Your firm is designing an uncurbed urban collector for TxDOT with an estimated A

ID: 2312373 • Letter: Y

Question

Your firm is designing an uncurbed urban collector for TxDOT with an estimated ADT of 20,000 vehicles per day. Your intern makes the first attempt at design, but "he ain't from around here". Which of the following design choices need revision, and what would you recommend they be changed to. Use either desirable or minimum values, but be consistent Clear zone: 10 ft Travel lanes: 9.5 ft inside lanes, 10.5 Shoulder: 2 ft. Sidewalk: 3.5 ft, adjacent to shoulder Foreslope: 1:3 Backslope: 1:2 12 ft median with trees outside lanes

Explanation / Answer

For an Uncurbed Urban Collector for TxDOT with an estimated ADT of 20000 vehicles per day the given parameters are revised as follows:

1. Clear zone: For design speed greater than or equal to 50 mph - Minimum is 20 ft

Desirable is 30 ft

For design speed less than or equal to 45 mph – 10 ft is considered

2. Travel lanes: Minimum width – 10 ft

Desirable width – 12 ft

3. Shoulder: Minimum width –3ft

Desirable width – 8ft

4. Side walk: Minimum width – 5 ft

Desirable width – 6-8 ft

5. Fore slope: Typical fore slope used is 1V: 6H

(When front slope is steeper than 1:3 a longitudinal barrier maybe considered to keep vehicles from traversing the slope. Also recovery is less likely on 1:3 and 1:4 slopes)

6. Back slope: Typical back slope used is 1V:4H

(If steep front slopes are provided the back slopes considered should be flatter and vice versa)

7. Median:

For Single Left Turn Lane – 16 ft median width is considered ( 12ft lane + 4ft divider(trees))

For Two Way Left Turn Lane:

Design Speed (mph)

Width of Two Way Left Turn Lane (ft)

Desirable Values

Minimum Values

Less than or equal to 40

12-14

45-50

Greater than 50