Design of Horizontal Curves with Downgrades using Low-Order Vehicle Dynamics Models

Open Access
Author:
Varunjikar, Tejas
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Sean N Brennan, Thesis Advisor
Keywords:
  • horizontal curve design
  • vehicle dynamics
  • friction demand
  • bicycle model
  • CarSim
  • point mass model
  • LuGre tire model
  • tire pavement friction
Abstract:
Geometric design of highways is an important aspect of highway engineering, and in particular, horizontal curves on highways have higher accident rates compared to straight roads. Quantitative guidelines for horizontal curve design exist only for flat roads, but not downgrades. This study uses a friction demand versus friction supply approach to check whether the current horizontal curve design policies are acceptable for downgrades. Skid measurements combined with a physics-based tire model are used to obtain the friction supply at various design speeds. This thesis develops analytical as well as low-order simulation-based models for a vehicle traveling on downgrade in order to find the friction demand of the vehicle. Results show that per-axle friction demand can be significantly higher compared to the overall friction demand which is basis of current design guidelines. The margins of safety are shown to significantly decrease with design speed, and in the case of even moderate braking, go to a very low value at high speeds.