WOODBURY - Officials say gas is being pumped into the city subways this week as part of a terrorism research test being carried out by Brookhaven National Laboratory.

Subway riders have been seeing the alerts about the tests recently.

At 8 a.m., Brookhaven researchers and the NYPD released harmless gas in the subway tunnels to track how gas spreads in all five boroughs.

Data from the $3.4 million federal study will help first responders develop emergency tactics.