Microwave Traffic Detector

Definition and Technical Principle

A microwave traffic detector is a non-intrusive detection device that utilises digital radar wave technology to collect real-time traffic flow data through the transmission and reception of microwave signals. Its core technology is based on the Doppler effect and Frequency Modulated Continuous Wave (FMCW) technology. In operation, the unit emits microwave signals towards the road surface via an antenna and receives reflected echoes from passing vehicles, computing the frequency difference between transmitted and reflected waves to determine vehicle speed, position, and related parameters. By employing layered scanning technology, the detection zone can be partitioned into multiple tiers (such as 32 or 254 layers), enabling real-time multi-lane and multi-target tracking and detection.

Detection Capability and Accuracy Indicators

The device can monitor traffic data across up to 10 to 12 bidirectional lanes, capturing key parameters including traffic volume, average speed, lane occupancy, vehicle classification, and headway. In terms of performance benchmarks, traffic volume detection accuracy reaches >95% for individual lanes and >98% for total volume, single-vehicle speed accuracy exceeds 97% (across a 10–250 km/h speed range), and lane occupancy accuracy stands at ≥95%. Latest-generation units can achieve a volume detection accuracy of over 98% across a 300-metre cross-section.

Core Advantages and Applicable Scenarios

As a non-intrusive solution, microwave detectors eliminate the need for road cutting unlike conventional inductive loop detectors. They are unaffected by central medians or metal guardrails, ensuring straightforward installation and maintenance. Their all-weather operational reliability offers a decisive advantage over video-based detection—maintaining stable performance through heavy rain and adverse weather, completely unaffected by ambient lighting or environmental shifts. The equipment is predominantly deployed for traffic data collection on expressways, highways, federal roads, and bridges, supplying vital data feeds for traffic signal control, dynamic message sign updates, and information dissemination systems.

Technical Limitations

Microwave detectors do face certain physical constraints. Early side-mounted units calculated vehicle speeds based on assumed fixed vehicle lengths; consequently, measurement accuracy is notably compromised on congested stretches, routes with heavy commercial vehicle traffic, or roads with varied vehicle profiles due to vehicle occlusion and length discrepancies. Furthermore, the technology is incapable of detecting stationary targets or vehicles travelling at near-zero crawl speeds. In terms of mounting requirements, the device mandates at least a 3-metre clearance from the nearest live lane, which poses installation challenges on structural road sections such as bridges and flyovers.

Technical Evolution

Since its initial commercial rollout internationally in 1989, microwave detection technology has advanced considerably. Operating frequencies have progressed from legacy K-band towards 77GHz millimetre-wave radar, driving continuous gains in detection precision. On the standards front, the updated standard "Traffic Information Collection - Microwave Traffic Flow Detector" (GB/T 20609-2023) was formally enacted in 2023, superseding the 2006 release. The prevailing industry trend centres on multi-sensor fusion—radar-video integrated systems leverage the complementary strengths of both sensors to deliver target trajectories, traffic flow analytics, and incident detection data simultaneously, and are already widely adopted in urban intersection upgrading and modernisation projects.