DENVER (KDVR) — The summer months are historically the worst times on Colorado roads when it comes to people getting behind the wheel and getting into crashes, according to Colorado State Patrol.

CSP investigated 1,750 fatal crashes and crashes that caused injury over a three-year span from 2019 to 2021 that involved impaired drivers. The top month for these crashes is July.

According to the Colorado Department of Transportation, there has been a 44% increase in the number of deadly crashes involving impaired drivers since 2019.

Colorado State Patrol said these are the top-five counties where these crashes happened in 2021:

  1. Jefferson County
  2. Weld County
  3. Adams County
  4. Larimer County
  5. El Paso County

Another troubling trend on Colorado roads is people driving under the influence of more than one substance, or poly-impaired driving.

2021 was the deadliest year on Colorado roads since 2002, with 691 deaths. Fatal crashes have gone up 50% since 2011 and one in three traffic fatalities involved an impaired driver this past year, according to CDOT.

When analyzing poly-impaired driving, researchers found a combination of alcohol and marijuana was the most common, followed by alcohol and other drugs including cocaine, methamphetamines or opioids.