A road tube is a traffic counting device used on roads. It is a long rubber tube placed across a road that can count the number of vehicles passing over it.

When a vehicle drives over the tube, the air inside is compressed, creating a pulse that is recorded by a counter. This allows counting of vehicles as well as their speed.

https://static.la-toulousaine.com/fr/documentation/file/64

https://static.la-toulousaine.com/fr/documentation/file/534

It looks something like this:
https://pro.la-toulousaine.com/fr/produit/tube-routier

There are several articles posted wherein the use of road tube is mentioned. Something like this: https://www.tdg.ch/appui-consolide-au-2e-tube-routier-au-got...

When you'll google it, you'll find many more articles wherein this term has a mention to a large audience.

I hope this helps! Happy translating! :-)

At least that's what's given in the Dictionnaire Technique des Routes et de la Circulation Routière of PIARC (Assoc. Internat. Permanente des Congrès de la Route - AIPRC), published by La Maison du Dictionnaire in 1992.

PIARC's online dictionary https://www.piarc.org/fr/activites/Dictionnaire-Routier-Term... gives tube pneumatique (which out of context is unclear), defining it as ube de caoutchouc qui répond au passage d'une roue ou d'un essieu par émission d'une impulsion d'air sous pression and giving tube de comptage routier (meaning more immediately obvious) as a synonym.

Tube comptage routier 12 mm
https://www.techni-contact.com/produits/2622-15055100-tube-c...

tube de comptage routier en caoutchouc - https://www.dardonville.fr/produits-hydrauliques-produits-pn...