You can achieve this via two triggers wired to constantly trigger each other, each broadcasting on a different channel. Make half the barriers have settings to deactivate on channel a and activate on channel b, and half the barriers have settings to activate on channel a and deactivate on channel b. After setting that up, place down two triggers, and wire them to each other. The wire setting should be when triggered----trigger. Set the trigger delay to whatever you want, this will be the time each barrier stays active. (aoms uses 3 seconds if I remember correctly). Now make the first trigger transmit on channel a when triggered, and the second trigger transmit on channel b. Lastly, you need something to kickstart the switching. So place down a lifecycle and wire it to the first trigger. That, in theory should make alternating barriers.