Designing a Divided Rural Multilane Highway and Transition Curve Parameters

Designing a Divided Rural Multilane Highway

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A divided rural multilane highway is required to cope with an AADT of 35 000 veh/day. A 60 mi/h design speed is chosen with lanes of a standard 3.65 m width and obstructions within 0.61 m on both sides of roadway. The terrain is rolling and the percentages for the various heavy vehicle types are as follows: PT = 6%, PB = 4% and PR = 7%. The Driver Population is “Ideal”. The Peak Hour Factor (PHF) is 0.85 and the Directional Factor D is estimated at 0.65.

If the highway is required to maintain LOS C and it is to be designed to cope with the 30th highest hourly volume during the year, calculate the followings:

The number of lanes in each direction.

If the client requires a reduction of 1 lane per direction, demonstrate what is the best solution to adopt amongst the followings:

1. a) extending the “Distance to obstruction from travelled edge” up to 1.83 m;
2. b) rearranging the whole highway over a type of terrain from “rolling” to “level”.
3. c) designing to cope with the highest hourly volume during the year.

Critically discuss and prove by calculation-based evidence any potential solution(s) other than those at point 1.2, that may reduce the number of lanes for the concerning highway (hint: keep constant the following parameters: divided multi-lane arrangement; AADT = 35000 veh/day; Design Speed = 60 mi/h; lane width = 3.65 m; “ideal” driver population; PHF = 0.85; D = 0.65).

A transition curve is required for a single carriageway road with a design  speed vdesign = 23.61 m/s. The bearings of the two concerning straights are 20° and 59°. Assuming a value of 0.45 m/s3 for C and a superelevation e = 7.0%, calculate the followings (clearly reference the concerning ruling equations and provide step-by-step calculations and drawings, where required):

The transition length, L.

The length along the tangent required from the intersection point to the start of the transition, IT? .

The form of the cubic parabola and the coordinates of the point at which the transition becomes the circular arc of radius R.

Plot the transition curve assuming a proper offset for the largest x or y coordinate.

The optimum value of “rate of change of radial acceleration” Copt that meets the criterion L ≤ Lmax with the least difference (L = length of the transition curve; Lmax = maximum length of transition curve recommended by the UK Standards)? (round up Copt to the 2nd decimal digit).