TABLE OF CONTENTS Collector-distributor (C-D) roads are used to minimize weaving problems and reduce the number of conflict points (merging and diverging) on the mainline. C-D roads may be used within a single interchange, through two adjacent interchanges, or continuously through several interchanges.
When a C-D road is provided between interchanges, a minimum of two lanes should be used. Either one or two lanes may be used on C-D roads within a single interchange. The cross-section elements for one- and two-lane C-D roads should be in accordance with the criteria for one-lane and two-lane directional roadways provided in Fig. 2.25. The separation between the mainline and C-D road pavements should be designed to prevent, or at least discourage, indiscriminate crossovers. As a minimum, the separation should be wide enough to provide normal shoulder widths for both the mainline and C-D road roadways plus a suitable median. Normally, a standard concrete barrier median is used, since C-D road separation often involves obstructions such as bridge parapets, piers, or overhead sign supports. There may be isolated cases where a lesser-type median may be used.
Figure 2.45A shows both class I and class II C-D road entrance terminals. The class I collector-distributor entrance terminal is intended for use on rural interstate highways and other freeways where class I design has been designated. The class II collector-distributor entrance terminal is intended for use on all other freeways. Three exit terminal lane conditions...
