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SACRAMENTO, Calif. (KTXL) — Wrong-way crashes are a problem so serious that Caltrans and the California Highway Patrol have been making changes for several years to warn drivers.

Some of the harder-to-miss changes are signs warning drivers to not enter, but these crashes continue to happen. 

On Tuesday morning, a BMW slammed into a big rig, shutting down every lane of traffic on southbound Interstate 5 just ahead of the Interstate 80 connector. The CHP said a 28-year-old Sacramento man was driving in the wrong direction, allegedly drunk, when he hit an 18-wheeler head-on. 

The crash injured two people inside the big rig. 

It is not yet clear how long the driver was heading in the wrong direction or where he entered the freeway. Those are important pieces of information as Caltrans is concerned. 

“Some of the on and off-ramps also have larger signs and they may be flashing at some point. And some of them also have sensors and cameras,” Dennis Keaton, with Caltrans, said. 

Those sensors are triggered when a driver enters in the wrong direction, giving officers a license plate and car to search for on the freeway. It is also now policy that all freeway ramps have clear reflectors that drivers will see when traveling in the correct direction. 

“But if you’re coming from the opposite direction, you’re seeing red reflectors,” Keaton told FOX40. 

Those measures are the result of a three-year pilot program by Caltrans and UC Davis aimed at reducing wrong-way crashes. The safety effort was prompted by 10 such accidents that happened in the first half of 2015 in the Sacramento and San Diego areas. 

Though Caltrans said they continue to study how to make it harder to drive in the wrong direction, there is only so much they can do. 

“The study showing that the preventative measure needs to be drivers need to not be behind the wheel if they’re impaired in any way,” Keaton said. 

Everyone involved in the crash Tuesday morning survived. On average, 37 people die in wrong-way crashes on California freeways, according to the CHP. 

Caltrans measures have been effective. Numbers show a slight decrease in the percentage of crashes since the beginning of the program. Specifically, Caltrans reports wrong-way crashes in San Diego were down 44% after installing reflectors.