Chapter 13 - Traffic Forecasting and Analysis Concepts

13.3. Arterial Traffic Analysis and Design

13.3.3. Intersection Traffic Control Design

After the typical section is determined and the location of median breaks are determined (if the facility is divided), the traffic analysis should then focus on the intersections. It will be necessary to determine the type of traffic or right of way control and the need for turning lanes. Since the type of traffic control affects the intersection design, it is first necessary to determine if traffic signal control will be needed. An example of this influence on intersection design is that designers will typically limit the number of lanes on stop controlled approaches to avoid vehicles stopping abreast of each other and blocking sight distance from the other vehicle. When multiple lanes are needed on stop controlled approaches, the design will include islands and/or increased turning radii to separate through and turning vehicles.

The need for traffic signal control is obvious at many intersections that are currently signalized. However, at other intersections traffic signal warrant analysis may be needed to establish the need for traffic signal control. At some intersections, where traffic signals are not currently needed, future traffic increases may warrant signal control. For such intersections, a warrant analysis should be conducted for both the construction year volumes as well as for the design year volumes. Warrant analyses should be conducted using the guidelines of the most current edition of the Manual on Uniform Traffic Control Devices (MUTCD).

Signal warrants are typically conducted using hourly volumes throughout the normal day (not just peak hour volumes). Since the design volumes are limited to peak hour and daily volumes, it will be necessary to derive estimates of the volumes that occur during the remaining hours of the day.

An important signal warrant is Warrant 1, Eight-Hour Vehicular Volume. Therefore, the traffic analysis should estimate the eighth-highest volume of the day. The eighth-highest volume can be compared to the requirement of Warrant 1 to estimate if this important warrant will be satisfied with the projected volumes.

 

The eighth-highest volume can be estimated as representing 6.25 % of the daily volume. If the eighth-highest volume exceeds the minimum volumes for Warrant 1 using the construction year volumes, then signal control should be considered for installation during the construction project.

If Warrant 1 is only met using the design year conditions, then signalization may not be included with construction, but the design may reflect the need for future signal control. For example, turn lanes may be constructed and striped out until signals are installed.

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