A police officer typically requires that a suspected drunk driver undergo a field sobriety test to confirm impairment before a breath test can be administered. The permissible drink drive limit across the United States is high - 80 milligrams of alcohol per 100 millilitres of blood - and well above the 50 milligram limit prescribed in most countries. The legal constraints applicable in the United States do not allow best practice enforcement to be carried out, and high rates of alcohol related road trauma continue.