Interchange of the Week
Monday, 3 November 2003

I-86 & I-390, Avoca

NY 15 & NY 17

Orientation: Interstate 86, overlapped by NY 17, runs from left to bottom right. Interstate 390 branches toward the upper left. NY 15 overlaps I-390 and I-86 from top left to bottom right. NY 415 cuts across the lower left.

Exit numbers: From I-86/NY 17, Exit 36 is for I-390. This interchange is not numbered from I-390, as it is the route's southern terminus. (The northern terminus is shown at Week 33.)

The interchange: Often, when one freeway ends at another, the interchange used is T-shaped and seems to favor all traffic movements equally, as in Week 21, Exit 8. In many other instances, such as this one, it is not clear which freeway is ending and which is the through route. In this example, from I-390 to I-86 east, or from I-86 west to I-390, is really the straight-through movement, with I-86 west branching off.

Furthermore, many such interchanges have a configuration more Y-shaped than T-shaped. Here, movements between points west and north are not as favored as those to and from the southeast. The ramp from I-390 to I-86 west is tightly curved, making almost a full U-turn, and is only one lane wide. The ramp from I-86 east to I-390, also one lane wide, actually turns through more than 180 degrees, as it swings around the outside of the roadways it connects. For other movements (to and from the southeast), two lanes are provided. It is geography which accounts for this one-sidedness: to the west of this point is a range of hills preventing more direct access in that direction. Most traffic travelling between points north and west use local highways like NY 36, some twenty miles to the west.

This interchange might be termed a semi-directional Y with U-turns. A directional-Y (with semi-directional U-turns) would look like Week 57, Exit 24.

At the corners of the photo, dead end roads can be seen parallel to the freeway, on either side. These are part of an old back road, itself following and old railroad grade, between Avoca to the northwest and Kanona to the southeast. The northwestern stub is Kanona Road and the southeastern is North Main Street.