Sunday, August 12th, 2007
On the heels of the very successful I-465 northwest fast track project that upgraded a short segment of that highway from 71st St. to 86th St., INDOT is kicking off a six year project to redesign, reconstruct, and widen 11 miles of I-465 on the west side. INDOT has a project web site for this, but it appears rather stagnant.
Now that work is officially underway on this project at 38th St., it is worth taking a look at what INDOT has done on this project. On the whole, I think it is shaping up to be another excellent project, with one interchange I find particularly successful. This comment applies to about 80% of the project. There is, alas, another 20% that is seriously deficient. This post will focus on the good stuff, and I’ll post a subsequent post on the bad.
I-465 on the west side was one of the earliest segments of the highway to be built. I believe it was originally actually built as four lanes, but was shortly widened to six. Like many INDOT suburban expressway, this one was built with minimal ROW, substantially complicating an upgrade. Don’t get me wrong, I don’t think gigantic ROW’s through an urban area are necessarily a good idea, but they definitely come with their downsides. The good news is that INDOT has a number of closely spaced interchanges to provide real local access to the west side. This isn’t a highway like I-70 on the east side, with widely spaced interchanges that simply is a huge great wall through neighborhoods that it harms and does not serve. This section of I-465 is not like that. But that comes with a downside of weaving traffic and less operational efficiency. What’s more, INDOT used a lot of full cloverleaf interchanges, which are less widely used today because of the weaving traffic they generate. Finally, enormous growth on the west side, especially in Hendricks County, has been pumping large amounts of traffic into I-465. If transportation officials are able to secure the funding to upgrade routes like 10th St. and Rockville Rd., the traffic levels hitting I-465 will expand proportionally.
To to summarize, pavement age, lack of capacity for the future, and inefficient interchange designs, along with some design standards issues, have led INDOT to completely redesign the roadway to improve things. The total project cost is around $400 million.
The first point to consider is the average cross-section of I-465. Today it is a six lane roadway. There were two basic designs considered by INDOT: an 8+2 cross section with four mainline lanes in each direction plus an auxiliary lane between interchanges, or a 10 lane cross section with five mainline lanes in each direction and no auxiliary lanes. A study of a 10+2, possibly the “ideal” cross-section, was not undertaken as near as I can tell.
Let’s be blunt here. INDOT is spending $400 million to add only one lane in each direction. This is the minimum possible widening. I’ve been highly critical of this in the past, and especially critical of how INDOT mis-represents this to the public by counting auxiliary lanes as mainline lanes when they manfestly are not. However, in this case, I do feel INDOT has made a reasonable tradeoff. With the number of homes and other buildings close to the freeway and the narrow ROW available, expansion beyond eight lanes would have been very costly and very damaging to the neighborhoods. This project is already causing a significant number of residential relocations. Clearly, minimizing this is a good goal. So if 10+2 if not realistic, 8+2 is probably a better choice than 10+0, because of the closely spaced interchanges and weaving traffic that results. So while this minimalist approach has been something I’ve not been happy with in the past, particularly on the northeast side, I think all things considered it was probably the right approach here. I’ll assign a Capacity grade of B.
Moving on to the interchanges, it appears to me that with most of them INDOT has gone with the same approach that it took at 71st St. and 86th St. Namely, these are going to be very high capacity, and represent a major, major improvement. What’s more, it appears that a lot of work went into the aesthetics and pedestrian/bicycle access. Unfortunately, the details available on the web here are extremely sketchy and I haven’t had the leisure to track this down with INDOT, but it sounds like they really did a lot of excellent work in terms of working with the neighborhoods and putting in great design elements. For example, most of the bridges are supposed to include “pedestrian promenades” to safely carry pedestrians and bicyclists across the freeway. Even if the project only lives up to the northwest fast track standards, it will be great. And I’ve got an inkling from what I’ve read that it might be even better. I’m looking forward to seeing it. I do hope they keep with a consistent design language to build a signature look for the city. The few renderings that are available don’t show this, however. When it comes to aesthetics, I’ll have to assign the entire project a grade of Incomplete because I just don’t know enough to make an assessment yet. But as I said, what I’ve seen makes me hopeful.
I’ll cover the interchanges north to south. The project starts just south of 56th St. but does not include that interchange. The 46th St. bridge is being replaced. The first interchange you come to is 38th St. The existing interchange is a diamond with one loop ramp. Here is the target configuration. Click for a higher resolution version. Note that INDOT’s web side for the project has super-high res images if you want to see them. Those are useful for reviewing fine detail.
Note the partial cloverleaf design. This is INDOT’s new favored design. Traffic exiting the freeway must stop at a signal on 38th. Traffic onto the freeway is free flowing in all directions. This does lead to stop lights, but with the benefit of eliminating weaving traffic on the freeway. This is a high capacity design. While it doesn’t look that different from today, I think it will be an improvement. Grade: A-
By the way, this rendering shows what I mean by an 8+2 design. There are four mainline lanes, but there is an extra auxiliary lane between interchanges as the onramp for one interchange continues through to be the offramp of the next interchange. This gives traffic plenty of time to merge in and out, without tight weaving distances.
Moving south, the 34th St. bridge will be replaced. Then comes perhaps the most complex interchange jumble on all of I-465. I-74 comes in from the west as a freeway, then while I-74 is routed as a multiplex around the south side of I-465, the roadway continues straight towards the Speedway as Crawfordsville Rd. The US 136 portion of Crawfordsville, which extends beyond I-465 and parallels I-74, crosses under I-465 and comes into a signalized intersection at High School Rd. The current interchange is a full cloverleaf, with that very closely spaced signal at High School Rd. What’s more, while traffic has currently been modest on I-74, with big growth in Brownsburg and even Pittsboro, along with a new interchange on I-74 at Ronald Reagan Parkway, traffic looks set to significantly grow.
