What is the maximum permissible length of a car towing a trailer?

Verified 14 March 2022 - Directorate for Legal and Administrative Information (Prime Minister)

The combination of vehicles (car + trailer) shall not exceed 18 meters.

The trailer must not overtake 12 meters (excluding coupling device).

Failure to comply with these rules is punishable by a fine of up to €750.

In general, it is a flat-rate fine of €135.

However, if the overrun exceeds the permitted limit by more than 20 %, the fine may be up to €1,500.

FYI  

the width maximum permissible for a car, as for its trailer, is 2.55 meters.