Where are road sensors located?

Road sensors are located across the transportation network—embedded in pavement, mounted on roadside poles and gantries, and placed along highways and at major interchanges.

They serve various purposes, from monitoring traffic flow and speeds to detecting incidents, weather conditions, and road surface status. Placement strategies depend on the sensor type and the data needs of traffic operators and planners.

Common installation locations

Road-sensing equipment is typically grouped into two broad installation categories: pavement-embedded devices that sit directly in or under the roadway, and overhead or roadside installations that watch traffic from above or along the verge. Each category has standard examples used worldwide.

Pavement-embedded sensors

• Inductive loop detectors installed in asphalt or concrete at intersections and mid-block to count vehicles and measure occupancy.


• Magnetic or piezoelectric sensors embedded in the road to detect presence and sometimes speed and vehicle class.


• Old-style pneumatic tube detectors installed in lanes for vehicle presence (being phased out in many places but still in use in some networks).


• Friction/temperature sensing elements integrated into pavements in some regions to monitor surface conditions and road texture (often part of broader road condition programs).

Overhead and roadside installations

• Radar and lidar sensors mounted on gantries, poles, or roadside structures to measure speed, distance, and vehicle type without direct contact.


• Video camera systems for traffic monitoring, flow estimation, and incident detection; data may be processed locally or fed to centralized traffic-management centers.


• Road-weather and environmental sensors on poles or in dedicated weather stations to monitor temperature, humidity, wind, precipitation, and road-surface conditions.


• Tolling infrastructure sensors and gantries that classify vehicles, read transponders, and collect toll-related data.

These installations are complemented by other devices such as roadside magnetic sensors and sometimes embedded fiber-optic sensors in some specialized networks. The exact mix depends on national standards, traffic goals, budget, and privacy considerations.

Data types and usage

Once collected, sensor data are processed and transmitted to traffic management centers, with outputs used to adjust signal timings, issue traveler information, and support safety and maintenance decisions. The following data types are commonly harvested from road-sensor networks.

• Vehicle counts, speeds, occupancy, and vehicle classification (cars, trucks, buses) from loops, radar, or classification cameras.


• Flow and congestion metrics, travel times, and incident detection derived from aggregating multiple sensors.


• Video-derived metrics for real-time monitoring and traffic analytics, with privacy protections where required.


• Weather and road-surface conditions (temperature, precipitation, icing risk) from road-weather stations.


• Environmental data such as air quality from urban sensors along major corridors.

Data integration supports dynamic signal control, traveler-information systems, and long-term planning, with privacy and security standards varying by jurisdiction.

Summary

Road sensors are located throughout the road network—under pavement at intersections, along corridors on gantries and poles, at toll facilities, in tunnels and bridges, and in roadside weather stations. They come in various types designed to measure traffic flow, speeds, vehicle types, weather, and condition of the road surface, feeding centralized systems that manage traffic and inform travelers.

Where are traffic light sensors located?

Traffic light sensors are located either under the road's surface in the form of inductive loops, or above ground as cameras, radar, or infrared sensors mounted on poles or on the traffic light itself. Inductive loops are buried in the asphalt, often marked by white or gray lines, and detect vehicles as they drive over them. Cameras and other above-ground sensors provide a view of the intersection to detect vehicles and pedestrians.
 
Under the road

• Inductive loops: These are wires buried in the road, typically in a loop or rectangular shape, that act as a magnetic sensor. When a large metal object like a vehicle drives over the loop, its inductance changes, which triggers the sensor. You can often see the faint outline of these loops in the pavement at stop lines.
• Position: Loops are often placed just before the stop line to detect waiting vehicles, and sometimes further back on faster roads to give the signal more time to change. 

Above ground

• Cameras: Video cameras are frequently mounted on poles above the intersection, looking down at the lanes. These use image recognition to detect vehicles. Some of these are specifically red-light cameras, which are positioned to see if a vehicle crosses a stop line when the light is red. 
• Radar and infrared sensors: These are often seen as boxes or long antennae mounted on poles above the roadway. They detect vehicles by using microwaves to sense disturbances in a magnetic field or by picking up the heat signature from a vehicle's engine. 
• Emergency vehicle preemption: Tiny black infrared devices on the side of traffic lights have a corresponding device on emergency vehicles. When activated, they allow emergency vehicles to get a green light to pass through the intersection quickly. 

Are there sensors under roads?

Yes, there are sensors under the road, most commonly in the form of inductive loops used for traffic lights and detection. These are wire coils buried beneath the pavement that detect a vehicle's presence by sensing a change in the magnetic field when a large metal object like a car drives over them.
 
How they work

• Magnetic detection: When a car drives over the loop, the vehicle's metal body alters the loop's inductance, which is measured by the traffic signal controller. 
• Triggering lights: This change signals the traffic signal to change, or a specific light, like a turn arrow, to become active. 
• Placement: The loops are typically placed in each lane where a vehicle would stop or wait. 

Limitations and alternatives

• Older technology: Inductive loops are an older technology and are sometimes no longer installed in new intersections because they can be destroyed during road repairs. 
• Motorcycle/bicycle issues: They can have difficulty detecting motorcycles or bicycles because they are not large enough to cause a significant enough change in the magnetic field. 
• Modern alternatives: Newer technologies, such as radar and video detection cameras mounted on poles or towers above the road, are also used to detect vehicles and are not subject to the same limitations. 

Where are sensors located in a car?

Car sensors are located throughout the vehicle, including at the engine (like the oxygen and coolant temperature sensors), under the hood (like the mass air flow sensor), on the wheels (for anti-lock brakes and speed), around the bumpers (for parking assistance), and in the exhaust system (oxygen sensors). Different sensors monitor various functions, from engine performance and emissions to safety features like airbags and parking assistance.
 
This video explains the location of the four main engine sensors: 0:44P3KCARSFacebook · Sep 9, 2024
Engine and under the hood

• Oxygen Sensor: Located in the exhaust system, either near the exhaust manifold or directly in it, and sometimes a second one after the catalytic converter. 
• Coolant Temperature Sensor: Found on the engine block or near the thermostat housing. 
• Mass Air Flow (MAF) Sensor: Situated between the air filter and the intake manifold. 
• Knock Sensor: Attached to the engine block, near the cylinders. 
• Crankshaft and Camshaft Position Sensors: Positioned near the crankshaft or camshaft, respectively, at the bottom or top of the engine. 
• Manifold Absolute Pressure (MAP) Sensor: On the intake manifold, connected by bolts or a vacuum hose. 

Wheels and chassis

• Wheel Speed Sensors (ABS): Mounted on or near the wheel hubs at each wheel. 
• Tire Pressure Monitoring System (TPMS) Sensors: Inside each wheel assembly, often on the valve stem. 
• Crash Sensors: Located in the front of the car, behind the bumper, and also in the side pillars or doors. 
• Yaw Rate Sensor: Part of the stability control system, found on the chassis. 

Bumpers and exterior

• Parking Sensors: Embedded in the front and rear bumpers. 
• Radar Sensors: Often found in the front and rear bumpers for adaptive cruise control. 
• Rain Sensor: Located on the inside of the windshield. 
• Outside Temperature Sensor: Usually mounted under the front of the hood near the bottom of the car. 

This video provides a 3D animation of how car sensors work: 56sCARinfo3d (En)YouTube · Sep 29, 2024

What is a road sensor?

Road condition sensors: A critical component of any road weather information system (or RWIS) is a set of road condition sensors that measure surface temperature and moisture, and detect the presence and thickness of snow and ice. Road condition sensors can be embedded in the pavements.