market? Were models from all price classes and manufacturers included?

  2. Charging Behavior Assumptions: The Swiss Utility Factor calculation assumes daily charging – what evidence supports this assumption for private users and fleet operators?

  3. Temperature Scenarios: Why were only three temperature profiles tested? How do transitional seasons or extreme values affect results?

  4. Regulatory Consequences: If the Utility Factor is increased, could this lead to better official consumption values – is there a risk that buyers will again be misled by overly optimistic expectations?

  5. Fleet Behavior: How reliable are European OBFCM data on actual charging behavior of company vehicles, which served as reference for the Swiss calculation?

  6. Battery Size Trend: Will larger batteries (and thus heavier vehicles) become more common in the future – and does this exacerbate efficiency problems?

Source Directory

Primary Source: Plug-in Hybrids: Empa Study on Real Consumption and Emissions – news.admin.ch, 16.07.2026

Supplementary Sources:

  1. Sandoval Guzmán, B. et al. (2025). Environmental performance of plug-in hybrid electric vehicles: Impacts of driving cycles, ambient temperature, and auxiliary loads. Atmospheric Environment: X. doi: 10.1016/j.aeaoa.2025.100393
  2. Sandoval Guzmán, B. et al. (2026). Utility factor frameworks for plug-in hybrid electric vehicles: A comparative assessment. Transportation Research Part D: Transport and Environment. doi: 10.1016/j.trd.2026.105098

Verification Status: ✓ 16.07.2026

This text was created with the support of an AI model. Editorial Responsibility: clarus.news | Fact-Check: 16.07.2026