RALEIGH, N.C. (WAVY) — The North Carolina Department of Transportation (NCDOT) announced on Friday afternoon that they will once again temporarily lower the speed limit on William B. Umstead Bridge.

The change, effective immediately, will lower the speed limit from 55 mph to 20 mph each day at dusk and dawn. Officials say flashing lights will activate each morning and night to alert drivers of the change.

Each summer, from July to August, as many as 100,000 purple martins call the west end of the bridge home before they migrate to Brazil. At times, the flock is so large it can be seen on radar.

The birds will roost under the bridge each night before they leave in the morning to go feed. They return each night around sunset.

NCDOT officials say motorists can also take the Virginia Dare Memorial Bridge as an alternative