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Author Topic: Using tiny cloverleafs  (Read 342 times)

yand

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Using tiny cloverleafs
« on: July 04, 2019, 05:34:03 PM »

Based on my calculations, a 270 degree loop ramp with a 7% grade climbing 22ft (16ft clearance + 6ft bridge thickness) would have a minimum inner radius of 66.5ft, and a speed of 10-15mph
I have an idea for using such ramps on a tiny cloverleaf.
The interchange would be entered through CD lane with plenty of room to decelerate. Once decelerated in the CD lane, the speed limit would be 15mph, enforced by a mild speed bump maybe 40ft before the loop meets the cd lane.
Just like in a roundabout, all entering traffic must yield: Traffic on the C/D lane has to yield to loop traffic, right turning traffic has to yield to C/D lane traffic. This keeps the inner loop flowing freely even in the event of a backup.
Once right turning traffic merges into the C/D lane, then vehicles can use the long acceleration lane to get up to speed and merge.
I think such a cloverleaf would be best used on as a cheap interchange between two high speed freeways. I would much prefer a mini cloverleaf with C/D lane, right of way for the loop, and long accelerate lane. - As opposed to a medium cloverleaf that feeds low speed loop traffic directly into the mainline but has little room to accelerate. I'm guessing a mini cloverleaf with CD lane would cost about the same as a medium cloverleaf without it. There shouldn't really be much of a capacity difference of taking a longer medium loop at 25mph vs a shorter small loop at 15mph.
Thoughts?
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sprjus4

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Re: Using tiny cloverleafs
« Reply #1 on: July 04, 2019, 05:43:02 PM »

Based on my calculations, a 270 degree loop ramp with a 7% grade climbing 22ft (16ft clearance + 6ft bridge thickness) would have a minimum inner radius of 66.5ft, and a speed of 10-15mph
I have an idea for using such ramps on a tiny cloverleaf.
The interchange would be entered through CD lane with plenty of room to decelerate. Once decelerated in the CD lane, the speed limit would be 15mph, enforced by a mild speed bump maybe 40ft before the loop meets the cd lane.
Just like in a roundabout, all entering traffic must yield: Traffic on the C/D lane has to yield to loop traffic, right turning traffic has to yield to C/D lane traffic. This keeps the inner loop flowing freely even in the event of a backup.
Once right turning traffic merges into the C/D lane, then vehicles can use the long acceleration lane to get up to speed and merge.
I think such a cloverleaf would be best used on as a cheap interchange between two high speed freeways. I would much prefer a mini cloverleaf with C/D lane, right of way for the loop, and long accelerate lane. - As opposed to a medium cloverleaf that feeds low speed loop traffic directly into the mainline but has little room to accelerate. I'm guessing a mini cloverleaf with CD lane would cost about the same as a medium cloverleaf without it. There shouldn't really be much of a capacity difference of taking a longer medium loop at 25mph vs a shorter small loop at 15mph.
Thoughts?
I-85 / I-74 in High Point, NC was done like this. C/D lanes, but extremely small loop radius. The interchange opened when I-74 opened through that area in September 2011.

It still would have been nicer if they used a larger radius, especially given all the room they had, and still have the C/D lanes.

But it works nonetheless.

https://www.google.com/maps/@35.9290162,-79.9249165,905m/data=!3m1!1e3
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yand

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Re: Using tiny cloverleafs
« Reply #2 on: July 04, 2019, 06:15:49 PM »

A 140ft, 25 mph loop is pretty small but not that uncommon. I'm talking the smallest loop possible which is about half that size
Basically this https://www.google.com/maps/@19.4033637,-99.1365865,176m/data=!3m1!1e3
,but slightly bigger
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kalvado

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Re: Using tiny cloverleafs
« Reply #3 on: July 04, 2019, 06:16:49 PM »

I wonder how 7% grade would work for heavy trucks, especially in winter with snow/ice on the road..
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yand

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Re: Using tiny cloverleafs
« Reply #4 on: July 04, 2019, 07:32:39 PM »

That is a concern. What are the steepest grades allowable in northern climates?
A solution that doesn't increase the cloverleaf's overall size is to make the normal portion of the ramp wide enough to fit the entire truck+trailer, then have the right shoulder available and marked for bypassing stopped vehicles.
edit:
alternatively, we could add a road with easier slope to one of the quadrants that provides at-grade connection in event of low traction due to snow and ice, or a special/oversize/underpowered vehicle
« Last Edit: July 04, 2019, 08:18:38 PM by yand »
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jeffandnicole

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Re: Using tiny cloverleafs
« Reply #5 on: July 04, 2019, 08:53:49 PM »

I wonder how 7% grade would work for heavy trucks, especially in winter with snow/ice on the road..

I think it's 3% but not sure. I think I heard that to fit it in, the new NJ42N to 295N ramp with a slight S curve along the incline to it is going to be 5%, and they're a bit worried about it in wintertime.
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