How Automated Speed Enforcement Cameras Work

Speeding costs 400,000 lives on roads worldwide each year, according to the World Health Organization (WHO). Studies by the National Highway Traffic Safety Administration (NHTSA) show that automated speed cameras save lives and reduce enforcement costs. Speed cameras operate 24/7 without the expense and risk of personnel deployed by the roadside. But how do they work?

All speed cameras combine a mechanism for accurately measuring speed with camera functionality that gathers evidence of the violating vehicle. We can divide speed cameras based on the type of mechanism they use: 

RADAR Speed Cameras

A RADAR (Radio Detection And Ranging) speed camera measures the change in the frequency of returned radio waves to precisely measure the speed of vehicles (the Doppler effect). Though revolutionary more than 40 years ago, early Doppler speed cameras suffered from problems with accuracy and specificity of the target vehicle. Some modern RADAR speed cameras mitigate these issues with the use of sophisticated Time of Flight and triangulating radar technologies.

One of the earliest RADAR speed cameras was the Gatsometer deployed by Gatso in the UK in late 1964, which used film cameras driven by a RADAR; the film had to also be changed every day or two. Though revolutionary for the time, it was costly, complicated and inaccurate.

Pros: Precise speed measurement, ubiquitous and well-understood

Cons: May report speed for incorrect vehicles

LiDAR Speed Cameras

Modern LiDAR (Light Detection And Ranging), uses the returned time of pulsed laser light instead of radio waves (RADAR) and has become more popular due to its reliability in detecting vehicle speeds. Evolving from hand-held police speed guns in late 1980s, modern LiDAR has grown to encompass fixed-beam and scanning laser-based range and speed sensors, as well as a new breed of Time of Flight cameras. All LiDAR systems rely on successive measurements of range at precise times to calculate the speed of passing vehicles. An example of a Time of Flight speed camera is the Viion TrafficCam 3D.

Pros: Accurate, simple to deploy, mobile, user-friendly

Cons: None

Average Speed Cameras

Unlike LiDAR or RADAR, average speed cameras, also known as speed zones, don’t measure a driver’s speed at a single point in time. Instead, they work in pairs (a camera mounted at two different locations) to measure the time taken by a vehicle from a starting point to a second point further down the road.

The biggest advantage of average speed cameras is that regardless of how fast a vehicle travels when they pass the first or second camera, if their average speed exceeds the speed limit over the roadway between the cameras, they automatically receive a ticket. Average speed cameras are common throughout Europe and Australia, though they’ve seen increased interest in North American cities.

Pros: Enforces speed over an entire zone, not at a single point

Cons: Does not enforce peak speed within the zone, two cameras are required for system to work, not legal everywhere

In-road Sensors (Inductive Loop, Piezoelectric, Broken Beam, …)

In-road sensors, such as inductive loops are installed in pairs at fixed positions close together along the roadway. Combined with a precise timing computer, these sensors calculate the time taken by vehicles to move from the first set of sensors to the second set of sensors. In-road sensors are highly accurate but have a high deployment and maintenance cost and are therefore rarely used worldwide, though they are still widely popular in Brazil.

Pros: Can be used in large variety of applications, strong knowledge base

Cons: Requires cutting pavement, whether it is for installation, maintenance or replacement, wire loops are subject to stresses of traffic and temperature


Regardless of which system is chosen to enforce speed, accurate vehicle speed measurement is an ongoing challenge and none of these solutions are perfect since all have their pros and cons.  

Further Reading

Benefits and Economics of Automated Speed Cameras

Today, WHO states that speed contributes to around 50 per cent of road crashes in low-income countries and 30 per cent of deaths in high-income countries. Additionally, WHO pointed out that if we can reduce speed by just 1 km/h, we could cut traffic-related injuries world-wide by 5 per cent. This would be a significant improvement, considering that in the United States alone, NHTSA estimates that speeding-related crashes cost more than $40 billion per year.

For more information on how automated speed enforcement cameras have helped reduce fatalities and costs, please read our case studies on Speed Enforcement.

Please visit the Viion product catalogue to browse through our available speed enforcement solutions. 

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