Sub-problem 1b: Maxwell Drive PM Peak Hour - With Conditions

Scenario P-1 is a good place to start our discussion. It represents a legitimate option. The left turns are protected and the lanes are configured in a logical way. (If there are no right- or left-turn lanes, the model assumes the movements are shared with the through movement.) Let's conduct some "what-if" analyses that go beyond the results and data sets presented in the previous Exhibit.

The model estimates a cycle length of 171.4 seconds (for a condition where cycle length is the minimum possible). That’s too long. If the number of northbound and southbound through lanes is increased to 3, as in Scenario P-2, nothing happens. That’s because the through movement is not the critical movement, and so it does not determine the cycle length. If you reconfigure the north and southbound approaches so there are two left-turn lanes and one through-and-right lane, the cycle length drops to 104.5 seconds. This is better, but it assumes it's possible to have simultaneous opposing dual lefts, which isn’t allowed in New York State. If permissive lefts are assumed, the model drops the cycle length to 18.5 seconds. That’s too short for most practical situations. The model is reporting the shortest cycle length that puts the intersection at capacity using the equations used to set the signal timings. A more practical value, like 80 seconds, makes the model show that the intersection is under capacity for that cycle length. At a cycle length of 20 seconds, the model shows the intersection is near capacity and, with cycle lengths of 25 seconds or above, it shows the intersection operating under capacity.

Now we’ll do some sensitivity analyses, mostly to illustrate trends. If we assume dual lefts northbound and southbound, along with exclusive lanes for the throughs and rights, the cycle length drops to 76.5 seconds (from the previous 104.5). If we add dual lefts and three through lanes eastbound and westbound, the cycle length drops to 38.5 seconds. If we take that same lane configuration and consider a more reasonable cycle length, say 45 seconds, the model shows the intersection is near capacity. If we go back to single left-turn lanes northbound and southbound, the model calculates a cycle length of 53.5 seconds.

Discussion:
Notice that we only kept one dataset for all of the planning analysis runs. You can generate the other results very easily. Simply change the lane configuration in the dataset. You might explore other options, too. See if you think the trends in the cycle lengths identified are reasonable given the configuration options you explore.