SESSION 8

Shoulder Considerations

Objectives

• Identify shoulder/edge support types

• Describe benefits of each type

• Discuss how edge support conditions are considered in structural design

• Describe benefits provided by shoulder rumble strips

Functions of Shoulder

• Safety zone

• Auxiliary area

• Lateral support to mainline pavement

• Potential traffic lane during rehabilitation

Shoulder / Edge Support Types

• Widened concrete slab

• Tied concrete shoulder

• AC shoulder

Widened Concrete Slabs

• Slab paved 0.3-0.9 m (1-3 ft) wider than usual

• Lane striped at normal 3.6-m (12-ft) width

• Reduces edge and corner loadings

Tied Concrete Shoulder

• Paved concrete slab tied to concrete mainline pavement

• Benefits:

Reduced edge stresses/deflections

Improved lateral support

Reduced moisture infiltration

Design of Tied Concrete Shoulder

• Same thickness as mainline, if paved together

urban: full depth, full lane width

rural: if lesser thickness, granular fill below

• Effective tie system required

minimum No. 5 bar @ 760 mm (30 in)

• Transverse joints match mainline joints

Concrete Shoulder and Slab

Paved Monolithically

D / 3

Sawed Joint

D

D / 2

Deformed tie bar (Minimum No. 5 )

Concrete ShoulderMainline Pavement

Concrete Shoulder and Slab

Paved Separately

D

D / 2

Butt Joint

Concrete ShoulderMainline Pavement

Deformed tie bar (Minimum No. 5 )

Possible Keyway

Improper Tie Bar Installation

Asphalt Shoulder

• AC surface course or surface treatment

• Reduced structural capacity

• No structural support to mainline pavement

• Lane-shoulder joint difficult to seal

• Better visible delineation at night

• Lower initial cost

Consideration of Edge Support in Thickness

Design• 1986/1993 AASHTO Procedure

J factor

Concrete shoulder only

• 1998 AASHTO Supplement

Edge support adjustment factor

Widened slab or concrete shoulder

• PCA

Concrete shoulder reduces edge stress

ShoulderRumble Strips

• Indentations in shoulder

• Create noise and vibration to alert drivers of wayward vehicles

• Effective in reducing vehicle-leaving-the-road crashes

Summary

• Types of shoulders

• Benefits of widened slabs and tied shoulders

• Advantages and disadvantages of asphalt shoulders

• Benefits of shoulder rumble strips