01514489

Component

AASHTO guideline for geometric design of highways requires that insides of horizontal curves be cleared of obstructions to provide at least stopping sight distance. The guideline has a method for determining the extent of horizontal clearance or offsets. For vertical clearance, the guideline suggests use of 2.75 ft as maximum height above driver path for objects located on the far edge of the clear area. However, the horizontal offsets and the 2.75 ft are suitable for middle sections of long horizontal curves with constant grade. Applying the horizontal and vertical offsets to sites with overlapping horizontal and vertical crest curves may result in deficiency in required sight distance. This study developed an analytical model for determining roadside vertical clearance offsets where horizontal and crest curves overlap. The model includes such factors as grades, driver location, driver eye height, object height, sight distance, length of vertical curve, length of horizontal curve, and superelevation. Using the model, 3D clearance design charts were developed. These charts will be useful to practitioners in designing vegetation clearance, side slopes, as well as dimensioning roadside barriers and retaining walls.

This paper was sponsored by TRB committee AFB10 Geometric Design. Alternate title: Maximum Height of Roadside Objects on Inside of Horizontal Curves.

01503729

14-0782

English

20p

2014

Transportation Research Board 93rd Annual Meeting

Digital/other

Figures; References

Design charts; Height; Highway curves; Mathematical models; Roadside structures; Sight distance; Vegetation

Crest vertical curves; Obstructions (Sight distance)

Design; Highways; I20: Design and Planning of Transport Infrastructure

Transportation Research Board Annual Meeting 2014 Paper #14-0782

TRIS, TRB, ATRI

Jan 27 2014 2:20PM