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Chapter 3 _2_

# Chapter 3 _2_ - the recommended design deceleration rate is...

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ECI 161 Winter 2012 Example 1 Due to crashes at a railroad crossing, an overpass (with a roadway surface 24 ft above the existing road) is to be constructed on an existing level highway. The existing highway has a design speed of 50 mph . The overpass structure is to be level , centered above the railroad, and 200 ft long. What length of the existing level highway must be reconstructed to provide an appropriate vertical alignment? 24 ft 200 ft Rail road Level road Plan View Profile View

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ECI 161 Winter 2012 2 An overpass is being built over the PVI of an existing equal-tangent sag curve. The sag curve has a 70 mph design speed, and G 1 = - 6%, G 2 = +3%. Determine: 1) The minimum necessary clearance height of the overpass 2) The resultant elevation of the bottom of the overpass over the PVI Example 2
3 A vertical curve was designed in 2005 for a design speed of 70mph to connect grades G1=+1.0% and G2=-2.0%. The curve is to be redesigned for a 70mph design speed in the year 2023. Vehicle braking technology has advanced such that

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Unformatted text preview: the recommended design deceleration rate is 25% greater than the value used to develop Table 3.1, but due to the higher percentage of older people in the driving population, design reaction times have increased by 20% . Also, vehicles have become smaller so that the drivers eye height is assumed to be 3.0ft above the pavement and roadway objects are assumed to be 1.0ft above the pavement surface. Compute the difference in design curve lengths. Example 3 ECI 161 Winter 2012 4 A highway reconstruction project is being undertaken to reduce crash rates. The reconstruction involves a major realignment of the highway such that a 60 mph design speed is attained. At one point on the highway, an 800ft crest vertical curve exists. Measurements show that at 3+52 stations from the PVC, the vertical offset is 3ft. Assess the adequacy of this existing curve in light of the reconstruction design speed of 60mph. Example 4...
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Chapter 3 _2_ - the recommended design deceleration rate is...

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