NEW YORK - The New York City Police Department has boosted police patrols in the subway system especially at night because there's been a drastic increase in robberies on the trains. 

"When we talk about robberies we are talking about the use of force," said NYPD Chief of Transit Edward Delatorre.

So far this year there have been 159 robberies across the city in the subway system, an increase of 17 percent compared to last year during the same time period. 

Delatorre says a big part of that increase in robberies has happened in Manhattan. Now over 100 additional transit officers have been assigned to actually ride the trains from for the entire route and not get off during late night hours. 

"Stay on the same line going through the different boroughs and through the different transit districts.  And those officers are there until about 6 a.m.," Delatorre said.

Police say the uptick in robberies happened from January through March. April robberies were about the same as they were in April of 2017, roughly one robbery a day across the entire system. And many of those committing the crimes have been caught. 

"Of the 159 robberies that we have had in the system year-to-date, we have 123 arrests," Delatorre said. 

Whether it's a robbery or case of groping, police say subway riders have helped out tremendous in making arrests. More and more people are taking pictures and video of their attackers.

And uniform and undercover officers are on the lookout for repeat offenders.

"Half the crimes is taking place on trains and half the crime is taking place on the subway station, the mezzanines, the platforms. So we have to constantly make sure we are looking at deployment," said Police Commissioner James O'Neill 

NYPD statistics show that overall crime in the system has declined about 8 percent this year compared to the last year at the same time.

Police say there are about six to seven crimes on the subway each day with a ridership of six million daily passengers.