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).
Any rubber that is covering Lincolnâs face is more than 2/32. Ruler: Using a ruler is also an easy and accurate way to check tread depth. Measure between your tread lines with a ruler and use the 1/16â scale. Just remember that 1/16â is equal to 2/32. Tread Gauge: Purchasing a tread gauge is the best way to measure your tread as this takes the estimation and math out of the process.