Why are these ramps the way they are?

[cjk374]

I-20 in Louisiana has some ramp layouts that I don't understand why they were poured onto the ground the way they were.  But some layouts I do.  Here is one I understand:

https://www.google.com/maps/@32.4569528,-91.7599988,18z

This is exit 138 at Rayville.  All of the ramps are on the west side of LA 137, er uhhh US 425 now because at the time when I-20 was being built, the Missouri Pacific RR had a branchline that ran through Rayville.  The line was removed many years ago.  In fact, when LA 15 south of Rayville was widened to 4-lane divided, the RR ROW was used for the north bound lanes.

Here is another setup I understand:  https://www.google.com/maps/@32.3298557,-91.02233,17z

This is exit 182 at Mound.  Obviously, there is a body of water and swampy area on the west side of LA 602.  Just easier & smarter to build ramps on dry land.

Now the setups I don't understand.  The first 2 are the same design and 4 miles apart:  https://www.google.com/maps/@32.538922,-92.7501876,14z

Exit 77 (Simsboro) and exit 81 (Grambling) both have 270-300 degree exit ramps on the west bound side.  The only reason I can come up with is that the state highways at both exits only run south from I-20 and parish roads go north.  If that is the official reason, I don't know.

The other 2 that confuse me:

https://www.google.com/maps/@32.563683,-93.0537171,17z

https://www.google.com/maps/@32.5379669,-92.5096972,17z

In both cases, there are 2 on ramps for westbound traffic.  Both state highways are 2 lane.  Why the extra ramps?  Beats me. 

[roadman65]

What is the topography of the area?  Perhaps it might be because of the land that they are that way.

[Stratuscaster]

For exits 77 & 81, it looks to me like that was where space was available.

My initial thought on the other two was so that traffic wouldn't have to deal with crossing oncoming traffic, but that doesn't explain why the south side ramps do have to deal with it.

[johndoe]

Loop ramps are often used because they convert left-turns to right-turns, which generally don't require extra turn lanes or traffic signals.

[cjk374]

What is the topography of the area?  Perhaps it might be because of the land that they are that way.

After some thinking, for Gibsland and Choudrant (exits 61 & 93 respectively) I-20 west bound goes up a long hill as you go up the on ramps...that is starting to make sense now. 

For exits 77 & 81, it looks to me like that was where space was available.

My initial thought on the other two was so that traffic wouldn't have to deal with crossing oncoming traffic, but that doesn't explain why the south side ramps do have to deal with it.

The loop ramp at Grambling is longer and not as sharp as Simsboro.  There is a hotel at the northeast corner of the Grambling exit, but I am gonna guess that the interstate came before the hotel.  Other than that, I think I see plenty of land to have built a "regular" off ramp there and in Simsboro.

[froggie]

Now the setups I don't understand.  The first 2 are the same design and 4 miles apart:  https://www.google.com/maps/@32.538922,-92.7501876,14z

Exit 77 (Simsboro) and exit 81 (Grambling) both have 270-300 degree exit ramps on the west bound side.  The only reason I can come up with is that the state highways at both exits only run south from I-20 and parish roads go north.  If that is the official reason, I don't know.

johndoe hinted at this, but I would suggest it's to favor traffic to the south, especially in Exit 81's case (with Grambling State right there), so that westbound 20 traffic doesn't have to make a left turn.

As for the other two, Exit 93 (the bottom one) is close enough to Ruston to suggest that they expected enough Ruston-bound traffic to use the interchange to warrant a loop ramp and not a left-turn.

[theline]

At Grambling, it looks like there is a mobile home park just northeast of the interchange. I suspect that a ramp there might have involved taking one or more of the mobile home lots. I know they are supposed to be mobile homes, but they do try to avoid taking home sites whenever possible.

[bzakharin]

https://www.google.com/maps/@39.9138176,-75.0098068,17z
NJ 70 West has two ramps to NJ 41 North. I suppose this could be a vestige of the circle that used to be there, or maybe to separate the shopping center traffic from everyone else. But in both cases, why only that particular movement?

[BrianP]

https://www.google.com/maps/@39.9138176,-75.0098068,17z
NJ 70 West has two ramps to NJ 41 North. I suppose this could be a vestige of the circle that used to be there, or maybe to separate the shopping center traffic from everyone else. But in both cases, why only that particular movement?

The jug handle is primarily for left turns to get to both southbound NJ 41 and NJ 154.

[odditude]

The advance ramp allows turns in both directions onto Kings Highway and is signed NJ 41/154. The "ramp" at the intersection allows business patrons past the first ramp to turn onto Kings Highway.

[bzakharin]

ok, but why isn't the first ramp just for NJ 41 South (and 154)?

