2E. Traffic safety analysis

Question 1

How many conflict points are in a 4 leg intersection?

Answer 1

32 conflict points
- 8 diverging
- 8 merging
- 16 crossing

Question 2

How many conflict points are in a T intersection?

Answer 2

9 conflict points
- 3 merging
- 3 diverging
- 3 crossing

Question 3

How many conflict points are in a roundabout intersection?

Answer 3

8 conflict points
- 4 diverging
- 4 merging

Question 4

What is the formula for stopping sight distances on level grade?

Answer 4

SSD = 1.47Vt + 1.075(V^2/a)
t = brake reaction time (2.5 sec)
V = vehicle design speed (mph)
a = deceleration rate (Ft/sec^2) 11.2ft/sec^2 is default for AASHTO

Question 5

What are the 5 avoidance maneuvers when determining decision sight distance?

Answer 5

Avoidance maneuver A: stop on rural road; t= 3.0s
Avoidance maneuver B: stop on urban road; t=9.1s
Avoidance maneuver C; Speed/path/direction change on dual road; t=10.2-11.2s
Avoidance maneuver D; speed/path/direction change on suburban road; t=12.1-12.9
Avoidance maneuver E: speed/path/direction change on urban road; t = 14.0-14.5

Question 6

What is the formula for decision sight distance for maneuvers A & B

Answer 6

D = 1.47Vt + 1.075(V^2/a)

Question 7

What is the formula for decision sight distance for maneuvers C, D, E

Answer 7

D = 1.47Vt

Question 8

Where can passing sight distance information be found?

Answer 8

AASHTO 2018 section 3.2.4

Question 9

Where can Roadside barriers be found

Answer 9

AASHTO roadside design guide:
Chapters 5-7 for barrier systems
Chapters 9-10 for work zone and urban environments

Question 10

Where can end treatments considerations be found.

Answer 10

AASHTO roadside design guide: chapter 8

Question 11

What formula is used for determining vehicles speed after impacting sand-filled plastic barrel.

Answer 11

V=(Mv x Vo) / (Mv + M1)
V= velocity after impact
Mv = mass of vehicle (lbs)
Vo = original impact velocity
M1 = mass of sand in first barrel