So what was INDOT to do? A partial cloverleaf is not an option here. This is a freeway-freeway interchange, so stoplights are not acceptable. The solution they came up with is one of the best I’ve ever seen. I’m not sure if this has been done elsewhere, but it is not a standard design and since I’m not aware of someplace else it exists, I’m going to give INDOT the benefit of the doubt on being innovative here. Here’s the rendering:
This is a little tough to decipher at first, but let me tell you want is going on. I-74 and Crawfordsville are no long through routed. You can see the old Crawfordsville in the photo and the new Crawfordsville in yellow. So now Crawfordsville is a through route under I-465, and I-74 effectivenely does a merge/split with I-465. This eliminates one big problem, which is the tightly spaced stoplight. Anyone coming in on I-74 no longer faces a stoplight, or any potential stoplight related backups, because you can’t get to a stoplight unless you explicitly exit to Crawfordsville.
Next, because Crawfordsville and I-74 have been separated, the interchanges have been separated. There are really two interchanges, here, with interconnected ramps. One is a simple diamond at Crawfordsville. Northbound from I-465 you easily see the separate exit ramp for Crawfordsville. Southbound from I-465, there is also a separate ramp that goes under I-74. An exit ramp from I-74 merges with this before hitting the signal at Crawfordsville. Traffic heading from Crawfordsville behaves similarly. INDOT has separated local traffic from freeway traffic while maintaining full access to Crawfordsville from all directions. This is a major accomplishment. The only downside is that the tight diamond design, which is effectively mandated by the tight spacing, will experience capacity constraints at certain peak traffic times. I’m thinking notably races at the Speedway. But apart from special events traffic, this should be adequate, depending on the volume of turn lanes, which is not explicit in this drawing. I hope INDOT makes it a fairly high capacity diamond.
With I-74 INDOT has accomplished something they’ve never done anywhere else to the best of my knowledge: they’ve completely eliminated loop ramps and other bogus features such as left hand ramps on a freeway-freeway interchange. Admittedly, this is more of a merge/split than a true freeway-freeway interchange such as I-465 and I-70, but let’s not diminish the accomplishment. This is very close to a design I previous advocated to INDOT for this interchange, namely a “four-level stack” interchange. These are expensive to build, no doubt, but they are the highest capacity design and most ROW efficient design for freeway-freeway interchanges. Here’s a picture of a true four-level stack from Houston, Texas:
The I-74 design is similar, except it has fewer directions to move traffic. Also, the ramp from inbound I-74 to northbound I-465 sweeps around like a traditional INDOT directional ramp. This avoids having to build a tall multi-level bridge structure, but the ROW was in place so they took it. INDOT also includes dual lane ramps to/from I-74 inbound and I-465 southbound, presumably the highest volume movement. This is going to move a lot of cars at high speeds through that interchange and should be a joy for motorists to drive.
I think this is one of INDOT’s best interchanges ever, and if it works as well in practice as it looks on paper, they should win some design awards for it. Grade: A+
Moving south, the 21st St. bridge will be replaced. Then comes the 10th St. interchange. Here is a rendering:
This is diamond with a single loop ramp. That weird flyover ramp and squashed loop ramp are being eliminated. The “ideal” design for this interchange is probably a partial cloverleaf like 38th. However, note the neighborhood in the northwest quadrant where the other loop ramp would go. Building it would require wiping out a good chunk of that. Plus, like 71st St. and 86th St., this is an “unbalanced” interchange, with the majority of the I-465 bound traffic coming in from the west. The westbound to southbound movement is probably lower volume. IN that light, I think INDOT did a solid job with this. Grade: B
Moving south comes Rockville Rd. This is a similar design to 10th St.
The constraint on building a second loop ramp here is less a neighborhood than the tight spacing with the High School Rd. intersection, which constrains things. This interchange also has significantly unbalanced flow as it is the primary route into the freeway from Avon and Danville. I think this one will do fine. Grade: B
The next interchange is Washington St.
With no neighborhoods, no tightly spaced intersections, and a more balanced traffic flow, INDOT was able to go with the partial cloverleaf design. I do find it interesting that they are actually making the loop ramps smaller, which should reduce their design speed. I’m not sure of the rationale for that. Grade: B+
The next interchange is Airport Expressway, soon to be renamed Sam Jones Expressway as the airport terminal is relocated to a new exit off I-70.
This one presents an interesting challenge. It is another freeway-freeway interchange, so a partial cloverleaf is not feasible. It is also the preferred route for freeway traffic to reach downtown from the north. Going all the way to I-70 takes you out of the way. Airport Expressway is a short cut spur that links to I-465 to I-70 east more directly. With the airport terminal closing, one can also expect this to become an extremely unbalanced interchange, with much less traffic to the west.
What INDOT did was to leave this mostly as it was, with three loop ramps and a flyover. There were two improvements made. One was to isolate the two loop ramps on the east side of I-465 from the mainline with a separated collector/distributor lane. This keeps the tight weaving traffic from affecting I-465 and is now the standard design when doing full cloverleaf type operations. It also re-aligned the eastbound lanes of Airport Expressway to the south. This was a nicely done move as it creates and extended weaving area for the loop ramps that should improve safety. Grade: A-
This is the last of good elements to highlight. As you can see, this is the bulk of the interchanges. In part two, I’ll cover the negative.