Most substantial reductions in speed limit (over time)

[kphoger]

NMSL reduced some speed limits from 75 mph to 55 mph. 

[sprjus4]

NMSL reduced some speed limits from 75 mph to 55 mph.

Wasn't there at least one example of 80 mph? Or those without a speed limit?

[kphoger]

NMSL reduced some speed limits from 75 mph to 55 mph.

Wasn't there at least one example of 80 mph? Or those without a speed limit?

I'm not aware of any 80mph highways that still existed at the time NMSL was introduced.  The turnpike here in Kansas used to be 80 mph, but I think it had already been reduced by the time NMSL took effect.

But yes, I believe Montana and maybe one other state had limit-less highways at the introduction of NMSL.  However, the difference not being numerically defined, I didn't mention it.

[roadfro]

Here's one: The McCarran Harry Reid Airport connector/tunnel in Las Vegas.

The south end of the connector is basically a short freeway (unsigned SR 171) connecting to the I-215 beltway. There is one half interchange and then you're in a tunnel going under the airport's runways. Emerging from the north end of the tunnels, you have the airport access roadways and one-way Paradise Road/Swenson Street couplet to Tropicana Avenue (originally the airport's only ingress/egress).

The SR 171 freeway segment and the tunnels were had been signed at 55mph since they had opened back in 1994, with a drop to 35mph on the north side coming to the airport access roadways. After a couple years, people realized that the airport connector could be used as a quick way to get from UNLV and the east side of the Las Vegas Strip to Henderson and points south and vice versa, so the connector also unintentionally became a commuter route--enough so that later overhead signage was added to help drivers achieve proper lane positioning for the "airport bypass".

According to this 8/16/2020 article in the Las Vegas Review-Journal (McCarran airport tunnel speed limit drops to improve safety), the speed limit was dropped to 45mph on the freeway portion and 35mph in the tunnels in early 2021, in an effort to improve safety. Apparently there were a lot of backups at times (the northbound bypass has a signal not to far north of the tunnel, which can cause backups during the am commute), and when you combine this with people treating it like a freeway, lower visibility in the tunnel, etc., it was a recipe for problems. Unexpected backups led to rear-end collisions, etc. 150 collisions over 2018-2019 alone. Apparently accidents decreased after the speed limit drop. (But from personal experience, many people are still doing 55+ through there...)

March 2020 street views: NB freeway @ 55mph, NB tunnel entrance w/ no SL sign (but this April 2015 view shows one of the small DMS signs in the tunnel reminding of the 55mph speed limit), NB airport roads at decision point w/ 35mph ahead warning

March 2021 street views: NB freeway @ 45mph, NB tunnel entrance @ 35mph, NB airport roads at decision point @ 35mph