using cementing admixtures as required. To the extent possible measures should be taken to insure a uniform moisture content of the subgrade.
CROSS SECTIONS
Typical cross sections are shown in plate 28. As indicated, all traffic lanes of the proposed roads would be 12 feet wide. On two-lane roads these lanes are shown as separated by a traversable dividing strip 2 feet wide. This is believed to be a desirable feature; in fact a more positive division between the lanes of opposing traffic would be desirable, but on two-lane roads is impossible because of the necessity of using the opposing traffic lane as a passing lane. For this reason the narrow dividing strip provided should be built as a traversable surface, flush with the surface of the traffic lanes, but contrasting with them in color and texture, so that drivers will be warned both visually and physically when they cross it or encroach upon it.[1]
Where the expected traffic volume justifies the construction of more than two traffic lanes, four lanes built in pairs, the pairs separated by a parkway strip at least 20 feet wide in suburban areas and 40 feet wide in rural areas, would be provided. These widths of medial parkway strips are ample and may, in exceptional cases, be reduced, since the separation of grades at intersections obviates need of the parkway for protection of crossing vehicles. Sections of the selected routes on which two- and four-lane pavements would be required are shown on plate 29.
Each two-lane pavement would be designed to drain to both sides and drainage would be provided in the medial parkway strip. This design is particularly advantageous in sections subject to snow. The parkway is a convenient area on which to store the snow which, when melted, runs off into the central drain instead of flowing across the pavements to create a serious hazard in case of sudden freezing.
Shoulders would be invariably 10 feet wide to provide adequate space for stopping off the pavement. In construction they would be sufficiently strong to support the weight of vehicles in all weather.
Slopes of cuts and fills would be designed to prevent erosion. Where feasible, fills would be made to a slope of 1 on 4 or flatter to avoid the use of guardrails and in no case, except perhaps in some mountain locations, would their slope be steeper than 1 on 2. Cut slopes would be varied according to the character of the materials encountered and the depth of cut. All cut slopes would be liberally rounded for both stability and appearance; and no hazardous breaks, such as deep ditches, would be permitted. At ends of cuts and fills, slopes would be made progressively flatter so that they would gradually merge with the ground and with each other.
Low curbs, with flat slopes readily mounted in emergencies, would be used in park areas and on the inside of curves where necessary to control drainage and reduce the maintenance of shoulders or medial parkway strips. Curbs of this character would be contiguous with the pavement proper. Curbs intended to prevent vehicles from leaving the pavement, as at walls and bridges, would be of the barrier type, set at least 2 feet from the edge of pavement. All curbs should be highly visible day and night.
- ↑ The cost of such dividing strips is not included in the subsequently tabulated estimates.
