Justification
Two-lane freeways are usually built as a temporary solution due to lack of funds, as an environmental compromise or as a way to overcome problems constrained from highway reconstruction when there are four lanes or more. If the road is widened, the existing road is typically allocated to traffic going in one direction, and the lanes for the other direction are built as a whole new roadbed adjacent to the existing one. When upgraded in this manner, the road becomes a typical freeway. Many two-lane freeways are built so that when the road is upgraded to a proper divided freeway, the existing overpasses and ramps do not need reconstruction.
A super-2 expressway is a high-speed surface road with at-grade intersections, depending on the common usage of the term expressway in the area. By this definition, Super-2s can be considered the first stage of project which is expected to become a full freeway, with the transportation authority owning the land necessary for the future adjacent carriageway. At-grade intersections exist but there is sufficient land to replace them with interchanges. In some US states, a super-2 expressway is simply referred to as a super-2, regardless of whether it is fully controlled-access or not. Highway 410 in Ontario was originally a super-2 before being upgraded to a full freeway.
A super-4 expressway is a multi-lane divided highway with at-grade intersections, although the highway will become a full controlled-access freeway if the intersections are replaced with interchanges. A super-4 may have formerly been a super-2 that has been twinned, although such instances of super-4 intermediaries are rare as super-2s are often upgraded right away to full freeways. Highway 40 in Ontario is a super-4 expressway between Highway 402 and Wellington St., and from Indian Rd to Courtright. The remaining sections of Highway 40 are super-2 expressways. Other super-4 expressways include the Hanlon Parkway in Guelph and the Black Creek Drive in Toronto, both which have sufficient right of way to allow for interchanges and overpasses to replace the at-grade crossings.
When a super-2 expressway is converted to a 4-lane divided freeway, conversion artifacts such as double yellow lines, or broken yellow lines in passing zones are usually cleanly bestowed in favor of more consistent road marking for 4-lane divided expressways.
Read more about this topic: Two-lane Expressway