Work Zone Mobility and Safety Program
Photo collage: temporary lane closure, road marking installation, cone with mounted warning light, and drum separated work zones.
Office of Operations 21st Century Operations Using 21st Century Technologies

Text from 'Traffic Impacts of Short Term Interstate Work Zone Lane Closures: The South Carolina Experience' PowerPoint Presentation

Slide 1

Traffic Impacts of Short Term Interstate Work Zone Lane Closures: The South Carolina Experience

Wayne Sarasua, Ph.D., P.E.

sarasua@clemson.edu

Slide 2 and 3

Overall Goals

  • Develop a means to determine an actual volume of vehicles per hour per lane to be used to determine when lane closures may be permitted.
  • Develop a means to estimate speeds, delays, and queue lengths due to short-term lane closures in work zones
  • Analyze the effects of roadway grades, truck percentages, and lane widths on work zone traffic characteristics when lane closures are present

Slide 4

Research Participants

  • Clemson University: Wayne Sarasua, David Clarke, and several GRAs
  • The Citadel: William J. Davis

Slide 5

Knowledge Acquisition and Literature Review

  • Strategy sessions
  • Comprehensive Literature Review
  • Survey of State DOTs

Slide 6

Classical Traffic Flow Theory

Diagram: Illustrates that for traffic flow to stay constant, the density of the road must increase in proportion to the decrease in speed.

Slide 7

Capacity Measurement

  • Maximum rate of flow (HCM)
  • Mean queue discharge rate
  • Hourly rate of flow under congested conditions
  • Flow rate at which traffic changes from uncongested to queued conditions

Slide 8

Traffic Measurement Techniques

  • Traffic Volume/Headway: Video surveillance, Inductive loops with counters, Road tubes with counters, and Inductive counters
  • Speed measurement: Road tubes and Radar or Laser

Slide 9

Factors Influencing Freeway Work Zone Capacity

  • Work zone configuration
  • Highway grade
  • Presence of freeway ramps
  • Traffic stream make-up
  • Weather conditions
  • Intensity/duration of construction activities
  • Lighting

Slide 10

Volume Thresholds

The following table shows the threshold lane volume for 7 states.

State Threshold Lane Volume
Connecticut 1,500 - 1,800 vphpl
Missouri 1,240 vphpl
Nevada 1,375 - 1,400 vphpl (7% trucks)
Oregon 1,400 - 1,600 pcphpl
South Carolina 800 vphpl
Washington 1,350 vphpl
Wisconsin 1,600/2000 pcphpl (rural/urban)

Slide 11

Instrumentation and Field Data Collection

  • Design the surveillance setup, acquire hardware, and implement design
  • Field test and make adjustments
  • Field test at an actual interstate work zone
  • Collect data at various rural and urban work zone sites

Slide 12

Photo: Wind Research Tower

Slide 13

Surveillance Setup

Illustration: Tall tripods from SkyEye Corporation. One surveillance camera is pointed toward the flow of traffic; the other is pointed toward the Work Zone limits

Slide 14

Photo: Roadside Setup. Surveillance camera set up on tripod pointed toward flow of traffic

Slide 15

Photo: Base of tripod

Slide 16

Photo: Workers set up connecting cables on surveillance camera

Slide 17

Photo: Autoscope camera and pan/tilt unit

Slide 18

Photo: Workers raise the autoscope camera and pan/tilt unit on tripod

Slide 19

Photo: Tie-down and ground anchor for the tripod

Slide 20

Photo: Raised tripod

Slide 21

Photo: Tripod set up on a bridge

Slide 22

Photo: Great perspective view: a clear view of the road from the perspective of the tripod

Slide 23

Photo: Peripheral devices

Slide 24

Surveillance Setup Summary

  • Tripods are of adequate (not optimal) height
  • Stable, even in windy conditions.
  • Very flexible
  • Enhanced safety
  • Little or no effect on traffic operations
  • Need about an hour to setup completely
  • Breakdown takes about 1/2 hour

Slide 25

Projects

  • Collected data at 22 locations
  • First data collection on 9/12/01
  • Summary: I-85: 13 Projects; I-26: 6 Projects; I-77: 1 Project; and I-385: 2 Projects

Slide 26

Work Zone Project Log

The table below lists projects by number; date; start time and end time; interstate, direction, and MPP location; type of work; closure geometry; taper length; equipment activity (heavy or light); length of work (short or long), and weather conditions.

