Ohio State Route 4

State Route 4 (SR 4), formerly known as Inter-county Highway 4 until 1921 and State Highway 4 in 1922, is a major north–south state highway in Ohio. It is the fifth longest state route in Ohio. Its southern terminus is at U.S. Route 42 in Cincinnati, Ohio, and its northern terminus is at U.S. Route 6 in Sandusky, Ohio. Its path is nearly ruler-straight for many miles. Some portions of the route are still marked as Dixie Highway. The northern portion was constructed by the Columbus and Sandusky Turnpike Company, see Turnpike Lands.

The portion from Cincinnati to Dayton primarily consists of arterial roads. State Route 4 begins at an intersection with U.S. Route 42 in the North Avondale neighborhood of Cincinnati. Initially called Paddock Road, it runs concurrently with Vine Street in northern Cincinnati, and then Springfield Pike as it passes through suburban northern Hamilton County. Upon crossing into Butler County, it curves to the west to pass near the downtowns of Fairfield and Hamilton, while Route 4 Bypass takes a more direct route.

The portion of SR 4 between High Street (SR 129) and North Fair Avenue in Hamilton is designated as the "Firefighter/Paramedic Patrick Wolterman Memorial Highway", in honor of a firefighter/paramedic for that city who died December 28, 2015, while battling an intentionally-set house fire. The two men who started the blaze were convicted of murder and arson in November 2017 and sentenced to life in prison. This portion of SR 4 passes by Wolterman's fire station.

From Hamilton to Dayton, the road roughly follows the Great Miami River. It turns northeast to run through downtown Middletown, and then crosses the river. Shortly after entering Dayton, it becomes concurrent with the U.S. Route 35 freeway and then Interstate 75. Route 4 then splits off as a freeway paralleling the Mad River. It then joins Interstate 70, with which it runs concurrently for over three miles. The route splits as a freeway again, until it becomes a one-way pair of surface streets in downtown Springfield.

North of Springfield, the route is primarily a two-lane rural highway until its end in Sandusky. It travels through downtown Mechanicsburg and Milford Center, but bypasses downtown Marysville. It then travels through the downtowns of Marion and Bucyrus, crossing the St. Lawrence River Divide in the latter. It finally heads northeast to Sandusky, where it ends.

In 1912 the Route ran from Sandusky to Columbus. In 1924 the Route extended south from Columbus on former SH 5, following current US 23 alignment from Portsmouth to Waldo, and current SR 423 from Waldo to Marion. In 1926, alignment from Portsmouth to Marion certified as US 23; SR 4 realigned south of Marion to its current southern terminus in Cincinnati, replacing the former SR 6 from Cincinnati to Middletown, the former SR 52 from Middletown to 3 miles (4.8 km) south of Milford Center, and the former SR 38 from Marysville to Marion.

In 1959 alignment from Dayton to Springfield rerouted and upgraded to freeway; segment through Fairborn around Wright-Patterson Air Force Base designated as SR 444. In 1967 the segment from SR 201 to SR 444 upgraded to freeway. In 2011 the Dayton segment was rerouted via I-75. In 2021 the Dayton segment rerouted from Germantown Pike to Gettysburg Avenue interchange with US 35.^{[better source needed]}

The intersection of SR 4 and New Carlisle Pike/Lower Valley Pike in Huber Heights, between SR 235/Chambersburg Road and Interstate 70, has had at least 15 accidents between 2012 and August 2018, resulting in three fatalities and 20 injuries. The intersection, which is uncontrolled, is along a high-speed portion of SR 4 that is near-expressway in character; additionally, the median is not wide enough to allow longer vehicles such as tractor-trailers to wait there safely before making a left turn (north) from New Carlisle Pike onto SR 4. Fixes for the problem intersection, all rejected, included adding lights and signage; closing the intersection; adding a traffic light; constructing a roundabout; adding an overpass; requiring traffic from New Carlisle Pike to northbound SR 4 to instead travel southbound to the SR 235/Chambersburg Road interchange, exit and re-enter northbound; and rerouting New Carlisle Pike to Chambersburg Road. At the August 6, 2018 Huber Heights city council meeting, an engineering firm hired by the city, working in conjunction with the Ohio Department of Transportation (ODOT), proposed two alternatives. The first, a restricted crossing U-turn (RCUT) (also known as a superstreet), would prohibit left turns from New Carlisle Pike or Lower Valley Pike, and cross-traffic between the two; those movements would be accomplished via right turns onto SR 4, followed by designated median U-turns. Left turns from SR 4 to New Carlisle Pike and Lower Valley Pike would still be permitted. This alternative has an estimated cost of $1 million, with ODOT paying 80% of the cost and the city paying 20%. The second alternative, sometimes called a "basic RCUT", is similar to the first alternative, but would additionally prohibit left turns from SR 4 to New Carlisle Pike and Lower Valley Pike; those movements would be accomplished via median U-turns, followed by right turns. This alternative's estimated cost is $701,000, using the same 80%/20% cost split. A superstreet already exists along the SR 4 Bypass in nearby Butler County.