Number plate recognition for access control: how it works and what it needs
Quick answer
A dedicated camera photographs the vehicle, software extracts the plate and compares it with a list of authorised vehicles; if it matches, the barrier or gate opens. It works well if the camera is correctly positioned and the vehicle passes slowly, but it is never one hundred per cent accurate: there must always be a fallback way to open.
How it works, step by step
- Detection. An induction loop in the ground, or image analysis itself, detects an approaching vehicle.
- Capture. A camera with infrared lighting and a fast shutter takes the image, day and night.
- Recognition. Software finds the plate and converts the image to text. This is ANPR (or LPR).
- Decision. The plate is compared with the authorised list, including schedule and expiry.
- Action. The barrier opens and the passage is logged, usually with the photo.
What reliability depends on
- Angle. The more head-on, the better. Steep horizontal or vertical angles distort the characters.
- Distance and framing. The plate must cover enough pixels; each camera has its range.
- Speed. A lane that forces drivers to slow (speed bump, turn) improves reading.
- Light. Infrared handles the night; oncoming headlights and low sun are the challenge.
- Plate condition. Dirt, tow bars, damaged or obscured plates.
- Quality of the recognition engine and its support for the plate formats you receive — relevant if many vehicles are UK- or other foreign-registered.
Be wary of anyone promising one hundred per cent. Ask for a trial at your own entrance.
Installation requirements
- A defined lane: vehicles must always pass the same point.
- A solid mount for the camera, at the height and distance the manufacturer specifies.
- Power and network at that point.
- A barrier or gate with an opening-command input (types of barrier).
- Safety devices on the automation in good order.
Plan B
Sooner or later a plate will not read. Provide at least one of: card or remote, opening from a phone, intercom answered remotely, or keypad.
Is it secure as the only credential?
A number plate is visible to anyone and can be copied. For a company or residential car park it is usually a reasonable compromise; for sensitive sites, combine it with a second factor (a long-range card, for example).
Data protection
A plate linked to a keeper is personal data.
- Inform with a sign at the entrance.
- Limit retention of photos and logs.
- Restrict who can view the history.
- Do not record the public street beyond what is essential.
- In residential communities, an owners' meeting agreement (community garages).
More in CCTV and access control.
Day-to-day management
- Adding and removing plates: who does it, and how?
- Courtesy and hire cars.
- Visitors: temporary authorisations with an end date.
- Suppliers: lists by schedule.
When it is not the best option
- Entrances where vehicles arrive at an angle or fast and that cannot be changed.
- Fleets that change vehicles constantly.
- When a registered remote is enough and you would rather not process plates.
We survey the camera position and run the trial at your entrance as part of our parking access control service.
Frequently asked questions
Does it work at night and in the rain?
Yes, dedicated cameras use infrared lighting. Heavy rain, fog or a very dirty plate reduce the hit rate, hence the need for a fallback.
Will an ordinary CCTV camera do?
In very favourable conditions it may read some plates, but it is not reliable. ANPR cameras have optics, shutter and lighting designed for the job.
This guide is for information only and is not a substitute for legal advice or for the technical design of each installation. Regulations change: always check the current text at the official source.