Interstate 84 (west) starts in the Portland metropolitan area, I-84 is sometimes referred to as the Banfield Freeway or simply "the Banfield", although the official name is the Banfield Expressway. The freeway is named after Thomas H. Banfield, chairman of the Oregon Transportation Commission from 1943-1950.
East of Pendleton, Oregon, I-84 traverses the infamous Cabbage Hill grade (a 6% grade). This grade is legendary for the fact that the westbound lanes switchback twice on its descent into Pendleton. Eastbound lanes feature what are the tightest curves on the Interstate system, even though those curves are on the uphill (eastbound) direction. This grade is also well known due to the fact that it features such a great distance between eastbound and westbound lanes, nearly 2 miles between directions of travel at points.
I-84 enters Idaho at a crossing of the Snake River just east of Ontario, Oregon. From there, it continues on to the major cities of the Boise metropolitan area, including Caldwell, Nampa, Meridian, and Boise (where I-184 connects travelers to downtown). From Boise, I-84 continues on towards Twin Falls after passing near several small towns (such as Mountain Home, Glenns Ferry, and Jerome).
Just east of Jerome I-84 passes within 5 miles (8 kilometers) of Twin Falls, but does not cross the Snake River Canyon or into Twin Falls County. Access to Twin Falls is afforded by an intersection with US 93.
After Twin Falls, I-84 continues through Burley and Heyburn. At the intersection with I-86, approximately 7 miles (11.3 kilometers) east of Declo in rural Cassia County, I-84 veers southeast and heads toward Utah.
From Idaho, I-84 enters Utah at a point approximately 7 miles (11.3 kilometers) from Snowville in Box Elder County. It proceeds southeast towards Tremonton where I-84 joins the route of I-15.
Just south, at Corinne, Utah, I-84 joins the route of the First Transcontinental Railroad which the highway follows to the its terminus. I-15/I-84 pass to the west of Ogden where I-84 separates from I-15 and follows the Weber River. As the freeway passes through Weber Canyon it also passes through several small farming communities, including Morgan, where the Browning Arms Company headquarters can be seen from the freeway. Also visible in the canyon is Devil's Slide, an unusual rock formation just off the freeway.  Farther up the canyon is the 1000 mile tree, planted by Union Pacific Railroad workers to mark 1000 miles from the railroad's origin in Omaha, Nebraska. The freeway ends at Echo, a near ghost town that before served as a stopover for the railroad, at a junction with Interstate 80. Also near the junction is Echo Reservoir and Echo Dam.
Interstate 84 (east) starts in Pennsylvania at Interstate 81 in Dunmore, Pennsylvania, a suburb east of Scranton. I-84 starts as a concurrency with I-380. After several miles, I-84 turns east, towards the New York border through Wayne County and Pike County. I-84 leaves Pennsylvania near Matamoras, Pennsylvania and Port Jervis, New York.
Interstate 84 crosses the New York-Pennsylvania state line near the point where New York, Pennsylvania, and New Jersey meet, lying a mere 30 feet away from New Jersey upon crossing the Delaware River. Signs for the first interchange in New York, in fact, direct motorists to NJ 23. The junction connects to Orange County Highway 15 eastbound, and US 6 westbound. Local lore notes that 84 was originally to cross the tip of New Jersey, near High Point, but the state did not want to maintain so small a piece of highway so far away from the rest of its major highway network.
The New York section of the highway is missing Exit 9 and Exit 14. Exit 9 was supposed to be a clover-leaf intersection with an arterial highway (Alternate 9W) which was on the drawing boards from the late 1950s until well into the 1970s, and appeared as "proposed" on most commercial and government maps produced during that period. The highway was designed to detour traffic away from the downtown City of Newburgh. Eventually, protests by homeowner groups representing neighborhoods which would have been destroyed by the arterial highway, together with soaring property values, forced the state to abandon the proposed highway and instead concentrate its funding on widening Water Street along the riverfront as an arterial (first designated as "Marine Drive" and subsequently as "Rev. Dr. Martin Luther King, Jr., Boulevard"). Tax maps showed a cloverleaf shaped parcel of property just west of the Gidney Avenue overpass in the Town of Newburgh as owned by the State of New York until the late 1980s. The property was sold and is now the site of a medical office complex. To this day, there is no exit between Exit 8 and Exit 10, both in the Town of Newburgh.
Exit 14 was to be the north end of an expressway in the sequence. A new junction, exit 5A, opened November 20, 2007 with a direct freeway link to Stewart International Airport in the Town of Newburgh. Legislation is currently underway to have New York interstate junctions renumbered according to a mile-based system.
In western Connecticut, I-84 is known as the Yankee Expressway from the New York state line to the Bulkeley Bridge in Hartford. Connecticut's Exit 1 offslip eastbound actually leaves the freeway while still in New York at mile 71.2. The state line is at New York state mile 71.46. All lighting and signage relating to the junction is maintained and owned by the State of Connecticut.
Connecticut has the longest designated stretch of I-84 of the four states the highway runs through. I-84 enters Connecticut in the city of Danbury. Within the city, it has a 3-mile concurrency with US 6, US 7, and US 202. US 7 and 202 turn north as a separate expressway at Exit 7, while US 6 heads east at Exit 8, parallel to I-84.
I-84 then heads through Waterbury where it has a junction with the Route 8 expressway. Interstate 691 ends at I-84 near Marion (in the town of Southington) at Exit 27. At Exit 33, I-84 intersects Connecticut Route 72, near New Britain, and has a concurrency with CT 72 for one exit. At Exit 38, I-84 has another concurrency with US 6 in Farmington. The section of I-84 between Waterbury and East Hartford has many left-hand exits and entrances and sharp curves, which were built for a once-planned, but never completed network of freeways around Hartford.
I-84 intersects Interstate 91 in Hartford at Exit 50, after which it then crosses the Connecticut River on the Bulkeley Bridge, overlapped with both US 6 and US 44. Completed in 1908, the Bulkeley Bridge is the oldest bridge on the Interstate Highway System. Interstate 384 begins at Exit 59; the US 6 concurrency ends at Exit 60 as US 6 heads east towards Manchester on a concurrency with US 44. Interstate 291 ends at Exit 61.
Once I-84 leaves Hartford, it is known as the Wilbur Cross Highway. The last exit in Connecticut is Exit 74, an exit for Route 171. I-84 crosses the Massachusetts border near Mashapaug (in the town of Union).
The Wilbur Cross Highway continues on Interstate 84 after the highway crosses the state line. I-84 only has three exits in Massachusetts, before ending at Interstate 90, the Massachusetts Turnpike. I-84 ends at Exit 9 of I-90, which is located in Sturbridge, Massachusetts, 8 miles into the state, which is the shortest distance of the four states I-84 is designated in.