between a controlled-access highway and a road without access control. The controlled-access highway is called the mainline, and the uncontrolled road is called the crossroad. More complex interchanges involving many roads may have characteristics of both types of interchanges as required. The number of directions one can travel toward or away from the interchange on all of the roads involved is the number of "legs". When two roads meet, there are four paths to and from the interchange, and so the interchange has four legs, but if one of the roads terminates at the interchange, it will only have three legs. Interchanges with more legs require joining elements from four- and three-legged interchanges in order to permit travel from any one direction to any other direction. If all possible connections exist, it is a complete interchange providing complete access; if not, it is an incomplete interchange providing incomplete access. Limited-access road A limited-access road, often called a limited-access highway (US), divided highway (US), or dual carriageway (UK), and in some situations an expressway, is similar to a controlled-access highway in that it conforms to many or most of the standards that controlled-access highways follow, but does allow some uncontrolled access to local roads. They can be viewed as a middle ground between controlled-access highways and arterial roads. The degree of isolation from local traffic varies between countries and regions, as does a precise definition of the term itself. Controlled-access highways can also be viewed as a subset of limited-access highways that has stricter requirements. Arterial road An arterial road or arterial thoroughfare is a road without controlled access that can carry a large volume of local traffic at a generally high speed, being below controlled-access highways in the hierarchy. Because their primary function is to connect collector roads (below) to controlled-access highways, some are considered limited-access roads. Intersections of arterial roads are almost always at-grade, and use traffic signals to coordinate traffic that would otherwise intersect, but traffic signals are often omitted when minor collector roads intersect, usually placing a stop sign at the collector road to prevent the traffic on the arterial road from being impeded. Arterial roads almost always have multiple lanes to allow for high capacity. They do not allow for access to residential properties under most circumstances. Collector road A collector road, also known as a distributor road, is a road that allows high access to