Practice Quiz

Civil Engineering PE

Category - Transportation

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What is the minimum spiral curve length transition for a new roadway with a radius of 1000 feet and a design speed of 45 miles per hour (mph), assuming a 2 ft/sec3 lateral acceleration increase rate?
  1. 143.5 feet
  2. 158.6 feet
  3. 229.2 feet
  4. 237.6 feet
Explanation
Answer: A - The minimum spiral curve length transition for a new roadway with a radius of 1000 feet and a design speed of 45 mph is 143.5 feet.

Solution: Use American Association of State Highway Transportation Officials (AASHTO)Equation for minimum length of spiral transition curve

Ls = 3.15 x (design speed)3/circular curve radius x maximum rate of change in lateral acceleration

Ls = 3.15 V3 / RC

Given, V = 45 miles per hour

R = 1000 ft

C = 2 ft/s3

Then Ls = 3.15 (45)3 / 1000(2) = 143.5 feet
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