Redundant Interchanges

[CtrlAltDel]

The infamous extra-toll exit to I-295 from I-95 just south of Portland, Maine, seems redundant with the next exit to the north, the trumpet:



Or at least, it used to be. That northern trumpet exit looks like it's currently under construction to be turned into a diamond.

[froggie]

^ Correct.  The diamond is now open, though construction will not wrap up for another month or two.

[tmoore952]

i suspect that many of these cases involve interchanges that have been upgraded in some way.

Two possibilities I can think of are -- older interstates that were built in sections where there are redundant ramps at what used to be a termination point -- the second ramp was built to eliminate weaving or make the movement easier. I wonder if that was the case for US 29 NB at I-70 (if I-70 ended here at some point in the '60s or early '70s). Or maybe US 29 itself since I'm not sure if the part from I-70 north to MD 99 was built at the same time as the part from US 40 to I-70.

Or -- the intersecting highway itself was majorly upgraded and the existing ramp wasn't good enough anymore. Thinking here of Delaware 7 interchange with I-95 which later became Delaware 1. The old Delaware 7 ramp (which also had a ramp coming into it from Christiana Mall) to I-95 NB wouldn't work for Delaware 1, but was still needed anyway.

A third example I can think of is also an interchange upgrade -- I-370 EB (Maryland) at Shady Grove Rd where there are now two ways to get to Shady Grove Road. One is via the former 370 which is the road that goes to the Shady Grove Metro Station. The other EB ramp was built when MD 200 was built to connect to I-370 (I think the original EB ramp mentioned above was inaccessible (or at least majorly compromised) for a while while they built that new interchange). WB on MD 200 there is only one ramp to get to Shady Grove Road, and that way did not exist before MD 200 was built.

[davewiecking]

I-70/US-29 was mostly built at one time. If you're not familiar with historicaerials.com, you could probably waste the rest of your day doing "research" . I-370/Shady Grove/MD-200 design changed significantly from the first proposal; the 2 lane loop ramp movement was originally designed as a flyover ramp. As you note there's no duplication of ramps coming from the east, and it seemed to me they just added asphalt on the fly to spread out the traffic onto Shady Grove.

[roadman65]

Exits 2B and 2C on I-80 in SF both serve Fremont Street.

I believe this may have to do with removing the Embarcadero Freeway and its interchange with I-80, but still only need one ramp for Fremont Street.