Reliability-based design for highway horizontal curves

• Main Author: Felipe, Emmanuel Leon
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/4497

For more than fifty years the notion of comfortable lateral acceleration has governed the horizontal curve design procedure in North America. With new road and vehicle technology, new methods of design have to replace the old procedures to provide consistent and safer roads to the users. The "limit state design" concept, taken from structural engineering, has already shown to provide a meaningful value of safety to highway design, see Navin (1990-1992). With the cooperation of the British Columbia Ministry of Transportation and Highways, controlled experiment and field observation were performed to develop the "limit state design" concept for highway horizontal curves. These measurements allowed to accumulate actual statistical information of the basic variables involved in the driving process of horizontal curves. During the experiment, designed with a Latin Square, eight regular drivers and two expert drivers drove four different curves at two speed levels and two pavement conditions. The response variables from this experiment were the lateral acceleration, the speed and the level of comfort. During the observation, in addition to the geometric characteristics of the four horizontal curves selected on the "Sea to Sky" Highway, the speed, lateral acceleration and lateral placement of the free moving passenger cars traveling through these curves were gathered. The computer program RELAN was used to perform First Order Reliability Method (FORM) analysis for passenger cars subjected to skidding by comparing the expected lateral acceleration supplied by the road to the expected lateral acceleration demanded by the vehicle-driver. RELAN was also used to compute the reliability index P and to provide the probability of noncompliance for existing highway horizontal curves, by comparing the expected radius supplied by the highway to the expected radius demanded by the car/driver system. From data collected during the empirical studies^ results show an increased probability of non-compliance with a decrease of radius. Using reliability-based design method, transportation engineers can adjust the design of horizontal curves to fulfill a desirable probability of non-compliance or a desirable reliability index (3. Designers have also a representation of the main variables involved in the process of driving in a horizontal curve and, therefore, have a better control of their designs. With reliability analysis, transportation engineering is provided with a highway design method which better responds to the actual driving demand on the road, and is supported with a measure of 'safety' or non-compliance.