Former four-laned roads

[Takumi]

US 301 from Jarratt, VA to just south of Petersburg, VA was four lanes, but narrowed back to 2 lanes when I-95 was constructed along side taking away the former NB lanes to become the new SB I-95 lanes.

Part of that is still four lanes, in the Carson area for about a mile.

In Petersburg, VA, Winfield Road (US 460 Business) was demoted to two lanes at some point.

[countysigns]

In western Lucas County, Ohio, Airport Highway (OH-2) went on a road diet.

http://www.dot.state.oh.us/districts/D02/RoadDiet/Pages/default.aspx

ODOT explains what it did in the link above.

[iowahighways]

The city of Des Moines in recent years has turned a few four-lane streets into three-lane streets with a center turn lane and dedicated bicycle lanes -- Ingersoll Avenue west of downtown is an example.

A four-lane divided segment of US 30 existed between Denison and Dow City, IA, from about 1960 until the late 1970s. When the DOT resurfaced the eastbound lanes at that time, they decided not to resurface the westbound lanes due to the lack of traffic. If you look at aerial photos in the area, though, the right-of-way for a four-lane highway is still there.

[busman_49]

E. Lincold Way (former US 30) from just east of Wooster east to where it becomes a divided highway was once a 4-lane, undivided road.  After the new highway was built, the old section was turned into 2 lanes with a center turn lane and wider shoulders.

[cpzilliacus]

A section of State Street through Jackson was reduced to three lanes (with a turning lane) after being decommissioned as US 51. As a four-lane, State Street was rather narrow, so I can definitely justify it being downgraded. It's the only road in the area I can think of that used to be four-laned.

Md. 144 (Old National Pike) east of Frederick crossing the Monocacy River used to be four lanes when it was U.S. 40.  The parallel section of I-70 was the last to be completed in Maryland (the freeway unceremoniously became a four-lane arterial between present-day Exits 56 and 59).

The Monocacy is a fairly large river, and one of the two large bridges that spanned its waters when the road was U.S. 40 is now abandoned.