Turbine Inspired Roundabout Interchange Without Weaving

[zzomtceo]

Many roundabout interchanges have weaving on their roundabout portion, but this design does not if you look very closely. Another benefit is the same traffic flow as turbine, stack, and windmill. The only time one exit ramp goes over another is at points where one of the ramps would be at the same elevation as the freeway it would be adjacent to, which the other ramp must go over anyways. The picture needs to be looked at closely, pay attention to the lanes on the roundabout portion, where they get on and leave the roundabout. A lane joins the roundabout as an outer lane but becomes an inner lane before getting to where it needs to merge with the freeway, because the lane that was previously the inner lane has left to merge with the freeway. Because of this the lane itself moves position in the roundabout instead of making drivers switch lanes, which would result in weaving.

[NE2]

Why not just get rid of the roundabout entirely?

[zzomtceo]

Why not just get rid of the roundabout entirely?

And how would you make a left turn if you did that?

[NE2]

Separate the ramps; there's no need to weave between them to continue around the roundabout. See the interchanges in Albany and Chicago.

[zzomtceo]

Separate the ramps; there's no need to weave between them to continue around the roundabout. See the interchanges in Albany and Chicago.

More ramps are expensive, a lane divider can be put in with the extra benefit of preventing anyone from weaving.
Edit: I think you're thinking of a turbine interchange, this is designed to be a turbine with fewer ramps (hence turbine inspired)

[froggie]

The only "roundabout interchange" that I'm aware of is at US 61/Causeway Blvd in Metairie, LA.  Not exactly an interchange type with high demand.

This appears to be the authors alternative to a stack or 4-way directional/semi-directional.  Furthermore, unless you make the roundabout portion extraordinarily wide (which in turn drives up the right-of-way requirements, there would be vertical spacing and curvature problems with the inner ramps....much tighter than the author probably thinks.

As for the latest comment that it's "designed to be a turbine with fewer ramps", there's technically 16 ramps in his design.  Last I checked, a turbine only required 8.

Ultimately looks like a solution in search of a problem.

[zzomtceo]

The only "roundabout interchange" that I'm aware of is at US 61/Causeway Blvd in Metairie, LA.  Not exactly an interchange type with high demand.

This appears to be the authors alternative to a stack or 4-way directional/semi-directional.  Furthermore, unless you make the roundabout portion extraordinarily wide (which in turn drives up the right-of-way requirements, there would be vertical spacing and curvature problems with the inner ramps....much tighter than the author probably thinks.

As for the latest comment that it's "designed to be a turbine with fewer ramps", there's technically 16 ramps in his design.  Last I checked, a turbine only required 8.

Ultimately looks like a solution in search of a problem.

Although I agree now with your comment on spacing, some of the turbines longest ramps are merged to make the roundabout, the remaining extra ramps are much smaller.

[cpzilliacus]

This appears to be the authors alternative to a stack or 4-way directional/semi-directional.  Furthermore, unless you make the roundabout portion extraordinarily wide (which in turn drives up the right-of-way requirements, there would be vertical spacing and curvature problems with the inner ramps....much tighter than the author probably thinks.

From a human factors perspective, I also think a lot of drivers would be very confused by this design.

Especially those left-side ramps "exiting" from the "roundabout."

As for the latest comment that it's "designed to be a turbine with fewer ramps", there's technically 16 ramps in his design.  Last I checked, a turbine only required 8.

Agreed.

Ultimately looks like a solution in search of a problem.

Could be.  That's way above my paygrade.

[zzomtceo]

From a human factors perspective, I also think a lot of drivers would be very confused by this design.

Especially those left-side ramps "exiting" from the "roundabout".

If there were lane dividers and you had to stay on the same lane as you entered, it shouldn't really confuse drivers, they just need to make the decision to make the exit and in what direction of the freeway they're going to. Every time another lane exits there could be another sign to reassure drivers that they're in the right spot.

[english si]

This exists in real life, at the M11/M25 junction in Essex. It's not at all confusing - in fact, it's hard to realise that the junction can be driven all the way round - it only seems to be so, on the two shorter 'weaving' sections (where you can, theoretically, change ramp), due to the lack of horizontal separation and to save money building a barrier between them.

They use cones to stop you travelling around the roundabout, as mere "do not cross" hatching wasn't good enough to dissuade.

[Brandon]

From a human factors perspective, I also think a lot of drivers would be very confused by this design.

Especially those left-side ramps "exiting" from the "roundabout".