[NE2]

ok, but why isn't the first ramp just for NJ 41 South (and 154)?

Because it's better for traffic flow if most right-turning traffic goes there?

[cjk374]

Now the setups I don't understand.  The first 2 are the same design and 4 miles apart:  https://www.google.com/maps/@32.538922,-92.7501876,14z

Exit 77 (Simsboro) and exit 81 (Grambling) both have 270-300 degree exit ramps on the west bound side.  The only reason I can come up with is that the state highways at both exits only run south from I-20 and parish roads go north.  If that is the official reason, I don't know.

johndoe hinted at this, but I would suggest it's to favor traffic to the south, especially in Exit 81's case (with Grambling State right there), so that westbound 20 traffic doesn't have to make a left turn.

As for the other two, Exit 93 (the bottom one) is close enough to Ruston to suggest that they expected enough Ruston-bound traffic to use the interchange to warrant a loop ramp and not a left-turn.

What's bad is that I have seen northbound traffic at both exit 61 & 93 turn left to go onto westbound I-20 using the non-loop on-ramp.  There is nothing to prevent traffic from doing so.

[jeffandnicole]

https://www.google.com/maps/@39.9138176,-75.0098068,17z
NJ 70 West has two ramps to NJ 41 North. I suppose this could be a vestige of the circle that used to be there, or maybe to separate the shopping center traffic from everyone else. But in both cases, why only that particular movement?

ok, but why isn't the first ramp just for NJ 41 South (and 154)?

The Ramp is the preferred movement to Rt. 41 North, based on the signage.  There's a large overhead sign at the jughandle for Rt. 41; There's no signage whatsoever for the right turn onto Rt. 41 North at the traffic light, even though the right turn channel is there for traffic to make that turn.  It's just as well: there's really no benefit to making this a very long ramp just to turn left at the end of the ramp.  Traffic can turn right here, avoiding the shopping center traffic if they turned right at the traffic light. 

(I prefer this to what they did for traffic entering Rt. 206 near the Love's truck stop in Bordentown, where there's 3 lanes dedicated for left turning traffic.  Right turns are prohibited, even though there's no harm in making the right here, and it was even permitted when the nearby Turnpike was getting widened.)

Note #1: Rt. 70 East here has the same condition.  Traffic can turn right at the light onto 154 South, or they can take the jughandle (incorporated into the local roads), left at the first intersection, then right onto 154 South.  In this case, traffic for Rt. 154 South is directed to the right turn channel at the light.

Note #2: This is also true at the former Garden State Park Circle.  Rt. 70 West to Haddonfield Rd is directed to use the jughandle (again, incorporated into the local roads).  Traffic to Haddonfield Rd. North can also go to the traffic light and turn right there.  It used to be a dedicated right turn lane, but now it's a shared thru/right turn lane.

[bzakharin]

Note #1: Rt. 70 East here has the same condition.  Traffic can turn right at the light onto 154 South, or they can take the jughandle (incorporated into the local roads), left at the first intersection, then right onto 154 South.  In this case, traffic for Rt. 154 South is directed to the right turn channel at the light.

That's not really the same thing. The jughandle would require a left turn to go right, which makes no sense. Also, all movements are necessary to allow, for example, to go from 41 north to 154 South.

[roadman65]

https://www.google.com/maps/place/Clarks+Summit,+PA+18411/@41.4806213,-75.6829254,16z/data=!4m2!3m1!1s0x89c4d804146f71f3:0x871e825be81c019c

This here is got to be the worst designed interchange around.  A triple trumpet at the northern terminus of the PA Turnpike's NE Extension.

I know that originally the NE Ext was to continue Northward and that this would have been much simpler if that had happened, but when I-81 was constructed later, I mean really, couldn't have PennDOT come up with a better plan?

[cl94]

https://www.google.com/maps/place/Clarks+Summit,+PA+18411/@41.4806213,-75.6829254,16z/data=!4m2!3m1!1s0x89c4d804146f71f3:0x871e825be81c019c

This here is got to be the worst designed interchange around.  A triple trumpet at the northern terminus of the PA Turnpike's NE Extension.

I know that originally the NE Ext was to continue Northward and that this would have been much simpler if that had happened, but when I-81 was constructed later, I mean really, couldn't have PennDOT come up with a better plan?

The trumpet at US 6 is the original NT. Toll roads and Interstates in PA almost never connect at all, let alone flow into each other. I think it had something to do with funding.

A direct connection to the north would have required a second set of toll booths and 2 long bridges for the NB ramp and the trumpet would still be needed for local access to/from US 6 and US 11. Just be glad that PennDOT even put in a Turnpike interchange that doesn't require passing through a light.