The Chicago Transit Authority is installing surveillance cameras in about 850 rail cars to assist law enforcement, according to a news release.

CTA began last week its seven-month project to retrofit surveillance cameras in older model rail cars on the Red Line, according to the release. Workers will equip every car with an on-board recording device and four 360-degree high definition cameras.

The upgrade will not affect Purple Line trains, as CTA will replace the 2400 series trains running on Purple Line with new 5000 series that have cameras on every car, CTA spokeswoman Catherine Hosinski said. CTA expects to complete the replacement by September, Hosinski said.

The project stems from Chicago Mayor Rahm Emanuel’s effort to improve safety across the CTA, according to the release.

“Having a world-class public transportation system is a key goal of my administration, and making sure that Chicagoans can have a safe experience on board our trains and buses is a top priority,” Emanuel said in the release. “These additional cameras will work directly with the many other upgrades we’ve made to improve the experience of our passengers, so they can get to work and school smoothly and safely.”

Evanston Police have used CTA surveillance camera recordings in the past to solve a robbery case and a murder case on Howard Street, EPD Cmdr. Jay Parrott said.

“They are extremely important, and they’ve proven that,” Parrott said.

Tanner Maxwell contributed reporting.

— Jia You