Electric Vehicles

Electric Vehicles

Key Facts:

Crashworthiness

  • The crashworthiness, also known has passive safety, of electric vehicles, differs from conventional vehicles because of the lack of an internal combustion engine (ICE) in (typically) the front compartment, the addition of battery packs and the structural modifications to the vehicle designed to cope with the associated increase in vehicle weight (Lassfolk et al., 2010).

  • The market share of small electric vehicles relative to conventional ICE vehicles may increase further in future years; this could affect accident statistics, unless improvements in the “compatibility” of different vehicle types can be achieved (Visvikis, 2012).

  • The United Nations (UN) has adopted the first international regulation (Regulation 100) on the safety of both fully electric and hybrid-electric vehicles to ensure that vehicles with a high-voltage electric power train are as safe as ICE vehicles (Visvikis, 2012).

  • Crash tests with a Mitsubishi i-MiEV electric car by ANCAP and Euro NCAP revealed no problems with the battery or the electrical system (Paine).

Post-impact safety issues

  • Electric propulsion technology carries some inherent risks which are unique to electric vehicles. Rechargeable energy storage systems (RESS) may be realised through the use of batteries, capacitors and electromechanical flywheels. Batteries, in particular, have raised a number of key safety concerns, including electrolyte leakage due to cell casing damage, chemical reaction to extreme temperature of fire, and electrical risks such as short circuit and electroshock (Visvikis et al., 2010).

  • The lithium contained within lithium ion batteries is highly reactive and the electrolytes are highly flammable. Abuse tests have identified thermal runaway, electrolyte leaks, smoke, venting, fire and explosion as potential issues with lithium ion batteries. Internal and external protection mechanisms such as fuses and flame retardants have been incorporated into lithium ion batteries by manufacturers in an attempt to reduce these risks (Pesaran et al., 2009; Tjus, 2011).

  • It may be noteworthy however that few serious incidents relating to lithium ion batteries have been reported despite extensive worldwide use over the last decade (Kalhammer et al., 2009; Pesaran et al., 2009).

  • Hydrogen is colourless, odourless, burns with a blue flame undetectable in sunlight, disperses in air faster than natural gas and gasoline vapour, is more flammable in air and has a smaller molecular structure allowing it to more easily leak through materials. These factors are crucial considerations for the post-impact safety of hydrogen fuel-cell vehicles (Visvikis et al., 2010; Rigas and Amyotte, 2013).

Risks associated with low vehicle noise emission

  • The National Highway Traffic Safety Administration (NHTSA) in the USA reported that HEVs were found to be twice as likely to be involved in a slow-moving accident with pedestrians as equivalent ICE vehicles. However, a separate study reported that the likelihood of being involved in a collision with a pedestrian was equal between EVs/HEVs and conventional ICE vehicles (NHTSA, 2009; Morgan et al., 2011).

  • Any potential increased accident risk may be attributable to the lack of engine noise emitted from electric vehicles. Development of acoustic warning signals to replace the absence of engine noise may be warranted (Brand et al., 2012).

  • Pedestrians with normal vision, blind pedestrians, and those with visual-impairments were able to detect the sound of an ICE vehicle from a distance of approximately 36m, but this reduced to 14m when detecting the sound of an EV. No information was provided on the speed of the moving vehicles, however (Altinsoy, 2013).

  • In a study which showed 24 participants a video of a moving 2007 Toyota Prius coupled with one of six categories of sound: engine, horn, hum, siren, whistle and white noise, it was found that engine noise was most preferable as an auditory cue, followed by hum sounds and white noise (Wogalter et al., 2013).

  • In a study with 15 visually-impaired participants, the addition of an approaching Vehicle Sound for Pedestrians (VSP) alert system to an HEV resulted in significantly faster and more reliable detection than an identical vehicle with no VSP system, and a conventional ICE vehicle. However there were no differences in the ability of participants to discriminate between the intended pathway of the vehicle suggesting that a VSP system may only enable faster detection of the presence of a vehicle (Kim et al., 2012).

  • Date Added: 03 Apr 2012, 08:22 AM
  • Last Update: 05 Feb 2014, 04:34 PM