In 1955, the northern terminus was moved from US 6 in Clarks Summit to its current location.

In 1989, the route was changed to follow Moosic Street, Jefferson Avenue, Mulberry Street and the North Scranton Expressway in Scranton.

A sinkhole, which had caused issues in 2007, reopened on February 5, 2014 on the southbound side of the Scranton Expressway between the Mifflin Avenue intersection and Seventh Avenue/Providence Road interchange.  The hole opened up as soon as a  PennDOT snowplow had passed over the area while clearing the travel lanes after a snowfall, which prompted the agency to initially close the southbound passing lane and then later both passing lanes.  The lanes were reopened after three days of repairs that included filling the hole with a concrete mix.

In 1932, the route was paved between Clintonville to Kennerdale Road.  In 1936, the southern terminus was moved from Clintonville to its current location.

In 1941, the southern terminus was moved to PA 356 northeast of Saxonburg via Saxonburg Road, Water Street, and Nuepert Road from its current location.  In 1946, the southern terminus was moved from PA 356 back to its current location.

In 1976, the northern terminus was moved to the Richard C. Frame Memorial Highway.

In 1970, work to divide the route between Coopersburg and Center Valley got underway, with its completion a year later.  A median was installed in 1973 from Tamaqua to the Rush Township line.  In 1976, construction began on the section of Crossvalley Expressway from Luzerne to Rutter Avenue.  In 1978, the bridge over the Susquehanna River opened.  That year the designation was moved to Park Avenue, South Street, River Street, and Market Street to end at US 11.  Also a median was installed from the Schuylkill Township line to Hometown in 1978.

Construction on the section between River Street and Main Street began in 1981, while the section from Luzerne to Rutter Avenue opened to traffic in 1982.   A median was installed in 1983 from DeKalb Pike to Montgomeryville.  In 1984, the southern terminus was moved to its current location.  Prior to that, it traveled down Ogontz Avenue to Stenton Avenue and end at PA 611 there.

Construction began on the section of the North Crossvalley Expressway from Kidder Street to Wilkes-Barre Boulevard in 1989.  This section opened in 1992 and included an upgrade of Kidder Street to I-81 to expressway standards.  Also, that is when PA 309 was moved onto I-81 from Exit 165 to Exit 170B from Wilkes-Barre Township Boulevard, Spring Street, and Kidder Street.

A $5.6 million improvement project began March 24, 2004 between PA 463 in Montgomery County and Church Road in Bucks County.  Work entailed widening the roadway from four to five lanes to provide a center turn lane, reconstructing shoulders, resurfacing the roadway, installing curbs and pavement markings, improving drainage, and upgrading traffic signals at Richardson Road, Broad Street, and Walnut Street.  Also included in the scope of the work was rehabilitating four bridges along PA 309.  "PennDOT is extremely pleased to begin this safety improvement project on Route 309," PennDOT District Administrator Andrew L. Warren said.  "After the project is completed, Route 309 motorists will find it safer and easier to access business and side streets along this important corridor because of the new center turn lane."  Construction wrapped up in summer 2004.

A wrong-way driver gave commuters a scare on the morning of March 23, 2011.  The ordeal began when the motorist took the Lawn Avenue off-ramp northeast of Sellersville, confusing it for a driveway, and traveled southbound in the northbound lanes for five miles.  Officer Jerry Fish of the Hilltown Township Police Department managed to catch up to the motorist and get her to stop, fortunately before anyone was hurt.  The driver was held overnight at a local hospital for evaluation.

Work began on a safety improvement project in April 2014 between Wilkes-Barre and Mountain Top in Luzerne County.  The $5.2 million project widened the rock cut which PA 309 traverses to reduce water runoff and allow more sunlight to hit the road surface to reduce the formation of ice during the winter.  Initially construction was to wrap up on January 6, 2015, but due to snow and ice on the highway, it reopened two days later.

An early season snow storm hit the eastern part of Pennsylvania on November 15, 2018 and wreaked havoc with travelers of all species.  Motorists noticed a camel next to a vehicle that was pulled over in the northbound lanes near the PA 113 interchange in Bucks County.  The driver had let it out of the trailer because owner would not have wanted the camel inside the trailer while stopped in the event it was rear-ended.

