Overview. If you frequently experience shortness of breath or you hear a whistling or wheezy sound in your chest when you breathe, you may have asthma â a chronic condition that causes inflammation and narrowing of the bronchial tubes, the passageways that allow air to enter and leave the lungs.
1 At 47,958 kilometres (29,800 miles) in total length, the Pan-American Highway is the longest road in the world.  The road starts in Alaska, North America and ends in the lower reaches of South America.
U.S. Route 20 (US 20) is an eastâwest United States highway. The 0 in its route number indicates that US 20 is a coast-to-coast route. Spanning 3,365 miles (5,415 km), it is the longest road in the United States, and the route roughly parallels that of Interstate 90 (I-90). There is a discontinuity in the official designation of US 20 through Yellowstone National Park, with unnumbered roads used to traverse the park. It and US 30 break the general U.S. Route numbering rules in Oregon, since US 30 actually starts north of US 20 and runs parallel to the north throughout the state.