Overview: This interchange is one of many in the Detroit area which garner a little interest. I-96, coming from Lansing and Brighton, enters from the northwest and leaves in a southerly direction. To the south, it is also multiplexed with I-275; this was the result of a former proposal to extend I-275 northward to rejoin I-75 and form a complete western bypass of Detroit. Going directly east fron this point is I-696, which travels across the northern side of the Detroit area and ends at I-94 some 27 miles later. Michigan State Route 5 also travels through here; it truns from near downtown Detroit northwest to Farmington, and then runs on a freeway alignment around the south side of that town. The highway to the north is also part of M-5, although it is only a freeway for one more interchange before becoming an expressway with at-grade intersections. I believe a northward extension is planned for this highway in the near future.
Interchange Description: Five-way interchanges are always fun, and this is no exception. I think the easiest way to look at this one is to simply look at the choices a driver is faced with as he enters on each of the five roadways.
From I-96 EB: Entering the interchange from the west, the first split is pretty major. Here, traffic going to I-696 and M-5 eastbound exits left, while through traffic on I-96 and traffic for the M-5 connector keeps right. Shortly afterwards, a loop ramp for the M-5 connector leaves the far right side. The left branch of the original split is later divided between I-696 (to the left) and M-5 (on the right) in a basic directional Y-interchange.
From I-96 WB/I-275 NB: Notice that I-275 and I-96 enter the interchange as a pair of parallel carriageways, and not as a simgle roadway. The split between these two occurs quite a good distance to the south. The left side is the I-96 mainline, which curves through the entire interchange without any exits or entrances until it meets I-696. The right side is a ramp which has exits for M-5 east and I-696 east before an entrance from I-696. If/when I-275 is extended to the north, to rejoin I-75 in Clarkston, this right half of the carriageway will become the I-275 mainline; however, at the moment, I-275 NB ends just south of this interchange. The next exit is for the partial cloverleaf at 12 Mile Road to the north; more on this later.
From M-5 WB: Again, there is a major split before entering the interchange. This time, the right fork splits between I-696 EB and I-275/M-5 connector NB, and the left fork leads to I-96 WB and a cloverleaf loop to access I-96 EB/I-275 SB.
From I-696 WB: At the najor fork in the westbound lanes of I-696, the only traffic that exits left is that bound for I-96 WB. This probably constitutes the majority of traffic traveling west on I-696. The remainder of the traffic exits right, and then has the choice of exiting first for the M-5 connector north, second on a loop ramp for M-5 east, or continuing straight ahead to join the eastbound lanes of I-96 and the southbound lanes of I-275.
From the M-5 connector SB: First, notice the collector-distributor road for the 12 Mile Road interchange; traffic can exit onto this road from a point just north of the satellite photo's coverage. The first ramp, a right exit to I-96 west, leaves from this C/D road before it rejoins the M-5 mainline. The mainline then splits, with the right half of the traffic going to I-275/I-96 south/east and the remainder going to M-5 east. Traffic bound for I-696 east can take the ramp to M-5 east, and then use a loop ramp to exit to I-696.
The 12 Mile Road interchange: The interchange at the intersection of the M-5 connnector and 12 Mile Road, just north of the bulk of the junction, is, at first glance, a fairly straightforward 6-ramp partial cloverleaf. However, there are a couple of items that warrant particular notice. First, there are collector-distributor roads on the M-5 connector; these are rare in a 6-ramp interchange, because there is no weaving on the mainline; all of the entrances occur after all of the exits. These C/D lanes are really present more to help traffic from the I-96/I-696 junction get through the interchange without great amounts of weaving on the mainline of the M-5 connector. Second, take a look at the small ponds in the NE and SW quadrants of the interchange, and then look right around the edges of them. With a little imagination, I can discern the former route of the 'missing' cloverleaf ramps around these ponds. I don't know if this was once a full cloverleaf, or my imagination is just running wild, but it's worth noticing.
History: This interchange was built in a number of stages; below is a map of the interchange from terraserver-usa.com to illustrate. This was taken right from a USGS quadrangle. At the time the map was first published, there was simply a fully directional split between I-96/I-696 and M-5. (Interestingly enough, M-5 is shown as State Route 102; that must have been changed somewhere along the line.) This is shown in red. Later, the connections to I-96 south and I-275 were added; these are in purple. hhe M-5 connector was added last; this isn't shown on the map, as it occured fairly recently.
Comments: It's a complete 5-way interchange, with no connections missing. That in itself is remarkable and pretty rare. All of the ramps for major connections (I-96 <-> I-275, I-96 <-> M-5, I-96 <-> I-696, I-696 <-> I-275, I-275 <-> M-5 connector, and M-5 connector <-> M-5 mainline) are well-built, with no loop ramps and wide radii of curvature. There's a little weaving, but that's virtually unavoidable. All things considered, I'd say that this interchange is very well-designed for the situation.