The Jewish Federation of Greater Philadelphia gave the name of and reason for the camel's appearance:

Sadly, Einstein was unable to make the show after the driver decided that due to the weather it was best to return to the Peaceable Kingdom Petting Zoo, a mobile petting zoo based in Quakertown.  However, Einstein's fame grew as Twitter hailed him a hero, someone in Easton makes and sells t-shirts of the "snow camel," and Molly's Irish Grille & Sports Pub in Bethlehem created a drink named the Snow Camel.  It is comprised of coffee, Wild Turkey and Dorda Double Chocolate Liqueur, and topped with whipped cream and Hershey's syrup.

In 1941, the designation was moved from Graffius Avenue and placed on its current alignment north of Punxsutawney.

Until 1986, the northern terminus was in Allens Mills.  It was replaced with PA 830 from US 322, and the northern terminus was moved to its current location.

In 1946, the eastern terminus was moved from PA 113 and PA 413 in Kulps Corner to US 202 east of Doylestown, when the section from US 611 to US 202 completed.  In 1977, the eastern terminus was moved to PA 263 when that part completed.

Signed in 1964 in its current location.

A median was installed in 1958 from the current location of Interstate 81 to US 11 in Moosic.

In 1965, the Department of Highways began upgrading PA 315 from Wilkes-Barre/Scranton International Airport to Moosic.  The following year that section opened at PA 315's northern terminus was moved to Interstate 81 at Exit 178.  A median was installed in 1967 at the Pennsylvania Turnpike Northeast Extension's Exit 115.

In 1978, the southern terminus was moved to US 11 in Plymouth.

Until 1985, the southern terminus was at US 11 in Plymouth.  It wound its way through Wilkes-Barre via West End Road, Carey Avenue, Horton Street, Main Street, Blackman Street, Wilkes-Barre Township Boulevard, Spring Street, and Kidder Street from its current terminus.

In 1986, the northern terminus was moved from I-81 at Exit 178 to end at US 11 in Dupont via Main Street.  In 2001, the route was moved back to the former routing, and with that the end of the route became Wilkes-Barre/Scranton International Airport.

In 1941, the designation changed from the PA 917 alignment to its current route between Maryland and Waynesboro.

In 1947, the route's northern terminus was moved from PA 944 south of Upper Strasburg to its current location.  The highway from Chambersburg to Upper Strasburg was demolished and the land turned over to the federal government for the Letterkenny Army Depot.

In 1928, the route was under construction from Peanut to Struthers Road and completed the following year.  In 1930, it was paved from the Ohio state line to Bessemer.

Prepared to replace the viaduct in West Middlesex, PennDOT had to do more than just some geotechnical drilling.  At an open house on the project in 2012, an elderly man came forward to say his father, a contractor, found five cases of dynamite and nitroglycerine blasting caps while demolishing a building in the 1930s to make way for the viaduct which was built in 1941.  The man told PennDOT officials that his father did not know what to do with the dynamite, so he buried the explosives in the ravine below the viaduct.  Crews did not find anything while excavating on July 26, 2012.

Shortly before 10:51 AM on December 7, 2023, the raised bed of a roll-off truck struck the western side of the bridge carrying the route over Interstate 376.  The bridge was immediately closed as the bed ripped through two support beams and damaged a third, then penetrated a couple of feet through the road surface, leaving only two of the five support beams unaffected.  The bed eventually separated from the truck, and the driver was severely injured and was taken to Saint Elizabeth Hospital in Youngstown, Ohio.  PennDOT inspection crews determined that rather than repairing the span, it would have to be rebuilt and demolition took place the following day.  Construction of a $6.5 million replacement span could begin as early as April 2024.  "We are moving at light speed as far as PennDOT is concerned,"’ said PennDOT project engineer Mark Nicholson.  Unlike the previous span, the overpass will be two and one-half feet higher and be comprised of steel rather than concrete.  "Using steel rather than concrete will make it easier to raise the bridge," said Richard Schoeder, an engineer with Michael Baker International.  While no bonuses will be given for early completion, daily penalties in the range of thousands of dollars will be assessed against the contract for each day it is late in opening.  PennDOT is seeking to recoup costs of the replacement from the trucking company.

