SAN controller expressed concern regarding the airport's operation of vehicles on the runway displaced threshold during landing operations; the reporter noting AMASS failed to alarm and briefings regarding same absent.

Narrative

We were advised by Airport Operations that they would be putting construction vehicles on the runway in the displaced threshold. They advised us that they had a waiver for this operation. We advised them that there were still 3 arrivals lined up to land. They said this was pre-coordinated and the aircraft could land still with the vehicles in the displaced threshold. We observed the vehicles move onto the runway. We advised the arrivals of vehicles in the displaced threshold and cleared them to land. As the aircraft crossed the end of the runway we realized that the AMASS was not alerting. The AMASS did not put the vehicles on the runway into safety logic and did not see a conflict. Three aircraft landed over the vehicles. Recommendation: 1. There has been a lot of construction on the airport and no verbal briefings on changes; these should be verbally briefed. There was an informational item that approved vehicles in the runway safety area but nothing specific about being on the runway and is no longer in the binder. 2. AMASS should not be left in operational mode if the safety logic does not work and will not alert.