Interchange Index
I-88, I-355, and US 34
Downers Grove, IL
Overhead Picture from terraserver-usa.com
Overview: The junction of I-88 (also known as the East-West Tollway) and I-355 (creatively enough, the North-South Tollway) is a rather large junction. I-355 and I-88 run parallel to each other for almost 3 miles, while skirting around the southeast corner of the Morton Arboretum. The ramps in the interchange are split into two main clusters, one at each point where I-88 and I-355 split apart to go on their merry ways. The picture above shows a zoomed-out view of the interchange as a whole; each of the two clusters is shown below in greater detail. (I could have gone for one picture, but it was pushing 2000x2000 pixels and would have been nearly impossible to view on a dialup connection.)
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The Northern Half: In this photo, I-355 enters from the north and leaves to the south as the highway in the middle. I-88 enters from the south on the right, and leaves to the northeast. The local road running to the west of I-355, and then crossing under it, is Finley Road; this road plays no direct role in the interchange. Five of the eight connections are included in this half of the interchange. The northernmost is a ramp from I-88 WB to I-355 NB; it crosses over Finley Road, and then has an at-grade connection with an entrance to some sort of tollway maintenance area. (This facility is partly located under a flyover ramp, and also has connections to I-355 NB and Finley Road.) Both ramps from I-355 SB branch off at the same point, and then split just before crossing I-355. At the same time, the second exit from I-88 WB splits off, and runs parallel to Finley Road as it crosses under I-355 to join the SB lanes. The last ramp in this half is a flyover from I-88 EB to I-355 NB, located at the southern end of the aerial photo. |
| The Southern Half: The southern half of the interchange includes the remaining three connections between I-355 and I-88, as well as full connections to and from US 34. Traveling northbound on I-355, a ramp splits off a considerable distance south of the interchange for I-88. This ramp crosses US 34 on an overpass, and then splits between I-88 WB and EB. The interchange between I-355 and US 34 is a fairly straightforward diamond interchange, with some extra ramps added to serve traffic to and from the west. The onramp to I-355 north splits to give access to the I-88 WB onramp, and the ramp from I-88 EB to I-355 SB has an exit for US 34 before it crosses over the offramp from I-355. Notice that the two ramps between US 34 and I-88 to the west have toll booths; this is done so that traffic can't exit at the next exit to the west, at IL 53, without paying a toll. Two interesting points on bridges: (1) check out the three-level crossover where I-355, the 355 NB->88 WB ramp, and Warrenville Road (parallel to and north of US 34) meet; and (2) notice that all of the bridges under I-88 are actually tunnels, which traffic enters a little bit before actually crossing under I-88. I'm not sure why this was done.... maybe for easier snow plowing on I-88 without dumping it across 355? It's really noticeable on I-355 on the north end of its underpass. |
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Comments: This is really a good connection between two highways, both of which are quite important in the Chicago transportation system. I-88 is a major highway for commuter traffic between downtown and the western suburbs; I-355, along with I-290 and IL 53, is currently a partial western bypass, and it could eventually become a full quarter-circle from I-94 down to I-80 (or even I-57...?) That said, Illinois did what they had to to make the interchange effective; for starters, traffic can move between the major arterials almost completely without slowing down. The curves on many of the ramps are wide enough for 40-50 mph traffic. However, it's not terribly space-intensive either; a major 4-way interchange with no loop ramps usually becoms some sort of sprawling behomoth that's only possible to build in a reasonably rural area or by buying up a ton of property. Here, however, the designers did a nice job of curving the interchange around the end of the Morton Arboretum, and clustering the ramps where the highways split on either end. A classic cheap-out in a situation where two highways run adjacent to each other is to merge all of the traffic together, and then split it apart a mile later. This generally results in a long stretch where traffic is weaving all over the place, causing many accidents; the designers chose wisely in avoiding that plight. They even used space inside the interchange efficiently in the northern half, with some sort of a maintenance facility wedged between a tollway, a ramp, and a local road and under a flyover ramp. All said, this one's pretty nice.
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Corrections? Suggestions? More information is always welcome.
Suggestions for more interchanges to cover on this site are great too.
Contact the author, Dan (known as DanTheMan on misc.transport.road):
twowheel@email.com
