The Ups and Downs of Parking Lot Control Arms

My office is contacted many times a month regarding a parking lot control arm or barrier gate injury of some sort. These terms are generally interchangeable; however, some standards do not use the term control arm, only barrier arm. Usually, the attorney starts by explaining that the plaintiff was hit by a descending parking lot arm without any advance warning. Sometimes the injured party is riding a motorcycle, sometimes walking as a pedestrian under the arm. In other claims the gate arm does not fully cycle open before returning to the horizontal position. There are also cases where the gate appears to have been left in an open position, turned off, and is remaining in the upright position for extended periods of time and suddenly descends just as a pedestrian begins to pass under it. There are numerous variations of the same type of accident, but there are big differences in who the responsible party is for the cause of injury. Some of the first questions asked pertain to how the device works, and why the arm did not detect the person as they walked through the driveway.

FULLY AUTOMATED OR ATTENDED, BOTH SHARE SOME CHARACTERISTICS


Manufacturers of most barrier arm gates build their devices to activate in one of two different ways. Fully automated by remote stimulus and/or manually controlled by a parking lot attendant.


Many parking lot control arms are activated when a driver pulls up to a parking lot gate in a vehicle. As the vehicle arrives, an electronic signal is sent to the arm mechanism due to the detection of that vehicles large metallic presence interacting with an in-ground magnetic field. This


in- ground magnetic field is created from buried wires known in the trade as an induction loop. The signal generated from this "activation or approach magnetic induction flux loop" often is connected to a ticket printing device. This piece of equipment is commonly referred to as a "Ticket Spitter". The "Spitter" issues a ticket, usually for single vehicle access prior to activating the barrier arm gate mechanism causing the arm to raise. An alternative method to get the control arm raised requires a driver to reach out of the car and push a button to receive a parking lot access ticket from the "Spitter". (In that mode of operation, it is probable that there is no magnetic loop in place.) In either case, once the ticket is taken by the driver, the "Spitter" sends a control signal to the gate arm mechanism, and the arm is supposed to raise, generally for a single vehicle to control access to the parking lot.


As the vehicle transitions from the approach location where the ticket is issued, once the control arm raises, there is usually a functioning magnetic flux or induction "Safety Loop" located under the control arm swing location which provides protection for a vehicle until it has cleared the "Zone of Danger" underneath the active arm. The control arm may also be kept in the open position by a timer that holds the gate arm up for a predetermined time prior to closing. Using a timer function in place of an in-ground magnetic loop is risky, as vehicles may not clear the opening, or another vehicle can attempt to gain access without receiving a usage ticket. Older, non-current standard compliant installations have been seen without any consistency of design or operational function.


There are multiple installation variables that can alter the basic loop positions and quantities, but most basic systems operate as described above using at least two control loops. One underneath the control arm, and one egress or approach loop. In some installations, all three loops will be present. This triple looped system offers the most comprehensive safety for a vehicle, NOT A PEDESTRIAN!


MANUAL VERSIONS OF PARKING LOT CONTROL ARMS


A parking lot attendant, usually positioned inside an adjacent booth, has a control switch that activates the parking arm. The attendant has a switch that raises the arm, lowers the arm, and keeps the arm inactive, either up or down. Some manually controlled arms also have magnetic induction loops connected to the parking lot control arm when the parking lot is unmanned after hours, in which case, the arm should function in the fully automatic mode, as described above.


BARRIER ARMS ARE WEIGHT ACTIVATED, RIGHT?


Contrary to popular belief, most are activated due to a change in a magnetic field which is generated by twisted energized wires positioned below the adjacent pavement of the control arm. Modern arms are not usually controlled by pneumatic pressure like an old-fashioned gas station bell hose. It is unlikely that the weight of a vehicle or a pedestrian walking underneath the arm will stop an active arm. Modern parking arms are triggered by a change in the magnetic induction loop return. Modern induction loops are manufactured from a relatively light gauge of wire, placed in a rectangular shape that is calibrated and sized to detect a change in the magnetic field when a metallic object such as a vehicle enters or covers that field.


Many attorneys insist to me during their initial call that a pedestrian walked next one and activated the arm due to their client's weight, and the arm failed to remain open as they walked under the arm. This scenario is generally incorrect. Weight of a vehicle, or weight of a pedestrian cannot activate most modern parking control arms. A trigger of an arm or activation of a street traffic light due to weight has not been in practice for many years. It is highly unlikely that a pressure pad sensitive to weight is ever controlling a parking lot arm today.

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