Boom Gate Arm Length Guide: Matching Barrier Length to Lane Width

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The boom arm should be long enough to span the full lane width when raised to the vertical position, leaving clearance on both sides for vehicles and mirrors. Measure the actual lane width at the barrier location, not the drawing width, and allow for the post position, the arm's closed rest position and any barrier housing. Exact values depend on your site and vehicle mix, so confirm the final length with the manufacturer's engineer before ordering.

Why lane width drives arm length

The boom arm of a parking barrier has to cross the lane when it is lowered and clear the lane when it is raised. In practice, the arm length is chosen so that the closed arm reaches the far edge of the lane, while the open arm sits upright beside the housing without blocking traffic. Lane width is therefore the main input, but it is not the only one.

Start by understanding what the barrier needs to do on your site, whether it controls one entry, an exit or a shared lane.

Measuring the lane correctly

Measure on site, not from plans alone. Record the clear width between curbs or painted lines at the exact point where the barrier will sit, and measure again at a second point to check consistency.

Clear lane width between the kerbs or lines at the barrier post
Height of the pedestrian and vehicle approach, if the barrier sits on a slope
Position of the barrier post relative to the lane centre
Any islands, bollards or signs that the arm must clear

Adding clearance for vehicles and mirrors

A simple span measurement is not enough. Vehicles drive with mirrors extended, and drivers rarely stop exactly in the centre of the lane. A practical approach is to allow additional clearance on both sides of the arm so that the barrier is not struck by wing mirrors or roof racks.

Consider the typical vehicles using the site, including vans and delivery trucks, since they set the minimum height and width the lane must accommodate.

Balancing arm length with the drive mechanism

A longer arm carries more weight and puts greater load on the motor, bearings and mounting. Longer arms also take longer to raise and lower, which affects throughput at busy entrances. For this reason, arm length is usually chosen together with the drive unit, the counterbalance and the duty cycle the site requires.

Very long arms may need extra support or a different profile to stay stable in wind, so the choice of length and arm construction should be decided together.

Site conditions that change the answer

Several site factors can shift the right length. Slopes and uneven ground change the arm's height over the lane. Exposure to wind, heavy rain and salt air affects materials and finishing. Traffic speed and the presence of pedestrians also matter, because they influence how the barrier should respond to an obstruction.

Gradients at the entry point
Exposure to wind and weather
Mix of cars, vans and trucks
Pedestrian crossing near the barrier

Confirming the final length before ordering

Once you have your measurements, prepare a short written brief with photos, a sketch and the vehicle types. A site visit by the supplier's technician is the most reliable way to confirm the arm length, post position and clearances. Ask for the arm length to be stated in the specification you approve, so the installed unit matches your requirement.

For any safety-related figure, check the requirements with your engineer and the relevant standards rather than relying on general rules of thumb.

Frequently asked questions

Should the arm exactly match the lane width?

No. The arm should reach the far side of the lane with some allowance, so that vehicle mirrors and small misalignments do not strike it. Confirm the final figure with the supplier after a site visit.

Can I use the drawing width instead of measuring on site?

It is better to measure on site at the barrier position. Drawings often differ from the built lane because of kerbs, finishes and tolerances.

Does a longer arm always need a stronger motor?

Usually yes, because the weight and wind load increase with length. The drive unit and counterbalance should be selected together with the arm.

Who should confirm the final arm length?

The supplier's technician, together with your engineer, should confirm the length after reviewing the site, the vehicle mix and the safety requirements.

Common mistakes to avoid

The most common mistakes are measuring the lane from drawings instead of on site and leaving no clearance for mirrors. Ignoring slopes, wind exposure and the drive unit can also lead to a barrier that works poorly in practice.

Our recommendation

Measure the clear lane at the exact barrier position, add clearance for the largest vehicle that uses the lane, and have the final length confirmed with the drive unit in mind before ordering.

Summary

Match the arm length to the measured clear lane width with added clearance, then confirm the final figure on site with the supplier and your engineer.

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