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Street Infrastructure
In this third subset of the Corridor typology, we
considered all types of streets and roads, from free-
ways to local neighborhood streets. This hierarchy is
shown in red in Plate 16. 
We recommended four actions:
1.
Eliminate a portion of planned freeway that
dumped traffic into the center of Morrisville for no
apparent reason.
2.
Improve east-west connections by extending three
local main roads to form a more coherent network
for the study area.
3.
Create greater connectivity of neighborhood streets.
4.
Establish design criteria for streets that include
pedestrian and bicycle facilities.
Of most interest to the reader will be the connec-
tivity index and the street designs. One of the funda-
mental principles of New Urbanist design is that all
neighborhood streets be multifunctional, that is, safe
and attractive for pedestrians and cyclists as well as
for cars, and that they connect to form a network
with multiple choices of routes. This connectivity
spreads out traffic more evenly and reduces conges-
tion, but this pattern contrasts markedly with most
new development in the CORE area, which has been
designed with few points of access, often with only
one way in or out. This is true of office and industrial
parks as well as residential neighborhoods.
It’s hard to overstate the importance of connecting
streets into a network. Mobility for vehicles, bicyclists,
and pedestrians increases and costs of civic services
(public transit, school buses, police, fire and ambu-
lance services) are decreased by having more conve-
nient choices of routes around any neighborhood or
district. This same flexibility increases the efficiency of
these emergency services as they’re able to respond
faster to emergencies. Street connectivity can even
lead to improved water pressure and easier mainte-
nance of the underground pipes by looping lines
through a development rather than creating dead ends
in cul-de-sacs.
In projects covering a smaller area, we normally
plan out the entire street network, but here we
amended the larger regional framework of arterials,
established guidelines for the street pattern in the
multiuse centers, and set our performance standards
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for all future neighborhood street connectivity. In
this way a connected network of streets will grow in
step with new development.
We based our connectivity index on one already
implemented in the study area by the town of Cary.
This index measures the number of ‘links’ (defined as
street intersections and cul-de-sac dead ends) and the
number of ‘nodes’ (segments of streets between links,
and street stubs that end at property lines for future
connections) (see Figure 7.2). In this figure, links
are represented by black circles and nodes by stars. In
the diagram there are 11 links and 9 nodes. Dividing
the number of links by the number of nodes results
in a connectivity index of 1.22.
A perfect grid has a connectivity index of 2.5.
Most conventional cul-de-sac subdivisions yield an
average connectivity index of only 1.0. We recom-
mended a connectivity index of at least 1.4–1.5,
though variations could be granted in a few cases
where severe topographic conditions make connec-
tions very difficult and expensive. In these situations,
cul-de-sacs may be used, but these dead-end streets
must be strictly limited to preserve the integrity and
performance of the connected street system.
The connectivity of streets is not the only impor-
tant issue in their design. The correct design details
to accommodate pedestrians and cyclists are also very
necessary for the network to be attractive and
function well. Though the RTP and several of the
municipalities in the area have installed sidewalks
and bicycle paths, or have recently begun requiring
them, such facilities are noticeably absent on many of
the area’s local streets and thoroughfares. This omis-
sion is compounded by the fact that even where
sidewalks and bicycle facilities exist, there are often
gaps between segments, significant barriers to their
use (such as major thoroughfares, or wide intersec-
tions on roads without islands for pedestrian refuge)
or pedestrian-unfriendly developments that discour-
age walking and cycling.
To help remedy these deficiencies, we recom-
mended that new streets and improvements to exist-
ing streets should, at a minimum, have five-foot wide
sidewalks on both sides to permit two adults to walk
comfortably next to one another. Collector streets
and thoroughfares should also be retrofitted with
wide outside lanes for cyclists. Alternatively, multiuse
paths at least 10-feet wide that can be safely used by
both pedestrians and bicyclists should be constructed
alongside roadways. Figure 7.3 illustrates an appro-
priate design for a multiuse path in cross section. In
addition to pedestrian and bicycle facilities along