Computer simulation was used in this study to examine vehicle stability through lateral acceleration levels. The objective was to compare the minimum flat horizontal curve radius used in traditional geometric design guides with the minimum radius based on vehicle dynamics on three-dimensional (3D) alignments. A vehicle dynamics simulation computer program was used to examine vehicle dynamics and stability on 3D alignments. The program uses a sophisticated two-axle dynamics model that traditionally has only been used by mechanical engineers in experimenting with vehicle characteristics. It was found that vehicle stability is not compromised on 3D alignments compared to 2D alignments for the test cases examined. However, differences in the required minimum horizontal radii were obtained due to the transient effects of a vehicle traveling along a horizontal curve. These transient effects, due to changes in road geometry, include driver steering, vehicle off tracking, and vehicle roll. In order to maintain currently acceptable comfort threshold, increases in the order of 3-16% in the minimum horizontal radii suggested by the current North American geometric design guides are required.

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Conference Canadian Society for Civil Engineering - 30th Annual Conference: 2002 Chellenges Ahead
Furtado, G. (G.), Easa, S.M. (S. M.), & Halim, A.O. (2002). Vehicle stability on combined horizontal and vertical alignments. In Proceedings, Annual Conference - Canadian Society for Civil Engineering (pp. 2503–2512).