Geometry > Circulating Geometry > Circulating Lanes nc

Circulating Lanes nc

This section must be read in conjunction with the one above on circulating width C.

HCM uses the number circulating lanes nc.

nc+ should not be less than e except when ne has exclusive right turn lanes so that the remaining ne is not greater than nc+.

C / nc = the circulating lane width.

Single lane widths should typically be between about 16 ft and 20 ft. Multiple lanes should be between about 14 ft and 16 ft.

If the central island has a truck apron then the lane next to the central island can be narrower (13 or 14 ft) with other lane(s) wider than the inner lane. This helps reduce entry path overlap and give wider lanes for trucks making a through movement or especially a right turn. With a truck apron and three circulating lanes the lanes can have three different widths with the narrowest next to the central island and widest the outer lane. The narrow lane and truck apron accommodate trucks. The middle lane does not need to be very wide for truck through movements, and the wide outer lane generously accommodates both through truck movements and more importantly right turns, which are often the most difficult truck movement.

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