Reddit mentions of TMS Mass Loaded Vinyl 4' X 10' (40 sf) 1 Lb MLV Soundproofing Barrier. Highest Quality!

They will do very little; the blocked sound will simply "go around" the mats.

If you really want to block noise, pick up some MLV and lay a contiguous (overlap and tape seams) layer over the entire floor.

Source: http://www.sounddeadenershowdown.com/how-to/seal-seams-mass-loaded-vinyl

Oh! If that's the case, then cement board isn't gonna do anything for you. What you'd want for effective sound dampening is pickets on both sides (staggered relative to the opposite ones) with a product called mass loaded vinyl in between. It's not the cheapest stuff, but it's the appropriate product for what you want to achieve. You also want height on the fence. 8 feet minimum for sound dampening. I (and I think other posters) got the impression you were building a tile barrier.

Thick landscaping elements can also help, to a degree. Arborvitae, for example, are dense and evergreen. Their foliage serves to scatter and absorb sound. But don't put money into cement board for sound dampening - it's not gonna do the job.

MLV: https://www.amazon.com/gp/product/B008JHE1P6/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

CCF: https://www.amazon.com/gp/product/B00URV8MFC/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

CLD: https://www.amazon.com/gp/product/B01BKKZ1AM/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

I've used various CLD's in the past (you can see some Dynamat Extreme on my front door). I figured the Noico would work well and it seems to have done well so far.

I did see a review on Amazon about the CCF glue delaminating when applied directly to the MLV, so I elected to use it on the door panel directly to keep the glue away from the MLV.

TMS Mass Loaded Vinyl 4' X 10' 40 Square Feet 1 Lb MLV Acoustic Barrier

$120 for 40ft^2

https://www.amazon.com/Loaded-Soundproofing-Barrier-Highest-Quality/dp/B008JHE1P6/ref=sr_1_3?keywords=MLV&qid=1563051341&s=gateway&sr=8-3

I bought MLV from Amazon with free shipping. Used other materials from SDS and used his method. Bought TMS MLV. No issues with smell. It was easy enough to work with.

https://www.amazon.com/gp/aw/d/B008JHE1P6?psc=1&ref=ppx_pop_mob_b_pd_title

There’s this rubber stuff they use in cars that you can lay under the carpets. It’s on amazon at a decent price for a roll.

Here ya go
TMS Mass Loaded Vinyl 4' X 10' (40 Square Feet) 1 Lb MLV Acoustic Barrier https://www.amazon.com/dp/B008JHE1P6/ref=cm_sw_r_sms_c_api_qPkTAb2CC9FSY

I might.

One idea is to use a layer of mass loaded vinyl, sandwich it between two blankets, and sew like a quilt. If the vinyl isn't flexible enough already, cutting a pattern of slices before sandwiching will make it more flexible.

40 sq ft (4' X 10' ) costs about $120 on Amazon It's density is 1lb/sq ft.

The other option that came to mind is the nuclear option, it's much more expensive for a smaller blanket. A 2'X4' lead protective blanket is about $225, has a density of 1.6 lb/sq ft, and has the added benefit of shielding you from radiation. But that's not nearly a queen size blanket.

If the internet is right and a queen blanket is 90" X 90", 56.25 sq ft, the mass loaded vinyl option seems to be your best bet. You could use just the 40 sq ft and make a blanket with a "sweet spot" in the middle, or if you want full a full 56 sq ft of super- heavy, buy a larger roll.

And then there's companies like this that sell weighted blankets pre-made.

Of course, none of these options are terribly affordable.

This seems reasonable, should be enough for a car.