I-415 deleted in Salt Lake City, 1969

[kurumi]

Utah DOT have hosted their 1968 application to AASHTO to extend I-215 to take over I-415 in Salt Lake City. It was approved in 1969.

http://www.dot.state.ut.us/main/uconowner.gf?n=200609121744533

I wish I could find the rest of these (all interstate applications, all states, all years :-)

[xonhulu]

Why was the southeast leg given the I-415 designation in the first place?  Did it not connect with I-215 originally because the southwest leg was built last?

[kurumi]

I don't know why there was a 415 designation. Apparently none of it was ever signed I-415: the number changed before the freeway opened.

But I found the page with resolutions (history) for more Utah state, US and Interstate routes, here:
http://www.dot.state.ut.us/main/f?p=100:pg:0::::T,V:1348,

[TheStranger]

I don't know why there was a 415 designation. Apparently none of it was ever signed I-415: the number changed before the freeway opened.

My guess would be the same rationale for the 280/680 (SF Bay Area) and 494/694 (Twin Cities) numberings - so as not to provide directional confusion when the physical road starts heading back north-south or east-west.  (280 was slated to have done the same thing with 480 as well, at the current 101/1 junction in the SF Presidio.)

[Rover_0]

If I had my way, then UT-201 (at least its freeway portions, from I-15 to I-215) would be an Interstate.  Something like I-315, I-480, or I-115 would work.  However, I don't think that at this time UT-201's freeway section isn't up to Interstate standards.  Maybe you could extend it all the way along to UT-201's western end at I-80.