The issue was discussed this month on the Wairarapa Commuters Facebook page, on which Peter Jackson posted, "so what's the deal with these flashing lights on the hill that are supposed to indicate that an approaching truck is just around a sharp corner?
"In my view, they don't work too well, having just about been taken out by a semi halfway into my lane this evening," he wrote. "Not a flash."
Meanwhile, Josh Coe said he had "met a number of trucks with no warning" along the stretch of road.
Mr Owen said the agency was monitoring the system and making adjustments as necessary. "The timing of when a large vehicle is detected and the signs starting to flash or the length of time they flash are two of the things we are tracking and, as necessary, adjusting."