TR 3201 TR 320: Highway Geometric Design Combination of Vertical and Horizontal Alignment

TR 3202 A) Exercise A two lane highway with 3.6 m lanes has a posted speed limit of 80 km/h. On one section has both horizontal and vertical curves with the following details: Horizontal curve: –BC km and EC km with deflection angle of 80 degrees. –Superelevation of 0.08 –A obstruction to sight is 6 m off the carriageway edge of the inside lane –Assumed fs at 80 km/h is 0.14

TR 3203 Exercise … Vertical curve details: –BVC km and EVC km –G1 = +2% and g2 = -4% –PVI is km A recent daytime accident resulted in a fatality and a lawsuit alleging that the posted speed limit of 80 km/h is unsafe an a major cause of the accident. You are required to evaluate and comment on the roadway design

TR 3204 Steps to solution Make a sketch of the situation What is the required sight distance? Assumption of longitudinal friction or consult tables = 160 m Is the horizontal curve radius and superelevation adequate? Is the horizontal sight distance adequate?

TR 3205 Steps to solution 4. Is the vertical curve length adequate? 5. Does the combination of sag and horizontal curves hinder visibility? 6. Comment on the roadway design 7. Give your evaluation of the allegation!

TR 3206 Combination of horizontal and Vertical curves Coordination of distortion points (BVC/SR, EVC/SR to be placed at approximately the same location Curves to be approximately the same length or horizontal curves to lead vertical curves This provides for drainage at flat parts of vertical curves through the superelevated lateral slope

TR 3207 General guidelines - 1 1)Aim at best possible combination of safety, capacity, ease and consistent operation and pleasing appearance (within the practical limits of terrain and land-use). 2)A superimposition of vertical curvature on horizontal curvature results in a more pleasing facility.

TR 3208 General guidelines - 2 3)Sharp horizontal curvature should not be introduced at on or near the top of sharp crest curve 4)Never introduce a sharp horizontal curvature near the bottom of a steep grade or at the low point of a sharp sag curve 5)On two lane highways it is often necessary to work toward long tangents to achieve sufficient PSD

TR 3209 General guidelines - 3 6)The profile and horizontal curvature should be made as flat as practicable at approaches to intersections 7)On Dual highways – use of independent profiles and horizontal alignments for each one way road is sometimes desirable 8)On residential areas attempt to minimize impact of the highway on residences e.g. depressed facility, increased buffer between highway and cluster of homes by adjusting the alignment

TR General guidelines - 4 9)Design the alignment to enhance scenic views like rivers, rock formations, outstanding structures and parks. Review Exhibits 3.81 in the text book (The Green Book)

TR Design Exercise 2 Given topographic map with existing features and part of completed design (A and B) To develop two alternatives –Alternative One – use existing road but upgraded to multilane (dual carriageway) –Alternative 2 – Cross the existing road at one point only

TR The process Development of Design standards –Volume – for the new road projected ADT 14,000 vpd and for existing road is 3000 vpd –With 20% truck and buses and diretional distribution is 60:40 –Road function: Mobility road – rural arterial –Terrain – Check no. of contours crossed per Km (#ORN 6)

TR Adopted standards Pavement type: AC Design Speed 120 Km/h for flat terrain Width: lane Shoulder :Gravel shoulder 2.5 m wide Cross slope: 2%Shoulder 4% Max. Grade: Need for climbing lanes:

TR Minimum radius: e design = 6%; R min = Minimum K value = Minimum SSD required Provided*