Sub-problem 6b: Consideration of a Grade-Separated Flyover

What additional data should be gathered to determine whether grade separation is appropriate? In this limited review of the intersection we have only completed an analyses of questions related to capacity and performance for the peak hour. Justification for a grade-separated flyover must consider the traffic conditions during other hours of the day. Other data such as crash history should be gathered to determine the extent that safety considerations can justify the construction of the facility. Finally, other users such as pedestrians and cyclists should also be considered to determine the extent that a grade-separated flyover effects the connectivity and safety of these modes.

What conflicting movements might benefit from grade separation? There are three crossing conflict points associated with this intersection:

• EB through (2,010 vph) vs. NB left (257 vph)

• EB through (2,010 vph) vs. WB left (120 vph)

• NB left (257 vph) vs. WB left (120 vph)

The most critical conflict clearly involves the eastbound through vs. northbound left-turn movements. A grade-separated flyover for the northbound traffic would eliminate this conflict as well as the conflict between the northbound left-turn and westbound left-turn movements. It would also convert the conflict between the northbound left and westbound through traffic from a crossing conflict to a merging conflict. Recognizing that other grade-separated interchange configurations are possible, we will use the northbound flyover in this sub-problem to illustrate the use of the HCM in assessing the benefits of a proposed grade separation.

[ Back ] [ Continue ] with Sub-Problem 6b