SU0002276 - Laserfiche WebLink

Home Browse Search

900-4 HIGHWAY DESIGN MANUAL July 1, 1990 themselves to top trimming will not be forbs, wildflowers, inert material. or any permitted under utility wires. combination of the above; or Large trees may be planted in the median of (b) All feasible alternatives to correct the defi- conventional highways when all of the following ciencies would consume as much or more requirements are met: water than the permanently irrigated (a) There is an existing speed zone of 35 tulles ground cover. per hour or less. A temporary cover crop of ground cover is (b) The median is curbed and the curbs are at an acceptable method of controlling erosion least 12 feet apart. while trees and shrubs are maturing. (c) The trees are kept at least 6 feet from the Species which have proven to be durable curb and at least 50 feet from the end of under highway conditions should be used. A any median strip or a greater distance if small percentage of untested but promising necessary to preserve sight distance. plant material is permissible to expand the plant palette. (d) The trees will not lower sight distance be- Plants that are known to have significant low required standards (see Topic 201). pest or disease problems should not be used. (e) The trees must be located so that the mo- Invasive or noxious species and plants which torist's clear vision of any highway signs or host serious pests should not be used where signals will be assured at all times. they will endanger adjacent agricultural areas or natural plant communities. 902.4 Planting Guidelines Plants with edible or attractive fruits or nuts (1) Plant Selection. Plants should be toler- should not be planted along roadways. ant of local environmental conditions such as Seedlings or plants in small containers temperature, soil, water quality, air quality, and should be used unless special circumstances wind. Available rainfall should be considered so justify specimen material. Direct seeding, bare that irrigation can be held to a minimum. All root, and balled and burlapped methods should other factors being equal, locally native plants be considered. should be the first choice. (2) Plant Placement Plants should be Preferably, planting should not require per- placed so that pruning will not be required. manent irrigation. This may not be possible in Conflicts with paving, underground facilities, arid regions and in certain situations. When and structures should also be avoided. permanent irrigation is necessary, plants should be selected which would have the great- Plants with similar water requirements should be grouped for irrigation purposes. est chance of survival if water were to become unavailable. Plants that may attract wildlife should not Plants should have the proper growth rate, be placed near the roadway, longevity, size, and appearance for their in- Trees with brittle branches should not be tended uses. Wherever feasible, trees should be placed where falling material will create a haz- used to create the main structure of the plant- and or require excessive maintenance. Ing composition. Ground covers should not be used in situa- 902.5 Irrigation Guidelines tions where permanent irrigation will be nec- essary, unless: Irrigation systems should be simple and straightforward. Standard, commercially avail- (a) Basic functional safety, environmental, or able components should be used and special aesthetic deficiencies cannot be corrected features should not be specified unless they are with trees, shrubs, drought tolerant ground needed. Standard state-furnished controllers covers (i.e.. those which require no irriga- must be used as directed by the Office of Land- tion or temporary irrigation only), grasses, scape Architecture.