FLH PDDM Chapter 9 - Eastern Federal Lands Highway Division

9.4.B. Intersection Design. (continued)Try to limit the use of curbing to urban and suburban highways with a design speed of 60 km/h or less. Onthese types of highways, drivers expect to encounter confined facilities and raised channelization works well.The two general classifications of curbing for channelization are mountable curbs and barrier curbs of the typesshown in Figure IV-4 on page 346 of the Green Book. For safety considerations, use mountable curbingwhenever possible. Use barrier curb for raised islands with luminaries or traffic control devices and forpedestrian refuge.Table 9-12 shows the minimum offset distances recommended for barrier curb. For mountable curbinginstallations, the left offset distance is optional.Table 9-12Offset Distances for Barrier CurbLane Left RightWidth Rural Urban Rural and Urban(m) (m) (m) (m)3.6 0.3 0.3 1 minimum3.3 0.6 0.3 1 minimum3.0 1.0 0.6 1 minimum6. Traffic Islands. A traffic island is a defined area between traffic lanes for control of vehicle movements,pedestrian refuge or traffic control devices. The use of raised traffic islands should be limited to those urbanand suburban highways with a design speed of 60 km/h or less.Traffic islands perform these major functions:Channelization islands control and direct traffic movement.Divisional islands separate opposing or same direction traffic streams.Refuge islands provide safe haven for pedestrians.Miscellaneous islands provide for proper placement of traffic control devices.Divisional and refuge islands are normally elongated and should be at least 1.2 meters wide and 6 meters long.Channelization islands are normally triangular. In rural areas they should contain an area of at least 7 squaremeters with 9 square meters as a desirable minimum. In urban areas where speeds are low, islands abouttwo-thirds this size may be acceptable. Islands with traffic control devices or luminaries and islands crossedby pedestrians require 18 square meters as a minimum area.Design triangular shaped islands as shown in Exhibit 9.7. The offset distances illustrated apply to islandsconstructed with mountable curbs. For painted islands in rural areas, these offset distances are desirable butnot mandatory. With barrier curbing provide the minimum offset distances shown in Table 9-12 but not lessthan those shown in Exhibit 9.7. Increase the offsets of the approach noses of the islands when the minimumoffset distance shown in Exhibit 9.7 is increased.9 - 62