The obstructed space available for lateral daily traffic volume. Median Crossovers a Neighbourhood objection to nightime noise. White segments may be reflectorised. Log In Sign Up.
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Geometric design elements such as alignment, gradients, sight distance and crosssection are directly affected by topography, and must be selected so that the road designed will reasonably fit into those natural and manmade features and economise on construction and maintenance. The natural ground, cross slopes i.
ROLLING terrain means: The topographical condition where the natural slopes consistently rise above and fall below the road or street grade and where occasional steep slopes offer some restrictions to normal horizontal and vertical roadway alignment.
MOUNTAINOUS terrain means: The topographical condition where longitudinal and transverse changes in the elevation of the ground with respect to the road or street are abrupt and where benching and side hill excavation are frequently required to obtain acceptable horizontal and vertical alignment. Steep grades and restrictive passing sight distance greatly reduce the capacity of a 2lane road and lower the running speed of traffic, whereas their effect on wider roads is much less.
Consequently, the nature of the terrain sometimes determines the type of road to be built. Topographic conditions may also affect the cross-sectional arrangement of divided roads. In urban areas, land development for residential, commercial and industrial purposes will restrict choice of road location, lower running speed,generate more turning movements, and require more frequent; intersections than in open rural areas.
Geologic and climatic conditions must also be considered for the location and geometric design of a road. Since topography and land use have pronounced effect on road geometrics, information regarding these features should be obtained in the early stages of planning and design.
Aerial surveys gener ally expedite the collection of these data. Topographic maps of suitable scale form the necessary base for preliminary location. In the preparation of final plans a scale of is generally used, and sometimes a scale of on sup plemental drawings to show particular details. The topographic maps should be supplemented by further data regarding subsurface and drainage conditions, the value of land, size, type and value of buildings, planning for the improvement of the area, and other information that may affect or be affected by the road.
Traffic data for a road or section of road generally are available from the most recent edition of "Traffic Volume Peninsular Malaysia" published by the Highway Planning Unit of the Ministry Of Works. Knowledge of the ADT is important for many purposes, such as determining annual usage as justification for proposed expenditures or for design of structural elements of a road.
The projected ADT is also used to designate the standard of road as shown in Table A more appropriate measurement is by hourly volume which is used to deter mine the capacity requirement of the road. It is difficult to determine which of these hourly traffic volumes should be used for design. It would be wasteful to base the design on the maximum peak hour traffic of the year, yet the use of the average hourly traffic would result in an inadequate design.
To determine the hourly traffic best fitted for design, a curve showing the variation in hourly traffic volumes-during the year is used. The Highway Planning Unit of the Ministry of Works should be consulted for the survey data if available.
In the absence of the traffic survey data, the hourly traffic used in design is the 30th highest hourly volume of the. The above criteria is applicable to most rural and urban roads. However, for roads on which there is unusual or highly seasonal fluctuation in traffic flow such as holiday reasort roads, the 30HV may not be applicable.
The Highway Planning Unit of the Ministry of Works should be consulted for the traffic data if available. For roads with highly distinct fluctuations of traffic, whether seasonal, dayly or hourly, it is recommended that traffic surveys be carried out as the above k val ues may be unrealistic. For 2-lane roads, the DHV is the total traffic in both directions of travel.
On roads with more than two lanes, and on 2-lane roads where important intersections are encountered or where additional lanes are to be provided latter, knowl edge of the hourly traffic load in each direction of travel is essential for design.
Generally in the absence of field data D value of can be used in urban areas and in rural areas. Traffic distribution by directions is generally consistent from year to year and from day to day except on some roads serving holiday resort area. Vehicles of different sizes and weights have different operating characteristics, which must be considered in geometric design.
Commercial vehicles generally are heavier, slower and occupy more roadway space and consequently impose a greater traffic effect on the road than the passenger vehicles. The various sizes and weights of vehicles as they affect traffic operation can be grouped into six 6 categories conforming to the classification for the National Traffic census:i. Desirably, a road should be designed to accomodate the traffic; that might occur within the life of the facility under reasonable maintenance.
This is seldom economically feasible and is difficult to estimate. The projection of traffic for use in the design should be based on a period of 20 years after completion of the road. In areas where traffic estimation is difficult due to uncertainty in land use, planning or roadside interference, the design of the formation width shall be based on a period of 20 years, but pavement construction maybe staged basing on a 10 year period for the first stage.
The Highway Planning Unit should be consulted for the projection of traffic over the design period. Page
Arahan Teknik (Jalan) 8-86 - A Guide on Geometric Design of Roads
Arahan Teknik-Cawangan Jalan