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Old 01-09-2014, 06:28 PM
 
410 posts, read 388,981 times
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Highlights:
  • Major intersections spaced 1.5 miles apart and have a speed limit of 45 mph.
  • Town Center Intersections (TCIs) would be used exclusively at major intersections.
  • Mid-block intersections spaced 0.75 miles apart.
  • Michigan Lefts common at mid-block intersections.
  • Major arterials would include wide medians, allowing for more flexible innovative intersection designs (such as the superstreet).
  • Diagonal streets would be limited access and have a speed limit of 60 mph to maintain good dual progression.
  • The grid could achieve dual progression at cycle lengths of 120 seconds (high cycle length) and 60 seconds (low cycle length).
The Town Center Intersection (TCI) would be a key feature of the grid. It has greater capacity then a conventional 4-phase signal as seen in the Synchro models below (both models have the same traffic volumes). In addition, pedestrian crossing lengths are reduced at the TCI.


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Old 01-10-2014, 03:22 PM
 
410 posts, read 388,981 times
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Here's a good example of a Town Center Intersection. It's not hard to imagine the development opportunities that such an intersection provides.

https://maps.google.com/?ll=33.09823...04823&t=h&z=18
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Old 01-10-2014, 03:49 PM
 
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I suppose there may be some pluses to this from a traffic engineering / vehicle throughput scenario but frankly the scale of these roads are just hideous and if there really is that much traffic whizzing past I can't imagine it is going to be pleasant for anyone to live close to these roadways, let alone walk near them or heaven forbid anyone attempt to ride a bicycle on them...

I far from the biggest advocate of making accomodations for people on two wheels / hoofing it but these seem to really invite horribly anti-pedestrian scale developments with island that are also impossible to foresee anyone riding a bicycle on the approaching roadways...
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Old 01-10-2014, 06:22 PM
 
410 posts, read 388,981 times
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Here's an example of a major suburban intersection (Kirkman Rd. & Conroy Rd. in Orlando):


Converting this intersection to a Town Center Intersection would have a couple major advantages:

1. Pedestrian crossing lengths would be reduced. Pedestrians wouldn't have to walk across 9 lanes of traffic to cross the street.

2. Left-turn phases would be eliminated. This greatly increases vehicle capacity (as seen in the SYCHRO models). Also, many studies have found that innovative intersections reduce injury accidents.
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Old 01-10-2014, 09:30 PM
 
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The amount of space required for the so-called Town Center intersection is ridiculously large; basically you turn your two-way street into two one-ways at each intersection.
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Old 01-10-2014, 11:41 PM
 
410 posts, read 388,981 times
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Quote:
Originally Posted by nybbler View Post
The amount of space required for the so-called Town Center intersection is ridiculously large; basically you turn your two-way street into two one-ways at each intersection.
You get the mobility of a two-way street and the capacity of two one-ways. A Town Center Intersection increases capacity which helps promote development (higher density). High density urban centers often have a tight grid of one-way streets. If you had to choose, what suburban intersection option would you prefer?

Option A: Conventional 4-phase intersection

https://maps.google.com/?ll=28.49395...00862&t=h&z=20

Option B: Town Center Intersection

https://maps.google.com/?ll=33.09823...04823&t=h&z=18

https://maps.google.com/?ll=39.760127,-104.890554&spn=0.001645,0.001725&t=h&z=19
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Old 01-11-2014, 07:18 AM
 
Location: Michigan
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I actually think the TCIs are too small to really be effective, in this case. In suburban development, you'd really have to plan out the whole community around the intersections otherwise traffic will simply flow right through them. I noticed in your 1st picture of option B example, the rest of the area is built in typical suburban tracts which defeats the purpose of creating a walkable non-autocentric neighborhood.

In other words, it's becomes an aesthetic rather than a functional way of developing a suburban area. Which is the feeling I get from the 2nd picture of your option B. It looks pretty, but it doesn't seem any less autocentric than the usual 4-phase intersection.

TCI's don't seem like a bad idea in it of themselves, but if the idea is to create density and mobility then essentially you're going to end up recreating suburbs that look like the examples below.

It's very common in many cities that have the old (and sometimes newer) highway system leading into their downtowns to split into two way roads and traverse the length of the city or downtown area. In most cases the highways simply aligned with roads already existing in the grid. However, the traffic pretty much flows similar to how it would in a TCI.





An extreme example.



I'd imagine that if you made TCIs large enough to build a grid within and around them, then I could see that developing into a dense walkable area. Otherwise, it seems like just aesthetically better looking suburbs.
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Old 01-11-2014, 09:32 AM
 
410 posts, read 388,981 times
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Many suburbs are already low-density and autocentric. Constructing TCI's at major suburban intersection isn't an attempt to transform a suburb into an urban center. However, TCI's would promote greater development (to a point) because of the increased capacity the intersection provides. The TCI is not just aesthetic as it increases capacity and reduce pedestrian crossing distances (the pedestrians who cross the suburban intersection wouldn't have to walk across 9 lanes of traffic anymore).

This grid is an attempt to improve on the suburban experience for the cul-de-sac dwellers out there.
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Old 01-11-2014, 11:54 AM
 
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Your Options A and B aren't similar because the total road sizes are different; the Town Center Interchange only totals about half the lanes of the conventional one. And it's chopping up the land into those 5 oddly-shaped not very usable spaces. Option A is a monstrosity, but at least it's compact. If pedestrian access is an issue, pedestrian bridges are a possibility, though since it looks like it's a suburban commercial area, pedestrians are probably few and far between anyway.
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Old 01-12-2014, 12:21 PM
 
410 posts, read 388,981 times
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Quote:
Originally Posted by nybbler View Post
Your Options A and B aren't similar because the total road sizes are different; the Town Center Interchange only totals about half the lanes of the conventional one.
The second TCI pictured in Option B has 1 less through lane than the Option A example. There is a big different is the number of left-turn lanes though. The Orlando intersection has double left-turn lanes at all 4-legs of the intersection where the TCI doesn't require the same amount of left-turn lane storage (left-turn phases are completely eliminated at the TCI and there is no conflicts with someone wanting to turn left).

Quote:
Originally Posted by nybbler View Post
And it's chopping up the land into those 5 oddly-shaped not very usable spaces.
Looking at the first TCI example they developed town houses, a cafe, a gas station, and a large park within the 5 parcels. Consider the gas station developments at the corner of the Orlando intersection to the one at the TCI. For the TCI, regardless of what direction you are traveling on San Elijo Road, there is easy access to the gas station. For the Orlando intersection, if you are traveling NB Kirkway, the only way to access the gas station is by making a U-turn:





In some ways, the center parcels formed by a TCI are more useable than the parcels at a conventional intersection. I admit that the second Option B example isn't large enough for meaningful commercial develop within the median. However, it's the smallest TCI intersection i'm aware of in America, with most TCI's having much wider medians. Ideally, the TCI would be large enough for development, but not so large that it would negatively effect signal progression along the arterial (the farther the intersections are apart, the worse progression becomes).

Quote:
Originally Posted by nybbler View Post
If pedestrian access is an issue, pedestrian bridges are a possibility, though since it looks like it's a suburban commercial area, pedestrians are probably few and far between anyway.
Town Center Intersections would be a great way to reduce continuous pedestrian crossing lengths at large suburban intersection. Pedestrians crossing the south leg of the Orlando intersection have a 180 foot hike across the street. Converting the intersection to a TCI could easily reduce that crossing length by over 100 feet.
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