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Sub-problem 3b - Page 7 of 10 |
ID# C403B07 |
Sub-problem 3b: Ramps
Locations I and J
Our merging analyses focus on locations I and J. Location I involves a
single lane on-ramp and a 2-lane freeway. This is a typical situation. The
acceleration lane is about a tenth of a mile long and the ramp has a free
flow speed of 25 mph.
Location J is about
3-tenths of a mile further downstream. The free flow speed on the ramp is 35
mph. It has a single lane, right-hand on-ramp and a 2-lane freeway, but the
on-ramp never ends, making it different from a typical merge location. The
on-ramp continues on as a third lane. To study it as a merge, we will do a
parametric analysis and vary the length of the effective on-ramp to see what
LOS we might expect. The HCM also suggests that we do an analysis of the
approach leg and departing freeway capacities. These analyses can be done
using the HCM suggested capacities provided in Exhibits 24-3 and 24-7.
We know from capacity
analyses in the previous section that the v/c ratio is 0.98 for the I-787
NB/Route 7 WB ramp (Location I) and 0.15 for the I-787 SB/Route 7 WB ramp
(Location J) in the PM peak hour. So we may find that the merge at Location
I is problematic, while the one at J is not.
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Exhibit 4-59.
PM peak hour analysis results at Locations I and J |
|
Location |
Density
pcpmpl |
LOS |
|
I |
216 |
C |
| |
|
Location J |
v/c |
|
On-ramp |
0.34 |
|
Arriving Freeway |
0.54 |
|
Departing Freeway |
0.46 |
The analysis results,
for the merges at Locations I & J, during the PM peak hour are shown in
Exhibit 4-59. What we see is that
the merge at Location I is operating at a LOS C. This suggests that although
the performance of the ramp itself may be poor (v/c=0.98), the merge is able
to accommodate the traffic. At Location J the capacity analysis indicates
the merge is well under capacity.
