Svo voru nokkrar aðrar breytingar sem ég þorði sjálfur ekki að setja í gegn, t.d. 40 km/klst hámarkshraði á Hvaleyrarvatnsvegi, sem skv. listanum ætti að hafa 50 km/klst hámarkshraða en skv. götumyndum á ja.is og fyrri "töggum" er skiltaður með 30 km/klst hámarkshraða.

Var búinn að fara sjálfur í gegnum listann hjá Hafnarfjarðarbæ (https://hafnarfjordur.is/umferdarhradi-laekkadur-i-hafnarfirdi/)
Miðað við listann í Stjórnartíðindum eru einhverjar villur sem finna má í þessum breytingum (https://www.stjornartidindi.is/Advert.aspx?RecordID=69ed044a-8f69-4b24-8bc8-9f2592c7a601)
Tek t.d. að einungis er lækkaður hámarkshraði á Kaldárselsvegi frá Elliðavatnsvegi að Kaldárseli. Ætti því ekki að haldast 50km/klst hámarkshraði við Kaldárselsveg milli Elliðársvatnsveg og Ásbrautar?

Changed on a legal level "city wide" that is to say

The street level imagery on ja.is is from summer 2022. In an announcement from Kópavogsbær March 2024 speed limits were reduced on almost all streets in Kópavogur. https://www.kopavogur.is/is/frettir-tilkynningar/breytingar-a-hamarkshrada
I've personally not surveyed whether they've updated the signage in Digranes but in Fífuhvammur and Vatnsendi these changes have already taken effect on a street level (on a legal level these changes have already taken effect, see https://www.stjornartidindi.is/Advert.aspx?RecordID=85a3c6b0-255c-40de-9288-8c46f8d7b870).

The Icelandic Highway Authority (Vegagerðin) classifies all its roads into different hierarchical groups;
Stofnvegur (S) - literally translated to main road, i.e., primary road or trunk way (route 1),
Stofnvegur um hálendi (Sx) - main road over the highlands,
Tengivegur (T) - connecting road, i.e., secondary road,
Héraðsvegur (H) - county road, and
Landsvegur (L) - country road, often used for all other roads that don't fit in the aforementioned categories.

The road classifications can be found in Vegaskrá, which is a public document and can be used according to osm.wiki/Iceland .
In Vegaskrá you can find the classification under "Vegflokkur".

I don't really know why designation is used. According to osm.wiki/Is:Map_Features , the tag "network" should be used to indicate the road classification. I have simply been following convention seen on other roads.

I'm fairly sure these restrictions do no apply to Akrafjallsvegur itself. Looking at the signs near the intersection of Akrafjallsvegur and Akranesvegur (https://ja.is/kort/?x=353234&y=428738&nz=13.52&ja360=1&jh=116.7) they all have a sign below stating an exception to the upper sign e.g. "No horses (upper sign) - í Hvalfjarðargöngum (lower sign)", meaning that the restriction only applies in the Hvalfjörður tunnel.

The name of this road is also Kambavegur on older plans, see deiliskipulag from 2007 below. While it is called Turnahvarf on the street sign, I decided to change the name in line with construction of a residential neighbourhood SE of Turnahvarf.
Deiliskipulag 2007: http://skipulagsaaetlanir.skipulagsstofnun.is/skipulagvefur/DisplayDoc.aspx?itemid=02634425796859637500

I recently merged both segments in line with deiliskipulag (local plan) from 2023, see:
http://skipulagsaaetlanir.skipulagsstofnun.is/skipulagvefur/DisplayDoc.aspx?itemid=Y_SWt5_Fq0mJvh7YYukbEA
and
http://skipulagsaaetlanir.skipulagsstofnun.is/skipulagvefur/DisplayDoc.aspx?itemid=ny8ZhRy4AUC1OGuiBLA_Q

*Ölkelduvegur

*147899600

I was debating whether it should count as regional or local. I went with local since it's only on the agenda at Akureyrarbær, as opposed to the system in the capital (signed by most if not all municipalities there).

Source: https://straeto.is/skipuleggja-ferd/timatoflur/landsbyggdin

*Álftanes

Source: https://www.utu.is/wp-content/uploads/2023/07/8b.-Sunnuhlid_endursk.dsk_.-uppdr.pdf

Unsure whether the road has been opened to the public but it's been paved recently.

Second source, https://fundur.reykjavik.is/sites/default/files/agenda-items/Tillaga%20Einstefna%20Bjarkarg%C3%B6tu%20og%20Tjarnarg%C3%B6tu.pdf

Here is the full report available to the public,
http://skipulagsaaetlanir.skipulagsstofnun.is/skipulagvefur/DisplayDoc.aspx?itemid=stnL2UGLtk6526dPzIEXPg

The boundary for the residential development extends between Einarsnes, Hangar 3, and Fáfnisnes.
Here are the full plans for the first expansion, http://skipulagsaaetlanir.skipulagsstofnun.is/skipulagvefur/DisplayDoc.aspx?itemid=CknYhOnsfEe0g6Wit8jaDg

Building no. 11 in the plan, south of Fáfnisnes, is a planned school building, not a house.

*Byggðastofnun, ekki byggðarstofnun

Seems like there is supposed to be a connection for bikes and pedestrians near the roundabout over to Grenivíkurvegur according to bid documents (útboðsgögn). Just open the image on the bottom of this page and zoom in: https://www.svalbardsstrond.is/is/mannlifid/frettir/gongu-og-hjolastigur-i-vadlaheidi