American law follows the basic idea that most people are reasonable and laws exist to control the few who are unreasonable or inconsiderate. All roadways in Oregon have specific speed limits.
Speed limits do not authorize speeds higher than those required for compliance with the basic speed rule.
How does ODOT determine the speed limits?
Designated speed limits must be posted to be enforceable, while statutory speed limits may be posted or unposted as determined by the road authority. All designated speeds are established through an engineering investigation.
Previous studies suggest posting speeds near the 85th percentile speed minimize crash occurrence and provide favorable driver compliance. More recent studies suggest that posting near the 50th percentile speed may be more appropriate for roadways within urban areas where there is development and vulnerable users.
The investigation is based upon nationally accepted standards and includes a full review of roadway characteristics and roadside context. These characteristics include, but are not limited to, crash history, traffic volumes, highway geometry, roadside culture and density, and 50th and 85th percentile speed. These are the speed at or below which 50% and 85% of the vehicles are traveling.
What is the basic speed rule?
In addition to speed limits, all travel on public streets and highways is subject to the "basic speed rule" as described under
The basic speed rule states that a motorist must drive at a speed that is reasonable and prudent at all times by considering:
- Other traffic.
- Road and weather conditions.
- Dangers at intersections.
- Any other conditions that affect safety and speed.
In other words, drivers are expected to use good judgment in selecting their speed. What this means is a person can also drive below the posted speed and violate the basic speed rule. For instance, if there is ice or snow on the roadway, a driver can be traveling less than the speed limit posted and still be traveling faster than is reasonable and prudent for the conditions.