It's pronounced "spoo-ee"

SPUI diagram

It all makes sense when you look at the diagram. Sort of.

As Fred highlighted this morning, the new Rt 7 bridge over the Northway in Latham will feature a single-point urban interchange or SPUI.

A what?

The current interchange at the Rt 7 bridge is what's called a diamond interchange. (Go have a look at a satellite picture of the spot.) The diamond is built around two sets of traffic lights, one on each side of the interstate. Even though it's called a diamond, the heart of the layout resembles a rectangle.

Well, a SPUI is like a diamond, but that rectangle at the heart is squished into something closer to a square. And at the middle of the square is a single set of traffic lights. Yep, one set of signals for the whole interchange -- it's the "single-point" in single-point urban interchange. Check out this video diagram of one from the Missouri Department of Transportation.

There's a good Wikipiedia entry about SPUIs that lists the layout's advantages and disadvantages. The short story:

good
+ SPUIs are reportedly more efficient at moving vehicles through an interchange.
+ Crashes that occur inside them tend to be less severe

bad
+ They can cost a bit more to construct.
+ Clearing snow from them can be difficult. In some cases, the interchange has to be closed to get it clear.
+ They can be hard for cyclists and pedestrians to get through.
+ Research also indicates that a SPUI's overlapping lane lines can be confusing to people who have never seen them before (there's anecdotal evidence, too).

So, start studying. You have a few years to get caught up. The SPUI on Rt 7 isn't scheduled to be finished until 2011.

(Thanks, Fred!)

image: Wikipedia

Find It

Rt 7 and I-87

Latham, NY 12110

Comments

That spoo-ee looks like my tattoo!

Why am I not surprised that the state would choose to build an intersection that is even less bike and pedestrian friendly than the one there currently? Shouldn't we be encouraging people to use non-oil powered transportation? Just one more example of government's short-sightedness.

A similar intersection was created on Long Island years ago: http://tinyurl.com/6rw62l - and created a much improved intersection between a commuter highway and a busy commercial road. The intersection did not originally include an overpass for the highway, so this design greatly improved traffic flow. Still I find it much nicer and there being a much less wait to turn left onto either road.

No no no no no no! This is not the most efficient way to do things. Didn't Latham officials receive the blueprints I sent them? It was scribbled on the back of a cocktail napkin and left on the steps of city hall. I even drew a smiley face on the opposite side in case there was any confusion. Why do I even bother.

Amen to the new design. The current design's traffic-light timing requires left turning cars to sit in the center turn lanes for at least half of a complete signal cycle. No wonder traffic is slow.

If you'll excuse the outright URL pimping, my good friend Bill records a podcast on traffic issues called, appropriately, Talking Traffic. Go listen, it's very interesting and informative. Maybe I can get him to do an episode on SPUIs?

You know, they conquered this whole problem in Europe a few decades ago with a traffic control device we are only just now starting to adopt. The traffic circle requires no lights, no interruption in traffic flow, and is thus more fuel efficient.

It does however require one thing that Americans don't seem to be very good at. Courtesy and it's close relation, recognition of right of way.

Interesting - I agree with the comment made by komradebob - the traffic circle can really work. I've even seen traffic circles with traffic lights too.

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