Carpooling is the joint use of a motor vehicle by several people and for which financial exchanges are limited to the sharing of costs (petrol, tolls).
Outside this framework, you will be prosecuted for violation of the regulations on the transport of people.
You do not have to take out additional insurance since civil liability insurance is sufficient for carpooling, but beware it does not cover all situations.
You do not risk any prosecution in the event of an offense related to the transport of luggage whose content is illegal or of a person in an irregular situation since you had no knowledge of it.
You will also not be liable if adult passengers do not fasten their seat belts, but you will be liable for a fine per unfastened passenger if they are minors.
Finally, if you use a company car to carpool, it is imperative to obtain the prior agreement of the employer.
Otherwise, he could incur sanctions or even dismissal.