Vowel whose quality does not change over the duration of the vowel is called a monophthong. Monophthongs are sometimes called "pure" or "stable" vowels. A vowel sound that glides from one quality to another is called a diphthong, and a vowel sound that glides successively through three qualities is a triphthong. All languages have monophthongs and many languages have diphthongs, but triphthongs or vowel sounds with even more target qualities are relatively rare cross-linguistically. English has all three types: the vowel sound in "hit" is a monophthong , the vowel sound in "boy" is in most dialects a diphthong , and
Road collision types is often significantly worse because of the increased speeds involved. Because intersection collisions often result in side-impacts they are therefore often fatal because people are seated close to the part of the car that provides little protection. Although expensive to implement, roundabouts are an effective way of reducing the speed of traffic at intersections and dramatically reducing the likelihood of high speed right-angle collisions. Clear road markings and signing are low cost methods of improving safety at intersections. Road collision types Road traffic collisions generally fall into one of four common types: Other types of collision may occur. Rollovers are