Until 1965, the northern terminus was in Kinzua, which is now under the Allegheny Reservoir near Kinzua Heights.  That year it was truncated to US 6 in Kane and then moved again in 1973 to its current location.

In 1936, the designation was moved off of the current PA 741 between PA 324 and US 222/PA 272 and placed on its current alignment.

Signed in its current location in 1949.

In 1936, the route ended at PA 26 after turning at Chaneysville, but in that year was changed to end at the Maryland state line.  In 1955, the section between Chaneysville and Rainsburg was improved.

In 1963, the route was changed to its current alignment between Charlesville to US 30.  In 1989, the section between Chaneysville and Rainsburg was finally paved.

Signed in 1936 in its final location.

Signed in 1961 on the current alignment.

Prior to 1946, it was signed on the current PA 145 alignment from Tilghman Street in Allentown to Cementon.  Signed in 1946 on its current alignment.

In 2006, the route was moved off the former alignment between SR 4065 and PA 231 in Acheson.

Construction began in 1975 on the Newtown Bypass which opened two years later in 1977.

In 1929, the route was moved from Pleasant Hall to Roxbury via Upper Strasburg to go straight north from Pleasant Hall when that section opened to PA 433.

In 1932, the route was paved from Roxbury to the Cumberland County line.  In 1936, the route's eastern terminus was moved from Shippensburg at US 11 to Roxbury.

In 1947, the route was moved onto the current PA 997 alignment from Letterenny Road and the terminus moved out of Chambersburg due to the Letterkenny Army Depot.

Before 1964, the route designated what is the current PA 997 alignment between PA 433 and Lurgan.  Signed on its current alignment in 1965.  In 1982, the eastern terminus was moved from the US 22/US 322 interchange in Thompsontown to its current location.

In 1947, the route was improved from Izenbrown Corners to Bimber Corners and from Pleasant Road to Lenhart Road.  In 1949, the section from Bimbers Corners to Hearts Content Road was improved.

In 1967, the section between the Sandstone Springs campground and to a point five miles north was paved.  In 1969, the section between Tidioute to the Sandstone Springs campground was paved.

In 1967, the western terminus was moved from PA 8 in Harrisville to its current location.

In 1964, the southern terminus was moved from Bloomsburg to its current location.  In 1966, the northern terminus was moved from PA 254 in Benton to its current location.

In 1955, the western terminus was moved from Harrisburg at Herr Street to Hershey.

In 1961, the western terminus was moved from US 422 in Hershey to PA 441 in Marietta.  In 1967, the western terminus was moved to US 30 at Prospect Road west of Mountville.

In 1970, the route's western terminus was moved to its current location.

In 1932, the route was paved from Fredericksburg to Lancaster Street and Lickdale to Bordensville.  In 1936, the northern terminus was moved from the Borough of Bordensville to US 22 in Harper Tavern.

In 1963, the northern terminus was moved from US 22 in Harper Tavern to Lickdale.  The northern terminus moved to its current location in 1970 from Lickdale.

Signed in 1972 on its current alignment.  The route was extended north of PA 724 to US 422 in December 2008, replacing PA 82 from Birdsboro to US 422.  The reason was PennDOT's decision to forgo replacing three bridges on PA 82 south of Birdsboro that were damaged in a flood caused by a tropical depression on September 8, 1987.

In 1965, the western terminus was moved from PA 59 in Kinzua, which is now under the Allegheny Reservoir near Kinzua Heights, to the New York state line when NYSDOT built a new alignment to NY 280.  In 1977, the route was moved onto the new US 219 expressway from its route on East Main Street between Bradford and Foster Brook.

In 1961, the northern terminus was moved from PA 407 in Carpenter Town to its current location.

In 1975, the southern terminus was moved to its current location from US 22 in Water Street via Tyrone.  A median was installed in 1989 from US 220 to Business US 220.