Probe vehicle data is currently generated using satellite navigation systems such as the GPS, GLONASS or Galileo systems. However, because of their high cost and relatively high position uncertainty and low sampling rate, satellite positioning systems have a relatively low penetration rate among users. In addition, such sensors do not provide context in the traffic measurements. To address these issues, we introduce a new traffic monitoring concept based on inexpensive inertial measurement units in conjunction with a wireless sensor network deployed inside a city. After discussing the sensing technique, we present a preliminary implementation of this system using an open source robotic platform. Preliminary results show that this system can be used to generate traffic measurement data.