Parley’s Summit

Parley's Summit is the high point of Parleys Canyon, the corridor I-80 uses to climb out of the Salt Lake Valley. Eastbound you grind up out of the city toward the Snyderville Basin and Park City, then on toward Wyoming. Westbound it flips: a long, steady descent straight into a major metro. AARoads puts the I-80 roadway summit at 7,016 feet, at Exit 140. That is the number a trucker actually drives over. (Wikipedia's article body lists the geographic pass higher, at 7,120 feet, and calls it the highest point on I-80 in Utah. A nearby NRCS snow-telemetry station reads 7,590 feet, but that gauge sits on higher ground off the roadbed, so do not treat it as the road elevation.)

What makes this grade matter is the drop. I-80 falls more than 2,400 feet between the summit and Salt Lake City, on a 3 to 6 percent grade, and trucks are held to 40 mph (AARoads). That is a sustained descent into stop-and-go city traffic, which is exactly the setup that overheats brakes. The canyon also has a runaway truck ramp on the westbound left side near milepost 135, roughly 3.5 miles below the top (AARoads), and it has been used.

Parley's stays open year-round. There is no scheduled seasonal closure here. When snow stacks up, UDOT enforces its Traction Law through the canyon, and in the worst conditions it can require chains or 4WD for every vehicle, not just semis. Full closures happen, but they are event-driven: crashes, slide-offs, severe weather, and on one occasion a wildfire that shut both directions. Plan around the descent and the winter traction rules, and check signs and the UDOT Traffic app before you commit to the grade.

• I-80 roadway summit is 7,016 feet at Exit 140; this is the trucker-relevant figure (AARoads)
• Wikipedia's article body lists the geographic pass at 7,120 feet and calls it the highest point on I-80 in Utah (Wikipedia)
• The grade runs 3 to 6 percent and trucks are limited to 40 mph (AARoads)
• Westbound I-80 drops more than 2,400 feet between the summit and Salt Lake City (AARoads)
• Runaway truck ramp sits on the westbound left side near milepost 135, about 3.5 miles below the summit (AARoads)
• Utah's Traction Law (rule R920-6) Class 1 applies to vehicles over 12,000 lb GVW, including semis (UDOT Wasatch Back)
• No scheduled seasonal closure; it is a year-round interstate, with closures driven by crashes, weather, or fire

There is no fixed chain-control season on Parley's. UDOT does not publish hard start or end dates for the canyon. The Traction Law applies when road surface conditions warrant, so the rule turns on with the weather and turns off when the road clears, not on a calendar. When it is active, Class 1 covers vehicles over 12,000 lb GVW (buses, semis, some RVs) and Class 2 covers all vehicles; UDOT announces which class is in effect through road signs, message boards, the UDOT Traffic app, and its social media (UDOT Wasatch Back). General guidance says commercial drivers should carry chains roughly October through April, but that window is a guideline, not a verified Parleys-specific UDOT rule. In severe snow UDOT can escalate to chains or 4WD for every vehicle, as it did eastbound at milepost 128 on Nov 28-29, 2019 (Fox 13).

The canyon and summit are named for Parley P. Pratt, who explored and built a toll road through what was then called Big Canyon. Construction started in 1848 and finished in 1850, and the road became the primary way into the Salt Lake Valley, displacing the older Emigration Canyon route (Wikipedia). A railway ran through the canyon from 1881 until 1956 (Wikipedia). The modern highway grew out of U.S. 40, which was widened to four lanes through the canyon in the mid-1950s and later overlaid by I-80 (AARoads). UDOT reconstructed the canyon road in the 2010s: the Parleys Canyon chain-up area was rebuilt during 2013 work, and a Renovate I-80 project from June 2014 to October 2015 rebuilt the roadway between Silver Creek Junction and Wanship in concrete (AARoads).

The canyon's most dramatic recent event was fire. On Aug. 14, 2021, the Parleys Canyon Fire ignited just after 1:15 p.m. off I-80, closed the interstate in both directions, and forced evacuations across Summit Park, Pinebrook, Lambs Canyon, and upper Mill Creek. An estimated 6,000 to 8,000 homes fell under evacuation orders, and the fire grew past 2,000 acres within hours (Salt Lake Tribune; Deseret News; KSL). Investigators traced the cause to hot particles from a vehicle's failing catalytic converter (Utah DPS).