Project
No.
Date Time
start
Time
end
Location
Interstate
Location
Direction
Location
MPP
Type of work Closure geometry Taper length Equipment activity Length of Work Zone Weather conditions
1 09/12/01 19:15 21:15 85 N 32 Median Cable Guardrail Inside lane of 2 closed 863 Light Short Warm, Clear
2 09/13/01 19:45 20:45 26 W 54 Median Cable Guardrail Inside lane of 2 closed 795 Light Short Warm, Clear
3 09/16/01 19:40 21:15 85 S 8.5 Median Cable Guardrail Inside lane of 2 closed 600 Light Short Warm, Clear
4 09/30/01 19:05 22:30 85 N 0 Median Cable Guardrail Inside lane of 2 closed 665 Light Short Warm, Clear
5 10/01/01 9:00 18:00 77 N 80 Paving (OGFC) Inside 2 lanes of 4 closed 675, 1475, 850 Heavy Long Warm, Clear
6 10/03/01 17:00 22:30 385 N 40 Paving (surface) Outside lane of 2 closed 446 Heavy Long Warm, Clear
7 11/05/01 20:00 22:00 26 W 208 Final striping Outside 2 lanes of 3 closed 668, 1544, 684 Heavy Short Cold, Clear
8 01/31/02 15:30 16:00 26 E 178 Concrete Pavement Repair Outside lane of 2 closed 800 Heavy Medium Cool, Clear
9 03/11/02 16:00 18:10 385 W 2 Median Cable Guardrail Inside lane of 2 closed 950 Light Long Cool, Clear
10 04/03/02 8:30 10:30 26 E 104 Median Cleanup Inside lane of 3 closed Light Short Warm, Clear
11 04/08/02 8:42 11:10 26 E 107 Median Cleanup Inside lane of 4 closed 575 Light Short Warm, Clear
12 06/03/02 19:00 21:15 85 S 28 Paving Inside lane 1 of 3 closed 800 Light empty cell Clear
13 06/04/02 19:00 20:30 85 S 28 Rumble Strips Inside lane 1 of 3 closed Light empty cell Clear
14 06/06/02 19:00 19:00 85 S 28 empty cell Inside lane 2 of 3 closed 800 Light empty cell Clear
15 06/07/02 empty cell empty cell 85 S empty cell NA NA NA NA NA Rain
16 06/13/02 19:00 21:00 85 S 28 empty cell empty cell Inside 1 lanes of 2 closed empty cell Heavy empty cell empty cell Warm, Clear
17 06/14/02 19:00 21:20 85 S 28 Concrete Paving Outside lane of 2 closed Heavy Long Warm, Clear
18 06/20/02 20:00 22:00 85 S 28 Concrete Paving Outside lane of 2 closed 800 Heavy Long Warm, Clear
19 07/09/02 19:15 20:15 85 S 2 Bridge Maintenance Outside lane of 2 closed empty cell Light Long Warm, Clear
20 07/21/02 19:03 21:08 85 N 179 Bridge Maintenance Outside lane of 2 closed empty cell Light Long Warm, Clear
21 07/22/02 18:56 20:30 85 N 179 Bridge Decil Maintenance Outside lane of 2 closed empty cell Light Long Clear
22 08/23/02 21:00 22:00 26 W empty cell Concrete Paving Outside 2 lanes of 3 closed 800 Light Long Clear

NA=Data collection canceled due to weather conditions, after completion of equipment set-up.

Slide 27

Work Zone Project Summary Statistics for Vehicles

The table below lists statistics for vehicles including location, PC%, T%, minimum and maximum hourly volume, whether there is a queue, and the length of the queue.

Project
No.
Location PC% T% 1-minute hourly volume (max) 1-minute hourly volume (min) 5-minute hourly volume (max) 5-minute hourly volume (min) Hourly volume (max) Hourly volume (min) Queue? Max Queue Length
1 I-85 N MPM32 64.33% 35.67 1980 60 1056 648 empty cell None
2 I-26 W MPM 54 71.05% 28.95 1320 120 648 324 497 445 None
3 I-85 S MPM 8.5 87.25% 12.75 2160 300 1572 636 1221 767 Few 3200
4 I-85 N MPM 0 82.63% 17.37 2100 120 1440 324 1320 995 Continuous >1 mile
5 I-77 N MPM 80 84.56% 15.44 1410 450 1140 636 930 802 None
6 I-385 N MPM 40 96.83% 3.17 1140 120 744 60 553 458 None
7 I-26 W MPM 208 87.62% 12.38 1800 360 1308 576 1124 735 None
8 I-26 E MPM 178 84.45% 15.55 1680 360 1128 720 927 871 None
9 I-385 N MPM 2 84.49% 15.51 1320 0 696 276 565 509 None
10 I-26 E MPM 104 88.68% 11.32 2280 1140 2016 1266 1041 1041 Continuous >4500
11 I-26 E MPM 107 91.06% 8.94 1722 678 1480 1044 1308 1152 None
12 I-85 S MPM 28 68.61% 31.39 1740 180 1284 636 1090 820 None
13 I-85 S MPM 28 72.68% 27.32 2220 180 1668 756 1251 976 Discontinuous 500
14 I-85 S MPM 28 73.69% 26.31 2100 480 1524 1008 1357 1141 Discontinuous 8000
16 I-85 S MPM 28 73.42% 26.58 2160 540 1500 936 1341 1047 Discontinuous >1 mile
17 I-85 S MPM 28 82.79% 17.21 2280 120 1680 660 1504 1240 Continuous >1 mile
18 I-85 S MPM 28 69.67% 30.33 1800 360 1452 732 1110 916 Continuous 3000
19 I-85 S MPM 02 66.93% 33.07 1800 240 1236 636 672 672 None
20 I-85 N MPM 179 85.96% 14.04 1980 120 1032 648 903 799 Continuous >1mile
21 I-85 N MPM 179 65.57% 34.43 1800 300 1548 384 1339 867 None
22 I-26 W 90.40% 9.60 2100 420 1104 948 920 131 Discontinuous empty cell
Average empty cell 79.65% 20.35 1852 317 1298 660 1049 819 empty cell empty cell

