- Date:05 May 2020
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The purpose of this tutorial is to demonstrate the calculation of. superelevation rates at critical points along a roadway alignment. according to the standards specified in the Standard Drawings. RD11 SE 2A,RD11 SE 3A,Superelevation Calculation, Horizontal curves will no longer be identified by degree they will be identified by radius only. Standard Drawings RD11 LR 1 Urban and RD11 LR2 Rural contain tables for different design. speeds and number of lanes showing the superelevation rate e d associated with curve. radius One important thing to note that is different from the earlier standards is that for a. specific e d the radius shown is the minimum radius that can be used Also for a given radius. the corresponding super rate is the minimum that can be used. For example given a radius of 730 ft the corresponding super rate is 3 If the e d is to remain. at 3 any radius higher than 730 can be used If the radius is to remain at 730 any e d lower. than 3 can be used, The numbers that appear under the number of lanes are runoff lengths L R The total. transition length L is the length at which the transition from Normal Crown NC to full super. e d takes place,Superelevation Calculation, The formula for the total transition length is found on Standard Drawing RD11 SE 1. Standard Drawing RD11 SE 2 shows the relationship of L to the begin and end points of the. horizontal curve,Superelevation Calculation, For a simple curve half of the transition length is before and half after the P C or P T. For a spiral curve L is the same as the length of the spiral. Standard Drawing RD11 SE 2A shows the lengths at which key points occur within the transition. Superelevation Calculation, Standard Drawings RD11 SE 3 and 3A contain the same information as RD11 SE 2 and 2A.

except for divided highways,Superelevation Calculation. 1 2 lane rural design,2 Design Speed 50 MPH,3 Curve Radius 2280 ft. According to Std Dwg RD11 LR 2 Minimum Runoff Lengths for Rural Highways the. superelevation rate e d for this curve is 4 6 046 ft ft 2280 ft is the minimum radius. that can be used with this rate This also means that for a particular e d rate a higher radius can. For instance according to the table a radius of 4400 ft can be used with a superelevation rate. of 4 6 Conversely for a radius of 2280 ft a superelevation rate of lower than 4 6 can be. In the table the runoff lengths are given For a rate of 4 6 and R 2280 the runoff length. L R is 110 feet for 2 lanes,Superelevation Calculation. In Std Dwg RD11 SE 1 the total transition length L is equal to L R L T where L T is the. Tangent Runout Length, According to the equation on RD11 SE 1 L T equals to 47 83 2 4 6 x 110 and the total. transition length L would be 110 47 83 157 83 rounded to 158 ft. Superelevation Calculation, Going back to RD11 LR 2 note 2 at the bottom of the sheet says that spirals are.

recommended for design speeds of 50 MPH or greater and superelevation of 3 or greater So. in our example L is also equal to spiral length,Superelevation Calculation. Plan view of proposed alignment,The alignment s beginning station is 100 00. The T S of the curve is at station 102 40 31,The S C of the curve is at station 103 98 31. The C S of the curve is at station 109 71 61,The S T of the curve is at station 111 29 61. The alignment s end station is 115 65 68,Superelevation Calculation.

The alignment starts out at normal crown at station 100 00. Normal Crown, The transition to superelevation will begin at the T S point station 102 40 31. The transition ends at the S C point station 103 98 31 This in the station at which full. superelevation begins,Full Superelevation,Superelevation Calculation. In the transition area a couple of key points to know are the Reverse Crown station and the. Remove Adverse Crown station, Going from Normal Crown to Full Super the point Remove Adverse Crown point will occur first. Remove Adverse Crown, Since the roadway curves to the left the pavement transitions from a negative cross slope to a. positive cross slope only on the right side therefore zero cross slope would only be on the right. side According to RD11 SE 2A this point occurs at the distance L T from the S C station or. 10240 31 47 83 10288 14 or station 102 88 14,Reverse Crown.

Also from RD11 SE 2A Reverse Crown occurs at S C L T x 2 or. 10240 31 47 83 x 2 10335 97 or station 103 35 97,Superelevation Calculation. At the other end of the curve the alignment transitions from full super back to normal crown. The transition begins at the C S point station 109 71 61 and ends at the S T point station. 111 29 61 The Reverse Crown and Zero Cross Slope stations would be calculated in the same. manner as for the first transition and would occur in reverse order. Now let s pick some random stations and calculate the superelevation. This station occurs in the spiral portion of rthe alignment which is in the transition. The rate of change in superelevation is found by dividing the difference between normal crown. and full super by the transition length,For this example 046 020 158 066 158 0004177. L 10300 10240 31 59 69,59 69 x 0004177 025 or 2 5,Superelevation Calculation. This number is added to the cross slope at the beginning transition station 102 40 31 which is. normal crown 2, Since this number is less than 2 and has not yet reached reverse crown the other side will. Station 107 00 is in the full super area between the S C and C S 4 6 in this example. This station is in the transition from full super to normal crown 109 71 61 111 29 61 so. subtract the beginning station of the transition, 11000 10971 61 28 39 The rate of change is the same as for the transition at the beginning.

end of the curve 0004177,28 39 x 0004177 0119 or 1 19. This number is subtracted from the full super rate at 109 77 61 4 6 1 19 3 41. Superelevation Calculation, For curves where a spiral is not required the calculation methods are the same The calculated. transition lengths are spaced so that the P C and P T points are at the halfway point of L. Superelevation Calculation Going back to RD11 LR 2 note 2 at the bottom of the sheet says that spirals are recommended for design speeds of 50 MPH or greater and superelevation of 3 or greater

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