Introduction - Page 2 of 3
The overall subarea network that is
the focus of this case study is shown in Exhibit 4-3. Alternate Route 7 is in the middle
of the figure. I-87 is on the left and I-787 is on the right. The drawing is
not to scale and the Alternate Route 7 segment in the middle has been
While congestion in
the Alternate Route 7 subarea network is not bad overall, there are two
places where significant queuing takes place: the I-787 interchange (viz.,
right-hand ramp leading from NY-7 East to I-787 South); and the I-87
interchange (viz., the right-hand ramp leading from NY-7 west to I-87 north). In
both cases, the queues can be more than a mile long when traffic is heavy.
For example, some mornings the line for the right hand ramp at the I-787
interchange extends halfway back to I-87. Similarly, on Fridays, especially
in the summer, and on many weekday afternoons, the queue for the right-hand
ramp from NY-7 and I-87 extends halfway back to I-787.
Alternate Route 7ís
basic freeway section is about four miles long, with two lanes eastbound and
three lanes westbound. The third lane westbound is used by trucks that are
climbing the grade that starts at the Hudson River and ends near Miller
Road. From there to I-87, the third lane becomes an extension of the
right-hand ramp leading to I-87 north.
The interchanges at
either end of Alternate Route 7 are good facilities to study. The I-787
interchange has short weaving sections, complicated merging geometries with
tight geometry, and an auxiliary lane eastbound that separates the ramps
from the main traffic lanes. The I-87 interchange has similar problems with
short weaving sections and complicated merges and diverges.
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