The Honda Civic 4-door, Hyundai Sonata, Lexus RX and Nissan Altima are the latest vehicles to earn the top award from the Insurance Institute for Highway Safety.

The four vehicle models join the 2016 winner's circle, just one month after IIHS announced the initial crop of 48 Top Safety Pick+ winners.

For this year, IIHS tightened the requirements for Top Safety Pick+. To qualify, winners must earn “good” ratings in each of the institute’s five crashworthiness tests and have an available front crash prevention system earning an “advanced” or “superior” rating.

Vehicles that meet the crashworthiness criteria but have only a “basic”-rated front crash prevention system qualify for the second-tier award, Top Safety Pick.

The Civic, Sonata, RX and Altima all come with “superior”-rated optional front crash prevention systems. In IIHS track tests, the first three vehicles avoided collisions at 12 mph and 25 mph, according to IIHS. The Altima avoided a collision at 12 mph, while in the 25 mph test its impact speed was cut by 10 mph. All four systems include a warning function that meets National Highway Traffic Safety Administration criteria.

The Civic 4-door, a small car, and the RX, a mid-size luxury SUV, both received design makeovers for 2016. The 2015 Civic had qualified for Top Safety Pick under the old criteria, while the previous generation of the RX had never been tested in the challenging small overlap front crash, IIHS noted.

The Sonata and the Altima, both mid-size cars, were 2015 award winners. Both cars had their structure improved to raise their small overlap front ratings from “acceptable” to “good.”

Previously, vehicles could qualify for Top Safety Pick or Top Safety Pick+ with an “acceptable” rating in the small overlap front test.

In the case of the Sonata, the improvements were made after production for the 2016 model year had already begun. The award only applies to Sonatas built after October, IIHS said. A vehicle’s manufacture date is indicated on the certification label, typically located on or near the driver door.