2 A road to be designed from A to D located 11000 ft apart T

2. A road to be designed from A to D located 11,000 ft apart. Two alternatives are available for the vertical alignment of the road. Alternative 1 uses one grade from A to D, whereas alternative 2 goes through B and C as shown below. . The elevations of points A, B, C and D are 1,000, 1,270, 1,270 and 1,540 ft, respectively. Which alternative would provide a better operating speed of a typical truck starting at a speed of 50 mph at point A? What can you conclude from the results of this problem as far as designing a steep and long grade between two points? 3,000 ft 5,000 ft 3,000 ft

Solution

Solution:

case 1:

Point A to B the Gradient is 14%, Which is Greater to the Exceptional gradient mountain terrain,and steep terrain having elevation upto 3000m of value 8%.

In this cases the length of road is very critical length of road.

So here Gradient lies between A&B IS RANGE 12 To 15%,So reduction in vechicle speed as compare to flat grade %.

In Light vechicle 10-15 km/h, In heavy vechicle 15% maximum negotible .

This type of Road is suitability for low volume load (very few or no commercial vechicle)

Case 2 :

The gradient between A and B is 33% Which is greater to exceptional gradient.

In case of light vechicle very low, In case heavy vechicle not negotiable.

In cases of C to D the gradient value is 51% , so such high gradient in not use for any type of traffic.

Note: Case 1 type road is given better operating speed as compare to Case 2:

To better design in case 2 , in portion A to C provide summit curve and portion B to D provide valley curve , If doing this the case 2 is more suitable for operating speed,