T-Interchanges: Best bang for the buck

[Occidental Tourist]

What type of T interchange provides the most traffic capacity for the relative cost?  Directional T's are great for speed, ramp curvature and throughput but require significant costs in that they need a lot of land for a two-level setup or they need a three-level setup.

Semi directional T's allow a smaller footprint but sacrifice ramp speed.  Trumpets can take up even less land but ramp curvatures tend to require traffic to slow significantly.

Then there are more uncommon configurations like parclo T's and semi-directional T's that are braided.

[sparker]

What type of T interchange provides the most traffic capacity for the relative cost?  Directional T's are great for speed, ramp curvature and throughput but require significant costs in that they need a lot of land for a two-level setup or they need a three-level setup.

Semi directional T's allow a smaller footprint but sacrifice ramp speed.  Trumpets can take up even less land but ramp curvatures tend to require traffic to slow significantly.

Then there are more uncommon configurations like parclo T's and semi-directional T's that are braided.

Trumpets, particularly those that employ a single bridge covering both directions of the terminating facility, are the most cost-effective -- but the single loop employed invariably requires lower speeds to negotiate it.  Thus a trumpet may not be appropriate for interchanges where traffic to and from the terminating freeway is distributed equally in both directions of the through freeway.  An example of this is the Barstow, CA interchange between I-15 and CA 58, a trumpet with CA 58's eastern terminus there.  The "direct" ramp, from CA 58 east to I-15 north (and with the I-40 "split" a couple of miles in that direction) is configured to allow a constant 50mph around a sweeping curve; the connection from I-15 SB to CA 58 west also employs a 50mph design curved ramp.  The contrary movement from I-15 NB to CA 58 west uses the loop inside the EB 58>NB 15 ramp; it's signed for 40mph -- relatively high for a trumpet loop, but it features a large radius.  When designing the interchange in the mid-'90's, D8 reasoned that most traffic coming north on I-15 would be using US 395 from Hesperia to Kramer Jct., so the volume of traffic on the trumpet loop would be lessened considerably (likewise the direct 58E>15S ramp in the opposite direction).  The trumpet is more than adequate to handle the traffic volume, even though that is dominated by large trucks.

When the CA 58 freeway is eventually extended to I-5, the interchange of choice will likely be a trumpet, with the direct ramp handling the SB 5>EB 58 movement.  Since there's an angle somewhere around 135 degrees involved due to the diagonal trajectories of both routes, and there's available land for that type of interchange, the trumpet option would be the least costly free-flow design.   Fortunately, the presence of CA 99 as a facility that would handle most of the opposing movement (WB 58> Los Angeles) means the trumpet loop need not be designed for speeds greater than 30 mph -- in fact, if D6 wanted to "cheap out", that movement, as well as the opposing NB 5>EB 58 could be eliminated and a simple semi-directional ramp installed. 

[froggie]

There's another T-style interchange design to consider (which I am not sure the name of).  Similar to a trumpet but laid out in such a way as to avoid left-side exits or entrances.  The "loop" can also have a slightly higher design speed than a comparable trumpet without increasing the right-of-way.

For T-interchanges at roads that are not necessarily freeway, there's a type that MnDOT calls the High-T Interchange that can be squeezed into tight right-of-way situations.  Another advantage is that there is only a single 2-phase signal needed.  One downside of this configuration is the left-side exit and entrance in one direction of the main highway.

[hobsini2]

There's another T-style interchange design to consider (which I am not sure the name of).  Similar to a trumpet but laid out in such a way as to avoid left-side exits or entrances.  The "loop" can also have a slightly higher design speed than a comparable trumpet without increasing the right-of-way.

For T-interchanges at roads that are not necessarily freeway, there's a type that MnDOT calls the High-T Interchange that can be squeezed into tight right-of-way situations.  Another advantage is that there is only a single 2-phase signal needed.  One downside of this configuration is the left-side exit and entrance in one direction of the main highway.

I have always like the one used for Huron Blvd at I-94.
https://www.google.com/maps/@44.9679296,-93.2248557,818m/data=!3m1!1e3
Small footprint and can have higher speeds.

[Occidental Tourist]

I have always like the one used for Huron Blvd at I-94.
https://www.google.com/maps/@44.9679296,-93.2248557,818m/data=!3m1!1e3
Small footprint and can have higher speeds.

That's a rare one, but one of my favorite designs.

[NoGoodNamesAvailable]

I have always like the one used for Huron Blvd at I-94.
https://www.google.com/maps/@44.9679296,-93.2248557,818m/data=!3m1!1e3
Small footprint and can have higher speeds.

That is the most poorly thought-out bus stop I've ever seen. It's in the middle of a freeway interchange with no connecting sidewalks. Even if it's a transfer stop, what if your connecting bus was late or the trip got cancelled? Then you're stranded

[sparker]

I have always like the one used for Huron Blvd at I-94.
https://www.google.com/maps/@44.9679296,-93.2248557,818m/data=!3m1!1e3
Small footprint and can have higher speeds.

That's a rare one, but one of my favorite designs.

Nice innovative design, particularly in an urban setting where property acquisition is at a premium, but as a general design might not be transportable to higher-speed rural settings -- simply because standard directional or semi-directional interchanges perform the same function and have the intrinsic capability of high-speed ramps, whereas the Huron design would require quite a bit of room to achieve curvature radii capable of handling 60mph+ movements.

[thspfc]

The Minecraft world I've been working on for over a year has several T-interchanges. Two trumpets, two semi-directional T's, and two directional T's. There are at least one or two more in the works.