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Orientation: Interstate 490 runs left to right, crossing over the Erie Canal at far right. Interstate 390 enters at bottom, ending at I-490. The expressway continues as NY 390. NY 31 (Lyell Avenue) runs left to right at top.
Exit numbers: On I-490, Exit 9A is for I-390 south, while Exit 9B is for NY 390 north. Exit 9B westbound is also signed for NY 31. Similarly, Exits 20A and 20B from I-390 and NY 390 are for I-490 east and west. Exit 21 on NY 390 is for NY 31 (Lyell Avenue).
The interchange: The interchange is a fully directional four-way split, the only example of its kind in New York State. It features left exits and entrances for all left-turn movements, as well as two tri-level crossings. The design presents an appealing symmetry when viewed from above. Notice that the northbound roadway of I-390 and NY 390 passes over I-490, while the southbound roadway passes beneath. The east-to-north ramp from I-490 forms the top layer of its tri-level crossing, while the west-to-south ramp forms the bottom layer.
Those ramps connecting points east and north provide two full lanes, to accommodate heavy commuter traffic between Rochester and its northwestern suburb of Greece. The westbound-to-southbound ramp provides two lanes as well, to serve traffic bound for the airport just off Interstate 390. All other ramps consist of a single lane.
In close proximity to the main interchange, NY 390 has a six-ramp, partial cloverleaf interchange with NY 31. The two-lane ramp (Exit 9B) from I-490 west to NY 390 north feeds directly into the two-lane exit ramp to NY 31. Traffic bound for NY 390 must change lanes quickly at the merge point, while NY 390 traffic exiting at NY 31 must cross over equally quickly. To alleviate this problem, signage for the right lanes at Exit 9B indicates an exit-only lane for NY 31, while the left-lane is signed as Exit Only for NY 390, despite the fact that a lane change is still required. (This is a slightly different configuration from that shown in the photo above, being a fairly recent modification.) The eastbound Exit 9B ramp provides no access at all for NY 31. It joins the single through lane of NY 390 after the Exit 21 ramp diverges.
This interchange complex is being studied for possible
improvements, mainly to eliminate weaving motions inherent in the