The road is now mostly owned and maintained by the state through the Oregon Department of Transportation as the Historic Columbia River Highway No. 100 (still partially marked as U.S. Route 30; see Oregon highways and routes) or the Oregon Parks and Recreation Department as the Historic Columbia River Highway State Trail.
Measuring Tire Tread Depth with a Tire Gauge. While U.S. coins can be used to estimate remaining tread depth as a tire approaches the end of its useful life, the established method of measuring remaining tread depth in the U.S. is with a gauge that reads in 32nds of an inch (other countries measure tread depth in millimeters).
The Penny Test. In the United States, tire tread depth is measured in 32nds of an inch. New tires typically come with 10/32â or 11/32â tread depths, and some truck, SUV and winter tires may have deeper tread depths than other models. The U.S. Department of Transportation recommends replacing tires when they reach 2/32â, and many states legally require tires to be replaced at this depth.