Optimal Design Of Guardrail For The Black Spot In Highway

As today’s society has entered a new time of high speed and efficiency, the construction and operation of highway has been becoming focus of all the fields in the society. The construction state of highway could reflect the degree of traffic and economy development. Compared with the ordinary road, highway is designed for automobile only, fully enclosed with fence and separated by median divider. However, due to the closure of highway and vehicle driving fast, the proportion of serious accident occurred in highway is higher than that in ordinary road. Heavy vehicles make up most of the serious accident. Because of the large weight and high location of gravity center, the heavy vehicles could not be protected from accident by ordinary guardrail very well. If there are not enough protective measures at the black spot of highway, the serious accidents usually lead to casualties.The roadside guardrail is the facilities of "afterthought" for improving traffic safety. The roadside guardrail is divided into3categories:rigid guardrail, semi-rigid guardrail, flexible guardrail. In China the semi-rigid guardrail is commonly used because of the good performance of energy absorption and strength. The semi-rigid guardrail’s main structures are:barrier post, w-beam, prevention block. The ordinary guardrail of split type in median divider is weaken in collision strength, so that it is more likely for vehicle to cross the median divider to the opposite lane once the accident occurred. Moreover, the height of guardrail is designed mainly for protecting mid-scale vehicle and car, and the heavy vehicle is considered inadequately.As investigations show, roadside accident accounted for about one-third of all the highway traffic accidents. There are3mainly forms of roadside accident.1. Getting under the guardrail, most of the accident vehicles are cars which have lower gravity and higher speed.2. Crossing the guardrail, large-scale and mid-scale vehicle that chassis is higher usually encountered this state.3. Rollover from the guardrail, most of the accident vehicles are large-scale trucks and buses.Focusing on the problem of black spot in highway and common situation of highway roadside accident, an improved design for highway guardrail is carried out. The detail size and structure of new guardrail is determined by integrated design method. This design is in order to ensure the protection of small-scale vehicle, while also to protect heavy vehicle from rolling and crossing the guardrail.