Traffic fatalities claimed about 35,000 Americans in 2015, so vehicle safety is serious business. But a lot of high-tech safety options are expensive, and some don’t work as well as you might think. Here’s one feature we think is worth ponying up the cash for, and one that we haven’t seen quite as much benefit from.

The feature that’s unquestionably worth the money is forward collision warning with automatic emergency braking. These systems use cameras and other sensors to scan the road in front of you for objects you’re rapidly closing in on. They can alert you with chimes or vibrations and, if you don’t do anything, hit the brakes to avoid a collision or at least lessen it. In an age of distracted driving, this is crucial. The National Transportation Safety Board reports that almost half of two-car crashes from 2012 to 2014 were rear-end collisions. This feature can reduce them.

At the other end are lane-departure mitigation systems. In our experience, these systems exhibit a lot of inconsistencies depending on light and water conditions – and that assumes proper lane markings in the first place. Many of them now employ assistive steering or brakes to keep you in your lane, but short of true lane-centering steering system, these can be inconsistent. Most of them time out in a few seconds if you don’t touch the wheel, and their reactions range from almost nothing to sudden, unexpected jerking. We understand why these features work only briefly, but we question the logic behind any active safety system that works only part of the time, regardless of why.