Two separate things can stop you on the Zion-Mt. Carmel Highway over the next two weeks. The tunnel closes from 9 p.m. to 6 a.m. on September 21 through 25 and again September 28 through 30. And if your rig is wider than 7 feet 10 inches, Zion’s own page says you are not permitted on that road at any hour.
The closures are the simpler half. Utah DOT is installing fiber optic cable, and the park published the schedule on September 15, 2026. The closed stretch runs from the east entrance of the tunnel to Canyon Junction. Zion says the dates can move with UDOT’s scheduling, so confirm them before you build a night around them. The park lists Utah 20, Utah 14, and US 89 to Arizona 389 to Utah 59 as alternates, and its own estimate is that they add 10 to 45 minutes depending on where you are headed. If all you wanted was Canyon Overlook Trail, you can still park at the vault toilet nearby and walk about a quarter mile to the trailhead.
The size limits are the bigger story, and most people towing something have not read them.
For a single vehicle with no trailer: 35 feet 9 inches long, 7 feet 10 inches wide, 11 feet 4 inches tall, 50,000 pounds. For a combined vehicle: 50 feet total length, with the trailer no more than 26 feet from hitch to rear axle, and the same width, height and weight caps. Measurements include mirrors, tires, and anything bolted on, which the park spells out as AC units, bike racks and satellite dishes. That is all from Zion’s Large Vehicles page, last updated September 2, 2026.
Width is what catches people, because 7 feet 10 inches is narrower than a lot of rigs before you even fold the mirrors out. The FAQ on the same page puts it without hedging: RVs exceeding the limits will not be permitted past Canyon Junction. Measure yours. Do not assume.
Here is the part we cannot close out. Zion has long escorted oversize vehicles through the tunnel one lane at a time: the park’s May 2024 announcement describes vehicles wider than 7 feet 10 inches or taller than 11 feet 4 inches as requiring a tunnel escort. That same announcement said the park planned to reroute vehicles over these exact dimensions beginning in mid-2026, and the current page reads as a flat prohibition with no permit on offer. But the current page still carries one sentence describing “the current tunnel pass/escort system,” and we could not find an NPS page giving an effective date for the end of escorts. So we are not going to tell you the escort is gone as of a particular day. Call the park at 435-772-3256 before you route anything large through there.
What to do this week: measure the rig, mirrors and all, and write the four numbers down. If you are over on any of them, plan the detour rather than discovering it at the entrance station, where the park says you will be given instructions for turning around. You can still enter through the South Entrance, camp at Watchman or at South Campground when it is open, and drive Zion Canyon Scenic Drive in the shuttle off-season. You just cannot cross the park.
The posted sign and the ranger at the gate beat this page and every other website. If the detour leaves you hunting a night outside the park, free camping in Utah covers what is open on public land nearby, and national park camping rules covers what changes once you are back inside a boundary.