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Design Guidance
6.4 Intersection Design Guidance
Basic costs for intersection treatments are indicated in Figure 6.12 (C). The actual
cost will vary somewhat depending on the size (number and width of lanes) as
well as the traffic control devices already in place. Crossing width is used to de-
termine whether to use a mast arm rather than a strand wire signal. Up to 70 feet
is a reasonable length for a mast arm; longer crossings are permissible, up to 84
feet, but the width of the base, foundation and other materials increase. Three
to four feet at the tip of the mast arm is reserved for a sign, and about 16 feet at
the pole end is needed to clear the sidewalk and buffer. This translates into a
functional crossing width of about 48 feet, or four lanes of traffic.
Because intersections are such highly visible locations, they get noticed much
more than other parts of the street. Therefore, textured / colored pavement
treatments, wayfinding signage, and quality amenities like furniture and pedes-
trian-scale lighting features tend to have superior cost-benefit characteristics.
The design criteria in Figure 6.12 (D), adapted from the NCDOT Traditional Neigh-
borhood Design Manual, may be adjusted according to NCDOT standard poli-
cies on state-maintained streets inside of Morrisville. These criteria fit pedestrian-
oriented areas; higher design values may be required on higher-speed streets
with little pedestrian and bicycle activity.
Figure 6.12 (B) illustrates some common design considerations.
A. Ensure that all intersections have ADA curb ramps designed to
NCDOT and national specifications, and that other features like
light poles (shown here with a required pedestrian countdown
signal head) allow for easy movement of wheelchair users.
B. Wayfinding signage should be consistent, and consistently
located to ensure high visibility. Again, allowing for at least
40” of clear space around the sign is desirable, as are viewing
characteristics that support ADA populations.
C. Similarly, water fountains like the one shown here should allow
maneuverability without sacrificing accessibility.
D. Waste receptacles should be conveniently-placed, highly visible,
and emptied frequently.
E. The curb extension shown here is desirable in downtown locations
to help reduce pedestrian crossing distances, provide a more
secure parking area behind the extension, and slow traffic
turning speeds.
Intersection Treatments and Amenities
Typical
Cost
Cost Unit
Basic Infrastructure
Sidewalks
$53 linear foot
Curbing
$27 linear foot
Signal Mast Arm with Signal*
$150,000
each
Signal Mast Arm (Double) with 2 Signals* $175,000
each
Strand (Wire) Signal Pole with Signal*
$80,000
each
Pedestrian Signal
$1,900
each
Sign and Post
$250
each
Wayfinding Sign
$500 -
$1,000
each
ADA Ramp
$1,200
each
Amenities
Bike Racks (Inverted 'U', 2 bicycles)
$700
each
Crosswalk (Tape, Transverse Lines)
$100
each
Crosswalk (Tape, Ladder)
$300
each
Crosswalk (Textured Concrete)
$20,000
each
Refuge Island
$10,000-
$40,000
each
Curb Extension
$10,000
each
corner
Raised Crosswalk (Speed Table)
$2,500
each
Speed Hump
$2,000
each
*Note: Does not include site-specific cost of installation, e.g.,
electrical and wiring, foundations.
Street Intersection
Land Use
Posted Speed Curb Radius Planting Strip Sidewalks
Bike Treatment
Alley
Commercial
<20mph
15'
0' - 3'
None
None
Local - Residential
Low-Density Residential
25mph
15'
3'
5' one side Wide Outside Lane
Local - Activity Center Mixed Residential-Commercial
15-25mph
15'-20'
6' or greater 8' two sides Wide Outside Lane or Sharrows
Collector
Mixed Residential-Commercial
25-35mph
20'-25'
5' Min.
5' two sides Wide Outside Lane or Sharrows
Minor Arterial
Medium Density Res.-Commercial 35-45mph
25'
8' Min.
5' two sides 4' - 6' Bicycle Lane
Major Arterial
Commercial
35-55mph
25' +
8' Min.
5' two sides 6' Bicycle Lane
Intersections at roadways deserve special treatment and consideration
in the planning and design processes for several reasons:
•
Intersections are where the majority of conflicts between cars,
pedestrians, and cyclists occur;
•
Intersections mark transition zones between one type of road-
way and another, often with each road having different capac-
ity and speed characteristics; and
•
Intersections are the places where the highest land values and
most space are typically provided, often generating higher in-
tensity developments than typically occur mid-block.
Streets and intersections can be broken down into five categories, as
shown in Figure 6.12 (A). The street zone is everything between the curb
lines; but what happens in the other four zones leading into the built up
area is equally as important to ensure compatibility between street and
development design. The width of each area depends on the intensity
of the land use and the amount of available right-of-way and setbacks
from buildings. Narrower setbacks may be desirable in lower speed ar-
eas to help create the feeling of an enclosed space to slow traffic and
create a more walkable community. In such cases, the Streetscape and Amenity Zones
are often one and the same, and the door zone becomes narrow with special attention
paid to entranceways and window-driven retail opportunities.
Figure 6.12 (A)
Figure 6.12 (B)
Figure 6.12 (C)
Figure 6.12 (D)