Overheight Vehicle Detection: Height-Gate & Load Clearance

A height bar is a blunt instrument: it only warns a driver after the collision has started. By the time a steel beam rings, the trailer roof is already open, the load is spilled, the gate is bent, and a lane is closed for the rest of the shift. Overheight vehicle detection moves that moment earlier — estimating vehicle height from video well before the constraint, and warning the driver or holding the barrier while there is still somewhere else to go.

Height and load clearance are standard concerns in transport engineering, covered within the Intelligent transportation system framework, and the electrical and signalling equipment used at controlled gates falls under standards maintained by the IEC.

The Damage Is Not Proportional to the Speed

What makes overheight strikes expensive is not the impact velocity — these are low-speed collisions — but what gets hit.

• Gantries and height bars — structural repairs, lane closure, and a barrier that is missing while it waits for parts.
• Overhead services — cable trays, pipework, sprinkler mains and busbars running across a yard entrance or a loading canopy.
• Building fabric — roller-shutter headers, canopy edges, and dock leveller housings.
• The load itself — a container or palletised load damaged at the top often means a rejected delivery and a claim, not just a dent.

Then there is the part that never appears on a repair invoice: a lane closed during a peak window, and the appointment slots that get missed while it is closed.

How Height Gets Estimated From Video

A camera cannot measure height directly; it measures pixels and infers. Three inputs make that inference accurate enough to act on.

1. Ground plane calibration. The system is told where the road surface is in the frame. Every height measurement is relative to that plane, so this is the single most important commissioning step.
2. Vehicle detection and classification. A clean bounding box from vehicle detection gives the top and bottom of the vehicle; knowing the class refines the expected geometry.
3. A known reference scale. Lane markings, a painted post, or a measured object in frame converts pixels to metres. Where sites can install a physical marker of known height, accuracy improves substantially.

The output is an estimated height against a threshold you set, with a tolerance band. Set the threshold slightly below the true clearance — if the gantry is 4.2 metres, alert at 4.0 — so measurement noise never results in a missed warning.

Detection runs on the edge device, which handles 2–128 channels and 1–256 TOPS and ships with the full library of 198+ algorithms. That matters here because the approach lane camera is usually worth more than the height check alone.

What to Do With the Alert

An alert nobody receives prevents nothing. The configurations that work are:

• Driver warning — a variable message sign or audible warning before the constraint, so a driver who misjudged can stop or divert.
• Barrier interlock — hold the gate or the shutter closed while an overheight vehicle is in the approach zone, rather than letting it strike.
• Plate capture and logging — bind the event to a vehicle identity via plate recognition, which is what turns a near-miss into a coaching conversation with a carrier and a record for a repeat offender.
• Control-room notification — for unmanned sites, so staff can talk the driver down over an intercom.

The same approach camera can also carry wrong-way detection and speeding detection, which is usually what justifies the installation cost in the first place.

Where It Is Used

Car parks and underground entries with low headroom. Warehouse and DC loading canopies. Weighbridges and terminal gates. Tunnel and bridge approaches. Industrial yards with overhead pipework. Fuel depots and tanker lanes. Toll plazas with height-restricted lanes. In each case the pattern is the same: a fixed, known clearance and a stream of vehicles whose drivers are guessing.

We walk through the reasoning in smart parking system cost.

FAQ

How much over the limit counts as a violation? You set it, and you should set it below the true clearance. If the physical limit is 4.2 metres, configure the alert threshold at 4.0 so that measurement variation and suspension movement never produce a missed detection. The gap between the threshold and the structure is your safety margin.

Can it measure the actual height, or just pass or fail? It estimates an actual height, which is more useful operationally — it lets you see how close vehicles are running to the limit, and whether a near-miss population is growing before a strike happens. Treat it as a well-calibrated estimate rather than a certified measurement.

Do we need to install new cameras? Usually no; the analytics consume your existing streams from an edge box, so cameras and cabling stay. The one thing to check is the viewing angle — a camera too close to the constraint sees the vehicle at a steep angle and measures poorly. Because inference is on-device, it keeps working with no internet connection.

What does it cost? A one-time hardware purchase sized by channels and compute, with no per-camera monthly fee, so adding an approach lane later does not add a recurring charge. Most sites confirm accuracy on their own footage with a Starter Kit before ordering.

Tell Us Your Scenario. Tell us the clearance and the approach layout, and we will recommend camera positions and a threshold. Validate on your own lane with a Starter Kit, or contact us with a site drawing.