Civil Engineering Reference
In-Depth Information
17.2.4.1 Applications
Since the 1970s the pace of new general purpose roadway construction has slowed
down. Some freeway reconstruction and expansion are still needed to reduce
recurring congestion, to improve safety through the removal of design de
ciencies
on existing facilities, and to better integrate major roadway with their surrounding
neighborhoods.
General-purpose roadway construction and widening is most frequently imple-
mented in areas experiencing rapid population growth. It usually consists of
building new freeways and arterials or adding lanes or shoulders to existing
facilities. This strategy is often implemented in the fast growing areas in the south
and west of the US (e.g., Dallas, Houston, Phoenix, Atlanta) where land for
highway construction is more available. However, in the built up metropolitan areas
of the northeast (e.g., New York, Boston, Philadelphia) physical and environmental
constraints on highway expansion usually limit the opportunities for major new
road construction.
There are several notable examples of new road construction that address
both
congestion and quality of life concerns. These include Boston
'
s Central Artery
“
”
Tunnel (the
Big Dig
) and a new cable stay bridge across the Charles River that have
signi
cantly reduced congestion and created a linear park over the tunnel; Seattle is
fitting its long standing Alaskan Way Viaduct with a new tunnel that will result in
faster traf
c movement and improves access between the city and Elliot Bay.
Most freeway construction, however, is now in the form of tolled facilities
—
both
as a
financing mechanism and to control demand through pricing. Compared to un-
tolled new roads, tolled facilities have the potential of maintaining desirable operating
speeds in the long term if tolls can be increased in response to increased demand.
17.2.4.2 Guidelines
New freeway and arterial roadway designs should re
fl
ect the design standards and
guidelines set forth in the AASHTO
“
Green Book
”
[
15
].
c guidelines from a planning, design, and mobility perspectives
include the following:
Some speci
Complement rather than compete with rapid transit lines
For right hand driving, locate all entrances and exits to the right of the main
travel lanes
Limit
freeway interchanges to four
legs
—
especially where two freeways
intersect
Avoid short or complex weaving sections
“
”
Maintain
to avoid bottlenecks (when 2 lanes merge with 3 lanes,
5 lanes should be provided past the merge point)
lane balance
Do not converge freeways in areas of high trip density
Connect
—
not split
—
areas or neighborhoods.
