Getting Started

Sequencing, Tools, and Data
Sequencing the analyses is another issue. We’re going to focus on the signalized intersections first, starting at Maxwell Drive (Intersection C), working west to Intersections B and A, then east to Intersections D through G (see Exhibit 2-1). This allows us to study the most affected intersection first, then ones that are less affected because they are further away. We’ll consider the freeway interchange after we’ve finished with the signalized intersections, then we will analyze the arterial segment consisting of intersections A to D.

Choosing the tools to use is another issue. You have to pick ones that strike a balance between the amount of effort they require and the amount of insight they provide. In this case study, we’re going to use three tools. The first is the HCM. We’ll use it for all of the intersection analyses and the location-specific analyses at the freeway interchange. The second is Transyt-7F. We’ll use it to do an arterial analysis of intersections A through D. It will help us ascertain what coordinated signal timings would work best for that set of signals. It should be emphasized that we are using Transyt-7F here to illustrate the use of non-HCM procedures, and other programs could also be used with equal effectiveness.

Since the main purpose of this guidebook is to illustrate how the HCM can be used to study traffic issues, we’ll use this tool wherever possible. We’ll also show where it isn’t applicable, explain why, and illustrate how other non-HCM tools can be used.

In regards to data, we will need three types of inputs: 1) facility-related information (e.g., number of lanes, lane widths, lane configurations, saturation flow rates); 2) traffic-related information (e.g., vehicular and pedestrian volumes for all three conditions); and 3) operational information (e.g., signal timings). We’ll talk about the specific data required for each problem as it is presented. When we reach the system-wide level of analysis, since there are unsignalized intersections on either side of Route 146, we’ll also need behavioral information about the users such as critical gaps and move-up times. We also need to know how NYSDOT designs highway facilities and expectations for operational details (e.g., signal timings). There is some data we won’t need, even though they might be important in other settings. For example, we won’t need any information about on-street parking since none is allowed along any of the streets or highways. We also won’t need information about transit services since no bus routes pass through the study area.

Discussion:
We decided to start the analysis with the most heavily used intersection, and then work first west then east. What would you have done? Is there an advantage to the way we decided to proceed? If you were doing an analysis of the system all at once, might you miss some details if you didn't consider the intersections individually first? What are some of the important consistency issues you have to consider if you look at the intersections separately?

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