Subproblem 2d: How
Can We Improve the Level of Service at the Ramp Junction at the Northbound OnRamp to
I87?
Step 1. Setup
The merge point that we considered in subproblem 2c was
over capacity during the PM peak hour. Queues extended over much of
the length of the ramp. The demand exceeded capacity and the HCM
methodology couldn't be used for this analysis under conditions
present during the PM peak hour. But while the HCM methodology
couldn't forecast the performance, we do know that the facility will
fail since the demand was found to exceed capacity.
Consider how we could mitigate this problem. What possible
changes in the design of the ramp merge area should be considered? To
provide insight into possible geometric mitigations, we can look more
closely at the forecast models. There are five variables of prime
importance:

Free flow speed on the ramp.

Free flow speed on the mainline.

Number of lanes on the ramp.

Number of lanes on the mainline.

Length of the acceleration lane in the merge area.
Many factors determine whether or not changing any
of these variables is feasible. But we can use the HCM procedure
to determine how much change we can expect in the operational
performance if one or more of these variables is modified.
Discussion:
What possible design changes would you suggest to mitigate
this problem? When you are ready, continue to the next page.