Density-Based Statistical Clustering: Enabling Sidefire Ultrasonic Traffic Sensing in Smart Cities

Table 1

Overview of state-of-the-art traffic monitoring techniques.

Sensing technology	Characteristics (/)	References
Infrastructural sensing techniques
Infrared sensors; (passive and active)	Vehicle class and speed information acquisition is possible	[10, 11]
	Multilane operation possible (active sensors)
	Susceptible to bad weather conditions
	Regular cleaning required (active sensors)
Camera-based systems	High detection and classification accuracy	[6, 7]
	Privacy and authorization issues
	Susceptible to bad weather and light conditions
In-pavement sensors; (inductive, piezoelectric, and strain)	High detection accuracy with axle counting	[8, 9]
	Invasive and costly installation due to in-pavement integration
Directional high-end radar sensors	Multilane multiobject traffic participant detection	[10, 12, 13]
	Directional and velocity information
	Cost and complexity of solutions
Top-down ultrasonic and radar sensors	Low cost and simple mode of operation	[10, 14–18]
	Only single-lane operation
	Mounting above lane required, for example, on sensor gantry
Proposed sidefire ultrasonic sensing	Multilane operation possible
	Sidefire mounting allows seamless integration into environment
	No directional information available in sidefire configuration
User-based distributed traffic monitoring techniques
Crowdsourcing systems; (smartphones and navigation devices)	High number of devices	[21–23]
	Privacy concerns
	Susceptibility to attacks and data manipulation
V2X-based cooperative systems	Combination with in-vehicle information and decisions	[24]
	Low support and prevalence