If there were lane dividers and you had to stay on the same lane as you entered, it shouldn't really confuse drivers, they just need to make the decision to make the exit and in what direction of the freeway they're going to. Every time another lane exits there could be another sign to reassure drivers that they're in the right spot.

Why?  It's ingenious for creating a C/D lane separate from the freeways involved.  If you miss your exit, just go around until you get back to it.  It's great for forcing people to make a U-turn as well should the freeway ahead be closed for some reason.  It's like a cloverleaf without the disadvantages of a cloverleaf (weaving on the freeway itself).

[zzomtceo]

From a human factors perspective, I also think a lot of drivers would be very confused by this design.

Especially those left-side ramps "exiting" from the "roundabout".

If there were lane dividers and you had to stay on the same lane as you entered, it shouldn't really confuse drivers, they just need to make the decision to make the exit and in what direction of the freeway they're going to. Every time another lane exits there could be another sign to reassure drivers that they're in the right spot.

Why?  It's ingenious for creating a C/D lane separate from the freeways involved.  If you miss your exit, just go around until you get back to it.  It's great for forcing people to make a U-turn as well should the freeway ahead be closed for some reason.  It's like a cloverleaf without the disadvantages of a cloverleaf (weaving on the freeway itself).

While that'd create a bit of weaving on the ramp, and I specifically said that would be suboptimal due to causing confusion, I'm totally taking that as a compliment on the design.

[zzomtceo]

This exists in real life, at the M11/M25 junction in Essex. It's not at all confusing - in fact, it's hard to realise that the junction can be driven all the way round - it only seems to be so, on the two shorter 'weaving' sections (where you can, theoretically, change ramp), due to the lack of horizontal separation and to save money building a barrier between them.

They use cones to stop you travelling around the roundabout, as mere "do not cross" hatching wasn't good enough to dissuade.

That design is slightly different, but the same principle. This design is the kind of thing that looks confusing only when you step back to take a look at the whole thing. The decision patterns you make and the signs or exits you must take are identical to a cloverleaf.

[zzomtceo]

A more detailed design showing the individual lanes on the roundabout, which would be seperated, the roundabout lanes are in grey. Sorry about the bad quality but I wasn't exactly sure how to do only part of a circle in Inkscape so I drew the things with the curve tool.

[Alps]

This exists in real life, at the M11/M25 junction in Essex. It's not at all confusing - in fact, it's hard to realise that the junction can be driven all the way round - it only seems to be so, on the two shorter 'weaving' sections (where you can, theoretically, change ramp), due to the lack of horizontal separation and to save money building a barrier between them.

They use cones to stop you travelling around the roundabout, as mere "do not cross" hatching wasn't good enough to dissuade.

Why are there not more permanent barriers in place? Potential need to use in emergencies?

[Joe The Dragon]

This exists in real life, at the M11/M25 junction in Essex. It's not at all confusing - in fact, it's hard to realise that the junction can be driven all the way round - it only seems to be so, on the two shorter 'weaving' sections (where you can, theoretically, change ramp), due to the lack of horizontal separation and to save money building a barrier between them.

They use cones to stop you travelling around the roundabout, as mere "do not cross" hatching wasn't good enough to dissuade.

and that looks like it was upgraded to that not a new build out

[Brandon]

They use cones to stop you travelling around the roundabout, as mere "do not cross" hatching wasn't good enough to dissuade.

Who the hell actually pays attention to striping?

[english si]

and that looks like it was upgraded to that not a new build out

Nope - it was built like that. The M11 had a lane drop in exactly the right places (and presumably overbridges) long before the M25 came and they built the slip roads.

That design is slightly different, but the same principle.

How is it different?

The decision patterns you make and the signs or exits you must take are identical to a cloverleaf.

Actually, more like a stack. I guess if a cloverleaf had c-d lanes. Both directions of the other road leave on the same ramp, which then splits.

Why are there not more permanent barriers in place? Potential need to use in emergencies?

Certainly the police/fire/etc can use the junction to do a u-turn on either motorway, which is a useful thing to have, given relatively long distances to nearby junctions. But that doesn't explain the design - other junctions have police-only slips to do it.

Also perhaps cost, space, or something. The hatched areas are, at best, the width of the hard shoulder. Perhaps there aren't barriers as the designer liked to experiment and create such a junction - similar to the OP.

Who the hell actually pays attention to striping?

Apparently British people - at least in the minds of transport planners. Many a straight rural road has had 2 foot of hatching drawn down the middle (with permissive broken lines) to stop overtaking.