These are turning roadways. The width varies, depending upon percent trucks, the provision for passing a stalled vehicle and curvature. Curbing type also affects the width some too. Hope this helps!

Exhibit 10-67 covers the various scenarios for ramps. However if you are talking about acceleration/deceleration "lanes", or speed change lanes, page 848 of the 2001 Green Book states that these are "added lane(s) joining the traveled way of the highway with thatof the turning roadway and do not necessarily imply a definite lane of unifirm width. This additional lane is part of the elongated ramp terminal area". See also Exhibit 10-69/10-70...these show the recommended minimum widths at specific lengths along the tapers/parallel lanes.