Towne Pass Curve Correction Project
The California Department of Transportation (Caltrans) proposes to realign approximately 0.6 mile of State Route 190 from post miles 69.2 to 69.8 to the east of the current alignment near Towne Pass in Inyo county, California. The current six curves will be reduced to three. This realignment will cover approximately 6 acres of ground disturbance, improve the horizontal and vertical curves to meet a minimum design speed of 55 miles per hour, increase the stopping sight distance to 600 feet. Paved shoulders will be constructed throughout the project area and side slopes will be flattened or stabilized to create a catchment adjacent to the roadway, thus reducing the potential for rockfall.
The purpose of this project is to improve safety and reduce collisions on State Route 190 in the vicinity of Towne Pass.
The total accident rate in the project area is 4.37 times the statewide average, and the combined Fatal and Injury (Fatal + Injury) accident rate is 7.29 times the statewide average for a similar facility as identified by accident data from 2009 to 2014.
Within the project limits, the current highway alignment consists of six curves, with curve radii of 390 feet, 350 feet, 920 feet, 383 feet, 560 feet, and 2,292 feet, respectively. The standard curve radius for 55 miles per hour is 960 feet. A smaller curve radius indicates a tighter curve, which must typically be negotiated at a slower speed; a maximum comfortable speed for a typical two-lane conventional highway, such as that present in the project area with a curve radius of 400 feet, is 35 miles per hour. Additionally the reversing nature of the curves in the project area create additional challenges and further reduce the comfortable driving speed for the length of the project area.
The stopping sight distance in the project area is as low as 166 feet due to the interaction between crest vertical and horizontal curves. Sight distances associated with this distance would provide for complete stopping only for vehicles moving at about 25 miles per hour. A sight distance of 500 feet provides for complete stopping for vehicles moving at approximately 55 miles per hour.
Paved shoulder widths in the project area range from 0 to 2 feet. Cut slopes are steep, nearly vertical, and are deeply eroded with shallow channels and gullies. Vegetation has not naturally reestablished on cut slopes, and the potential exists for the slopes to shed rocks onto the roadway.