**Andrzej Czy ˙zewski, Józef Kotus and Grzegorz Szwoch \***

Telecommunication and Informatics, Multimedia Systems Department, Faculty of Electronics, Gdansk University of Technology, Narutowicza 11/12, 80-233 Gda ´nsk, Poland; ac@pg.edu.pl (A.C.); jozef.kotus@pg.edu.pl (J.K.) **\*** Correspondence: grzszwoc@pg.edu.pl

Received: 15 November 2019; Accepted: 25 December 2019; Published: 29 December 2019

**Abstract:** Innovative road signs that can autonomously display the speed limit in cases where the traffic situation requires it are under development. The autonomous road sign contains many types of sensors, of which the subject of interest in this article is the Doppler sensor that we have improved and the constructed and calibrated acoustic probe. An algorithm for performing vehicle detection and tracking, as well as vehicle speed measurement, in a signal acquired with a continuous wave Doppler sensor, is discussed. A method is also experimentally presented and studied for counting vehicles and for determining their movement direction by means of acoustic vector sensor application. The assumptions of the method employing spatial distribution of sound intensity determined with the help of an integrated three-dimensional (3D) sound intensity probe are discussed. The enhanced Doppler radar and the developed sound intensity probe were used for the experiments that are described and analyzed in the paper.

**Keywords:** Doppler sensor; acoustic vector sensor; road traffic monitoring
