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SPUIs - Single Point Urban Interchanges

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Here's what Houston's freeways and street interchanges are missing: SPUIs. Like a freeway-to-freeway interchange, you don't have to wait at a light on the access road, but cut across to the left at 45 degrees to make a turn at a light on top of the middle of the freeway. And it would alleviate traffic unlike the regular cross street intersections. They have this in cities like Tulsa, Las Vegas and Phoenix right now.

It would've worked on I-10 west of Highway 6 to Katy and Highway 59 north of Beltway 8 near IAH and I-45 North of the Beltway where they used to underpass the streets. But too bad this is another idea ppl will miss out on because TxDot converted them underpasses to overpasses. :angry2:

Image Sources: Wikipedia article: SPUI



And cause of the frontage road turnaround configuration and poor sight vision due to the bridge hump walls, this is highly unlikely:


Drop your thoughts.

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SPUI's are a fantastically efficient design (in terms of traffic operations) for diamond interchanges.

The major problem with them is that you cannot place bridge piers in the median because your left-turn vehicles from the ramps are using the median for their turns. Because of this, they are structurally expensive to build.

One reason why they won't work on Houston's existing freeways is our system of frontage roads. The freeway system is set up for people to be able to travel continuously down the frontage roads, and that is impossible in a SPUI, as exiting traffic must turn right or left. It is intended for freeways without frontage roads.

However, for a new freeway in Houston that would be designed without frontage roads, I'd be all for SPUI's.

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unfortunately this design doesnt take into account accessing all of the businesses we have on the feeders. The freeway portion shown has no feeders. The familiar design now used here has evolved over the years, including the supposedly revolutionary U-turn lane without having to go through a light.

Edited by musicman
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The old US 99@I-10 interchange used to be very similar to this. They tore it down a few years ago, of course.

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What am I missing about this intersection design that supposedly makes them so much more efficient? I'm just seeing a different location for the traffic light.

Unlike a traditional diamond interchange, only one signal controls traffic at the SPUI. There are only three phases for this signal:

1 - Left turns from the off-ramps

2 - Left turns from the signalized roadway

3 - Through traffic on the signalized roadway

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