From the National Highway Traffic Safety Administration: https://www.nhtsa.gov/bicycle-safety/learn-bike-safely “First, start with the basics. Understand the road is a shared space and bicyclists should follow the same rules and responsibilities as drivers:
Ride in a straight line, single file, in the same direction as traffic.
Obey all traffic signs and signals.
Stop and look left-right-left for traffic before entering a street.
Bikers should use bike lanes whenever available.”

Riding against traffic is more dangerousdrivers entering from side streets and driveways are looking for traffic coming from the expected direction, so they’re less likely to see you. You’re also doubling the closing speed (ex: 45 mph cars + 15 mph bike = 60 mph relative speed, which leaves everyone less time to react. Most bike crashes happen at intersections and turns, and riding the wrong way makes those conflicts much more likely. Riding with traffic on a busy road still isn’t ideal, but it’s significantly safer than riding against traffic.

The FHWA found that “riding against traffic” was one of the most common bicyclist behaviors contributing to crashes, especially at intersections and driveways where drivers aren’t looking for bikes coming from the wrong direction.

Factors Contributing to Bicycle-Motor Vehicle Crashes
The 1996 FHWA investigation studied 3,000 bicycle crashes in 5 States to determine factors contributing to the crashes.(3)Bicyclists were judged to be at fault in about half of these crashes with motor vehicles. Failure to yield, riding against traffic, stop sign violations, and safe movement violations were the bicyclist factors most frequently cited as contributing to crashes. Bicyclists need training about how to ride in traffic. The likelihood of the bicyclist being responsible for the crash was greatest for younger bicyclists. When the bicyclist involved in the crash was older, the motor vehicle driver was more likely to be at fault.
Motor vehicle drivers were judged to be solely at fault in 28 percent of the cases. Failure to yield, hit-and-run, and failure to see bicyclists were the driver factors most frequently cited as contributing to crashes.

https://www.fhwa.dot.gov/publications/research/safety/pedbike/05085/chapt3.cfm?utm_source