As summer travel ramps up, safety experts are warning drivers about the return of the “100 Deadliest Days” — the stretch between Memorial Day and Labor Day when roadway accidents traditionally increase across the United States.

New findings from Mercury Insurance reveal that certain times of day are significantly more dangerous for drivers in California. The company analyzed five years of accident claim records to pinpoint the exact 10-minute periods when crashes happen most frequently.

The study found that, statewide, the riskiest time to be on the road in California is between 12:00 p.m. and 12:10 p.m. However, the peak danger period varies by county.

For example, in both Los Angeles County and San Bernardino County, crash activity is highest between 3:00 p.m. and 3:10 p.m.

• Highest-Risk Driving Windows by County

• Alameda County: 12:00 p.m. – 12:10 p.m.

• Contra Costa County: 2:00 p.m. – 2:10 p.m.

• Fresno County: 3:00 p.m. – 3:10 p.m.

• Los Angeles County: 3:00 p.m. – 3:10 p.m.

• Orange County: 12:00 p.m. – 12:10 p.m.

• Riverside County: 12:00 p.m. – 12:10 p.m.

• Sacramento County: 4:00 p.m. – 4:10 p.m.

• San Bernardino County: 3:00 p.m. – 3:10 p.m.

• San Diego County: 12:00 p.m. – 12:10 p.m.

• Santa Clara County: 4:00 p.m. – 4:10 p.m.

Across the country, weekdays tend to see the most crashes during the 3:00 p.m. hour, especially in the first 10 minutes after the hour. Mercury Insurance also noted that injury severity tends to increase later in the afternoon, particularly between 4:00 p.m. and 4:10 p.m., when traffic speeds increase.

During the busiest 10-minute weekday period, more than 61,000 people were involved in accidents over the five-year study period.

Interestingly, the research challenges the idea that traditional rush hour is always the most dangerous time to drive.

Heather Paull, divisional claims manager at Mercury Insurance, explained that in the early afternoon, traffic often becomes congested due to school dismissals and commuters entering the roads. These conditions usually lead to lower-speed collisions and stop-and-go accidents.

According to Paull, crashes later in the day tend to be more serious because traffic flows more freely and drivers may become less attentive or begin speeding.

Weekend driving patterns look different. Instead of late-afternoon congestion, crash activity peaks around noon as people head out for errands, shopping, dining, and leisure activities.

Nationwide, roughly 19,000 people were involved in crashes during the highest-risk weekend 10-minute period, and nearly 9% of those incidents resulted in injuries.

Pedestrians Face Even Greater Risks

The data also highlighted the dangers for pedestrians. Injury rates in pedestrian-related accidents often exceed 60%, and in some situations can climb above 80%.

The highest-risk periods for pedestrians typically occur:

Around lunchtime

During commuting hours

In the middle of the afternoon

Even incidents involving fewer vehicles frequently lead to severe injuries when pedestrians are involved.

Mercury Insurance says traffic danger follows predictable daily patterns rather than occurring randomly. Weekday risks are largely linked to school pick-ups and evening commutes, while weekends are influenced by concentrated midday travel.

The company advises drivers to remain patient during busy afternoon hours, maintain safe following distances, minimize distractions, and stay alert as traffic conditions change throughout the day.

For travelers planning a California road trip this summer, understanding when roads are most dangerous could help make journeys safer and less stressful.

You can read Mercury Insurance’s full analysis here.