Can the pressure wave from a car kill frogs?

A theoretical work by Dietrich Hummel from 2001 mathematically describes the changes in air pressure that cars exert on amphibians (Hummel 2001 ^[1]). The work assumes that amphibians that are not run over and crushed by the tires can still injure themselves and are exposed to a damaging pressure wave. This pressure wave moves at the speed of the car itself and is caused by the displacement of the air. This creates an overpressure in front of the car and a negative pressure underneath the car. The pressure difference is directly proportional to the square of the driving speed. The effect is even more pronounced in lower-seated cars. The negative pressure in particular can lead to internal injuries in amphibians. It is assumed that the negative pressure can damage lungs and even cause them to burst. Other organs, such as the tongue, can be pushed out. In an interview with NABU (“Naturschutz heute” 1st edition 2003), author Dietrich Hummel stated that speeds of even 50 km/h are generally fatal for amphibians. However, this is not consistent with other experiences and observations. Amphibians can also be run over at speeds higher than 50 km/h without suffering any health damage from the negative pressure.

No fatalities in practical examinations of cane toads in Australia

During field research on reptiles in 2016 in North Queensland (Australia), researchers accidentally ran over thousands of cane toads (Rhinella marina) without hitting them with their car tires. The researchers observed no negative effects and were therefore skeptical of Hummel’s (2001) predictions. The researchers therefore decided to conduct a practical study (Mayer et al. 2018 ^[2]). They drove over the toads in a Ford Falcon XR6 (front height 15 cm, rear height 25 cm, lowest point 9 cm) at four different speeds: 50, 80, 100, and 110 km/h. After running over the toads, the researchers stopped and collected the toads. The toads were kept captive overnight, and their survival was recorded the next day. No deaths or injuries were documented among a total of 97 toads, with 18 toads being run over at 50 km/h, 17 at 80 km/h, 21 at 100 km/h, and 41 at 110 km/h (Mayer et al. 2018 ^[2]).

Conclusion: The pressure wave from a car is often not fatal to the animals. An evasive maneuver for the animal’s well-being can certainly be advisable even at higher speeds.

Source

[1] D. Hummel, 2001: Amphibienschutz durch Geschwindigkeitsbegrenzung – eine aerodynamische Studie. Natur und Landschaft. Volume 76, Issue Nr. 12 link

[2] M. Mayer, J. A. Lyons, R. Shine, D. Natusch, 2018: Air-pressure waves generated by vehicles do not imperil road-crossing amphibians. Salamandra February 2018 link