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PE Civil Exam - Transportation > 9. Traffic Engineering (Capacity Analysis and Transportation Planning) > Flashcards

9. Traffic Engineering (Capacity Analysis and Transportation Planning) Flashcards

1
Q

What is capacity analysis?

A

How much traffic a given transportation facility can accommodate (quantitative measure of facility)

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2
Q

What is level of service?

A

How well the present traffic situation is on a given transportation facility (qualitative measure of facility) (i.e., quality of a given flow rate)

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3
Q

What is the base condition of a freeway or multilane highway and its criteria?

A

The full capacity of the roadway segment is achieved under good weather, good visibility, no incident/accidents, no work zones, and no pavement deterioration that affects operations.

Includes:

  • No heavy vehicles
  • Drive population composed of regular/familiar users of the facility
  • 12-ft lanes width and adequate lateral clearances.
  • Capacity under based conditions varies with Free Flow Speed (FFS).
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4
Q

In general, what is Free Flow Speed (FFS)?

A
  • the mean speed of passenger cars measured during period of low to moderate flow (up to 500pc/hr/ln). (i.e., average speeds are constant in this range of flow rates).
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5
Q

Describe the speed-flow curves for uninterrupted flow on basic freeway and multilane highways segments?

A
  • Constant Speed Range: the range of flow rates (pc/hr/ln) where the speed is constant. From flow rate 0 to BP; speed = FFS.
  • Decreasing Speed Range: speed decreases from FFS parabolically from BP to the capacity.
  • Capacity (c): occurs when the traffic stream density, D = 45 pc/mi/ln.
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6
Q

What is Freeway - FFS?

A

a theoretical speed when the density and flow rate on a FREEWAY are both zero. Expect to prevail at flow rates between 0 and 1000 pc/hr/ln

Sensitive to the following:

  • Lane Width
  • Lateral Clearances
  • Total Ramp Density (most critical)
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7
Q

What is Total Ramp Density (TRD) [Freeway]?

A

is the average number of on-ramps, off-ramps by direction per mile. Applies to a 6-mile segment of freeway (3 miles in each direction of the study). i.e., total number of ramps located between 3-miles upstream and 3-miles downstream of the midpoint of the segment divided by 6.

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8
Q

Equation for FFS for FREEWAY segment?

A

HCM Vol. 2 - Equation - 12-2; FFS = BFFS - f_LW - f_RLC - 3.22TRD^0.84

  • f_lw = lane width adjustment
  • f_rlc = right side lateral clearance
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9
Q

Equation for FFS for MULTILANE segment?

A

HCM Vol. 2 - Equation 12-3; FFS = BFFS - f_LW - f_TLC - f_M - f_A

  • f_TLC = total lateral clearance adjustment
  • f_M = median type
  • f_A = access point density
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10
Q

What is the default FFS for FREEWAY?

A

FFS = 75.4 mph

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11
Q

What is the default FFS for MULTILANE segment?

A

Design speed (if available) OR the posted/statutory speed limit: +5 mph for speed limits >= 50 mph and +7 mph for speed limits < 50 mph.

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12
Q

Process for solving Freeway/Multilane problems

A
  1. Calculate FFS: FREEWAY - Equation 12-2; MULTILANE - Equation 12-3
  2. Check for FFS adjustments: Exhibit 11-21 (FREEWAY only); otherwise 1.0 for both freeway and multilane.
  3. Calculate flow rate: Equation 12-9
  4. Calculate breakpoint volume: [1,000 + 40 x (75 - FFS_adj)] CAF^2 (1400 pc/hr/ln always for MULTILANE)
  5. Check V_p less than or equal to BP
  6. If V_p less or equal to BP then use FFS_adj in density equation, otherwise FFS_adj must be adjusted using Equation 12-1
  7. b. Calculate capacity, c: Equation 12-6 - c =2,200 + 10 x (FFS_adj - 50) and c_adj = c x CAF
  8. Calculate density: Equation 12-11: D=v_p/S
  9. Check Exhibit 12-15 for LOS
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13
Q

What factors affect the operation of a weaving segment?

A
  • Length: distance between the merge and diverge
  • Width: number of lanes within the weaving segment
  • Configuration: the way the entry and exit lanes are aligned.
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14
Q

How to calculate density in a weaving segment?

A

D = (V/N)/S
where:
V = sum of flow rates for weaving and non-weaving
N = no. of lane within the weaving segment
S = average speed of all vehicles in weaving segment; Equation 13-22

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15
Q

What HCM chapter covers freeway merge and diverge segments?

A

Chapter 14

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16
Q

What is the max capacity of a sidewalk?

A

23 p/min/ft

17
Q

What is the effective walkway width?

A

W_E = W_T - W_O
where:
W_T = total walkway width
W_O = sum of fixed objects effective widths and shy distances of linear features

18
Q

What is the effective length of a fixed object?

A

Assumed to be 5x the object’s effective width.

19
Q

What is the default pedestrian speed?

A

3.5 fps or 210 fpm

20
Q

What are the three accident categories?

A
  • Property damage only
  • Personal injury
  • Fatalities
21
Q

What is the accident ratio for intersection in RMEV?

A

R = (no. of accidents x 10^6)/[(ADT)(No. of years)(365)]

22
Q

What is the accident ratio for route segment in Hundred Million Vehicle Miles?

A

R = (no. of accidents x 10^8)/[ADT)(No. of years)(365)(L)]

23
Q

What is the conservation of momentum equation?

A

(M_v)(V_0) = (M_v + M_1) x V_1

24
Q

What is saturation flow at a signalized intersection?

A

the max throughput for the signalized intersection approach, if the approach was given a green light for a full hour. (S_h = saturation headway which is the min time headway, 2 sec.)

25
Q

What is the saturation flow amount under perfect conditions?

A

1900 vphgpl per HCM or 1800 vphgpl for 2s headways

26
Q

What is the equation for the capacity of an intersection approach?

A

c = N x s x g/C

27
Q

What is the volume-to-capacity ratio for an leg of an intersection?

A

is the lane group volume/its capacity: X = v/c; ideally c > v or X < 1

28
Q

How is the LOS of an intersection evaluated?

A

on the basis of control delay per vehicle (sec/veh.). Control delay is the portion of the total delay attributed to traffic signal operation. It includes initial deceleration delay, queue move-up time, stopped delay, and final acceleration delay.

d = d_1 (uniform control delay/uniform arrivals) + d_2 (incremental delay due to random arrivals) + d_3 (initial queue delay)

29
Q

How are Urban Street Segments characterized?

A
  • Travel speed

- Volume-to-capacity ratio for the thru movement at the downstream boundary intersection

30
Q

What factors influence mode choice?

A
  • Type of trip (purpose, time of time)
  • Trip maker (income, age, auto ownership)
  • System (travel times for different modes)
31
Q

What the the four trip assignment models?

A
  • Minimum Time Algorithms
  • All-or-Nothing
  • Capacity Restraint Assignment
  • Stochastic Equilibrium Assignment

PE Civil Exam - Transportation (18 decks)

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