If you have not paid vignette charge for the use of the paid road network, you are an infringer and are subject to penalty.
The fine is typically up to 150 € or compensatory fee typically about 36 €: a lower amount you can pay on the spot to avoid further proceedings.
If the infringer pays for the compensatory charge immediately after determination of the infringement or within 14 days after drawing up of the act for determination of administrative infringement, then he will be exempt of administrative-criminal liability and will not be subject to a penalty which is of higher amount.
Additionally an e-vignette has to be purchased immediately to continue driving on Bulgarian toll roads.
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Which roads require a Bulgarian motorway vignette?
Can I drive until the first exit on the highway in Bulgaria without a vignette?