Morrisville Engineering, Design, and Construction Manual - July 2016

Section 4: Access and Circulation 4.2 Streets and Alleys 4.2.9 Roadway Horizontal and Vertical Alignment Standards

Table 4.2.9.D: Horizontal and Vertical Curve Controls

Horizontal Curve Controls

Vertical Curve Controls

Minimum Rate of Vertical Curvature

Design Speed (mph)

Minimum Design Vehicle [3]

Curb Return Radius (ft) [1]

Street Classification

Centerline Radius (ft)

Minimum Length (ft) [2]

Maximum Supereleva tion (ft/ft)

Use

Maximum Grade

Crest Sag

Residential [4] Nonresidential, Multifamily, & Mixed-Use

<20

0.02

20-40

5

10%

10

17

N/A

SU

Driveways

Garbage Truck

<20

0.02

50-100

30

10%

10

17

N/A

0.02 reverse crown 0.02 reverse crown normal crown reverse crown Normal crown

Garbage Truck

Residential [4]

5-10

50

30

10%

10

17

50

Alleys

Nonresidential, Multifamily, & Mixed-Use

Garbage Truck

5-10

50

30

10%

10

17

50

Minor

All

25-30

90-230

30

10%

18

18

100

Local Streets

Major

All

25-35

140-375

30

10%

20

28

120

Main Street

All

25-35

140-375

30

5%

20

28

120

Town of Morrisville Fire Truck

Residential [4] Nonresidential, Multifamily & Mixed-Use

35-45

0.04

225-665

30

10%

28

35

150

Collector Street

40-50

0.04

490-930

40

10%

55

55

150

Minor Thoroughfare Major Thoroughfare

All

Defer to NCDOT Standards

All

Defer to NCDOT Standards

Notes: mph = miles per hour; ft = feet [1] Measured from the back of curb. [2] L = KA, where L = Length of vertical curve in feet; K = Rate of vertical curvature in feet per percent of A; and A = Algebraic difference in grades in percent. [3] See the UDO for additional requirements for streets with medians. [4] Residential uses include single-family attached, single-family detached, duplex, and manufacture home dwellings. All other residential uses are classified as nonresidential, multifamily, and mixed-use for the purpose of determining horizontal and vertical curve controls. General Vertical curves affect the gradual change between grades of a vertical alignment. The curves should produce a design which provides adequate sight distance, for stormwater runoff drainage, and rider comfort. To meet these criteria, the vertical curves are designed to curve at rates specified in Table 4.2.9.D, Horizontal and Vertical Curve Controls. The product of the curvature rates and the algebraic difference in adjoining grades is the basis for the minimum length of curves, but should never be less than the minimum lengths provided in Table 4.2.9.D, Horizontal and Vertical Curve Controls. 2. Crest Vertical Curves Vertical Curves 1.

The design of crest vertical curves shall provide sufficient sight distance.

3.

Sag Vertical Curves

a. The rate of vertical curvature should provide a minimum grade of 0.003:1 (vertical: horizontal) within a 50-foot distance from the level point.

b. Sag vertical curves in cut situations should be avoided to prevent ponding of water.

January 2016

Morrisville, NC

Page 20

Engineering, Design, and Construction Manual