These lights, which will operate round the clock, have been installed at the site to allow Welsh Water workmen to carry out work at the site as part of the construction of the Rotherwas access road.
An overbridge is being constructed to take the Hoarwithy road over the new road.
The lights are expected to be in place for about a week.
Motorists who use this road are being advised to leave extra time for their journey.
Letters are being sent to residents living nearby to make sure they are aware of the situation.