Gate Arms

Select View ➔ Gate Arm menu item

Gate arms are traffic control devices which restrict access to a section of roadway. They are commonly used for on-ramps or reversible lanes.

Setup

The gate arm properties form has setup information.

The verification camera preset can be used to check oncoming traffic before operating gates.

An action plan is required for each gate arm group to be controlled. It must have three phases:

• ga_open: gates open and optional DMS displaying "open" message
• ga_change: gates open, with DMS displaying "closed"
• ga_closed: gates closed and optional DMS displaying "closed"

Device actions must be assigned to these phases to control devices:

• Gate arm hashtags should be assigned to ga_open and ga_change, but not ga_close.
• Different DMS messages can be displayed for each phase, as necessary.

States and Interlocks

Gate arms are continuously monitored, and can be in one of these states:

If communication is lost to a gate arm for longer than the value of gate_arm_alert_timeout_secs system attribute, its state will be set to UNKNOWN.

An interlock can prevent dangerous traffic conflicts:

• Deny Open prevents opening, triggered by opposing gates possibly open or downstream gates possibly closed.
• Deny Close prevents closing, triggered by upstream gates possibly open.
• Deny All prevents opening or closing (both conditions above).
• System Disable prevents operating any gates (see below).

If a constraint is broken, IRIS will never automatically try to resolve it. Instead, an alert will logged in the email_event table.

Control

On the gate arm tab, up to two DMS associated with the selected plan are displayed, with current messages. Also, video from one or two verification cameras is shown. The swap button can switch between larger and smaller views.

Below that, up to 6 associated gate arms are listed, with the current arm state and interlocks for each.

There are three buttons to control the plan, which are enabled dependeing on the current phase. When an operator presses a button, its corresponding phase will be requested:

• Open ⇒ ga_open
• Change ⇒ ga_change †
• Close ⇒ ga_closed

† Change is only enabled if a device action is configured with the ga_change phase. Operators can use this to warn motorists when the gates will soon be changed.

Security

There are a couple of extra security features to restrict access to gate arm control.

Allowlist

There is a list of IP addresses from which clients are allowed to control a gate arm action plan. It is specified as the gate.arm.allowlist property in the /etc/iris/iris-server.properties configuration file. The property contains a list of addresses in CIDR notation (exact IP, or ranges specified such as 192.168.1.0/24).

System Disable

Another security feature causes the entire gate arm system to be disabled whenever a configuration change is made. This includes any changes to a gate arm, controller, associated comm link or action plan. IRIS will not send any command to open or close any gate arm while in this state. The only way to re-enable gate arm control is to create a file in the server filesystem at /var/lib/iris/gate_arm_enable (using the touch command).