SCDOT's OSOW office has the discretion to allow permits for extra-large cargo trailers and rigs based on a number of factors: road size, weight capacity, bridge and overpass heights and capacities, and community safety issues. Commercial and private haulers must obtain a password to the permitting interface on the OSOW website by calling SCDOT; once the login information is received, you can apply for an OSOW permit online. In most cases, your application will be granted, but the OSOW office maintains the right to specify the route along which you are allowed to haul your trailer. The website login page also lists construction advisories and other considerations.
Many standard-sized cargo trailers are too heavy or wide for certain bridges. Although these trailers do not need an oversize permit for the state, their drivers do need to know where not to go because of bridge restrictions. The SCDOT maintains a page of restricted bridges by county, but urges you to contact individual county administrations if you think there might be an issue because the state does not update this information frequently. As a first step for bridge information, click on the county in the SCDOT site page in Resources to review bridge information. For example, Berkeley County lists four bridges that restrict loads to less than 43 and 33 tons respectively. The counties table indicates what communities the bridges are in and what the route names/numbers are.
The Blue Ridge Parkway, for example, does not permit commercial vehicles, so if your rig or trailer are commercial, you cannot take them on this route; you probably wouldn't want to anyway as the speed limit is only 45mph. If you plan to tow your trailer on any of South Carolina's toll roads, you may want to contact the toll operations center before traveling as there are sometimes size and weight limitations for trailers.
