Short answer: No day of week or time of day is immune — the peaks are at the end of the night on Fridays, Saturdays, and Sundays, and during the Wednesday and Friday afternoon commutes

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We analyzed 2,600 traffic collisions reported in West Hollywood over the last three years (2015 through 2017). That’s 2.4 collisions per day. The data comes from the California Highway Patrol (CHP), which collects the information from local agencies such as the Sheriff’s Department.

We know drivers don’t report every collision, but we don’t know how many go unreported. We assume collisions involving injuries are more likely to be reported, so property-damage-only collisions may be underrepresented in the following numbers.


Number and severity of collisions

The number of reported collisions has declined in the past three years. There were over 1,000 in 2015, about 800 in 2016, and something more than 700 in 2017. The 2017 total, in particular, may rise as more reports reach the CHP.

Notes: (1) We omitted the 2013 and 2014 totals because they’re clearly incomplete. (2) The numbers prior to 2013 were downloaded in February, 2017. (3) The recent numbers were downloaded on February 17, 2018. Sources: California Highway Patrol, Statewide Integrated Traffic Records System (SWITRS); our analysis

The severity of collisions ranges from fatal to property-damage-only (PDO). We believe there were at least six fatal collisions in the last three years. That was a fraction of a percent of total reported collisions. Together, fatal and severe-injury collisions represented 2% of collisions. The injuries were visible-but-not-severe in 6% of collisions. In 21%, someone complained of pain but there were no visible injuries. The remaining 71% of collisions were PDO.

Note: The CHP data includes four fatal collisions. We know of two others from press reports that haven’t made it into the database yet. Sources: Same as above.


Collisions by month

Based on three years of data, the months of June and October have the most collisions. December has the least.

Sources: Same as above.


Collisions by day of week

There are two to three traffic collisions per day on average, depending on the day of the week. Friday — including the early morning hours of Saturday — is the biggest day. An average of 2.8 collisions were reported each Friday over the three-year period. Saturday was in second place with 2.5 collisions per day. Monday had the fewest collisions: 2.1 per day. In percentage terms, 13% of accidents happened on Mondays and 17% on Fridays.

Note: For this chart, the day starts at 4:00 AM and runs through 3:00 AM the next day. The collision times are rounded to the nearest hour. Sources: Same as above.


Collisions by time of day

Looking only at time of day, the collision peak is around 5:00 PM. About 6% of collisions occur in that hour, as well as the 3:00 PM and 6:00 PM hours. We don’t know why the 4:00 PM hour appears to be a bit lower. There are somewhat smaller peaks at 11:00 PM and 2:00 AM. By comparison, fewer accidents happen in the morning and lunchtime hours.

Note: The collision times are rounded to the nearest hour. Sources: Same as above.


Collisions by time of week

The time-of-day pattern varies by day of week. The collisions associated with the PM work commute happen Monday through Friday. The late-night collisions associated with nightlife occur on the weekend. Friday has both, so it has the highest number of collisions.

Sources: Same as above.

The chart above shows the share of collisions by time of week. The five highest hours are:

  • 2:00 AM Saturday and Sunday, which we think of as the end of Friday and Saturday nights
  • 11:00 PM Sunday
  • 5:00 PM Wednesday and Friday


Relative risk of a collision

The times with more collisions may be higher risk or they may just have higher traffic volumes. We can’t do a full analysis, because we don’t have hour-by-hour citywide traffic volume data. However, we have enough data to estimate the relative collision risk by time of day on Santa Monica Boulevard on Tuesdays and Wednesdays. The numbers are relative to the risk for the day as a whole, which is set at 1.0.

Note: Based on vehicle counts rather than vehicle-miles, because that’s the hourly data we have. Sources: SWITRS; Caltrans; our analysis.

The estimates suggest that the hours between midnight and 2:00 AM are roughly three times riskier than most of the rest of the day. The safest time is 6:00 in the morning. The afternoon commute is a bit riskier, but most of the extra collisions in those hours are due to higher traffic volumes.


Collision severity by time of day

The six fatal collisions we know about from this period all occurred between 11:00 PM and 5:00 AM. Non-fatal injury collisions were spread more proportionately through the day and night.


http://wehobythenumbers.com/wp-content/uploads/2018/02/201803-collisions-time-of-week.jpghttp://wehobythenumbers.com/wp-content/uploads/2018/02/201803-collisions-time-of-week-300x300.jpgDavid WarrenPerformance (effectiveness)Public safetyTransportationdriving,streets,traffic
Short answer: No day of week or time of day is immune -- the peaks are at the end of the night on Fridays, Saturdays, and Sundays, and during the Wednesday and Friday afternoon commutes| We analyzed 2,600 traffic collisions reported in West Hollywood over the last three years...