Work Zone Project Summary Statistics for Passenger Car Equivalents

The table below lists statistics for passenger car equivalents, including location, PC%, T%, minimum and maximum hourly volume, whether there is a queue and the length of the queue.

Project
No.
Location PC% T% 1-minute hourly volume (max) 1-minute hourly volume (min) 5-minute hourly volume (max) 5-minute hourly volume (min) Hourly volume (max) Hourly volume (min) Queue? Max Queue Length
1 I-85 N MPM32 64.33% 35.67 3060 60 1560 1044 empty cell None
2 I-26 W MPM 54 71.05% 28.95 1680 180 882 492 702 640 None
3 I-85 S MPM 8.5 87.25% 12.75 2700 300 1824 726 1414 918 Few 3200
4 I-85 N MPM 0 82.63% 17.37 2280 120 1728 534 1540 1243 Continuous >1 mile
5 I-77 N MPM 80 84.56% 15.44 1770 555 1389 765 1112 954 None
6 I-385 N MPM 40 96.83% 3.17 1500 120 768 60 572 479 None
7 I-26 W MPM 208 87.62% 12.38 2160 360 1506 666 1310 871 None
8 I-26 E MPM 178 84.45% 15.55 2010 450 1416 864 1107 1059 None
9 I-385 N MPM 2 84.49% 15.51 1710 0 918 312 689 608 None
10 I-26 E MPM 104 88.68% 11.32 2565 1245 2262 1446 1178 1178 Continuous >4500
11 I-26 E MPM 107 91.06% 8.94 1968 738 1620 1152 1437 1284 None
12 I-85 S MPM 28 68.61% 31.39 2520 180 1758 1056 1518 1217 None
13 I-85 S MPM 28 72.68% 27.32 3510 270 2232 960 1640 1428 Discontinuous 500
14 I-85 S MPM 28 73.69% 26.31 2790 660 2202 1428 1836 1574 Discontinuous 8000
16 I-85 S MPM 28 73.42% 26.58 2790 210 2100 1296 1844 1441 Discontinuous >1 mile
17 I-85 S MPM 28 82.79% 17.21 2640 120 2070 768 1793 1564 Continuous >1 mile
18 I-85 S MPM 28 69.67% 30.33 2550 450 1998 1056 1552 1331 Continuous 3000
19 I-85 S MPM 02 66.93% 33.07 2070 330 1674 930 995 995 None
20 I-85 N MPM 179 85.96% 14.04 2670 210 1500 978 1332 1198 Continuous >1mile
21 I-85 N MPM 179 65.57% 34.43 2190 360 1830 558 1536 1065 None
22 I-26 W 90.40% 9.60 2550 420 1338 1110 1038 149 Discontinuous empty cell
Average empty cell 79.65% 20.35 2366 349 1646 867 1307 1060 empty cell empty cell

Slide 28

Data Collection

  • Night time data collection not ideal: Autoscope is not as effective and volumes are generally low except I-85
  • Difficult to obtain specific information on location of closure in advance
  • Setup and procedures adequate for providing data to meet project objectives

Slide 29

Data Analysis

  • Graph and analyze data
  • Develop predictive model as a function of known model parameters: Traffic and truck volumes, Length of lane closure, Lane widths, Shoulder characteristics, and Roadway grades

Slide 30

Underlying Concepts

Equation 1: k=q/s

where:

k = density (vehicles per mile)

q = flow (vehicles per hour)

s = speed.(mph)

Can also be expressed in terms of average vehicle spacing:

Equation 2: k=5280/spacing

Slide 31

An Example of Capacity

Given:

Speed limit for short term work zone projects in South Carolina is 45 mph.

Average spacing in saturated conditions for a speed of 45 mph is 150 feet per vehicle.

Using equation 2, k  =  5280/spacing  =  35.2 vehicles per mile.

From equation 1, q = ks = 35.1 * 45 = 1584 vehicles per hour.

Slide 32

Diagram from the Classical Traffic Flow Theory, for flow to stay constant, the density of the road must increase in proportion to the decrease in speed.

This indicates that at lower speeds, there is willingness for cars to travel at closer intervals. The table below indicates the speed in miles per hour and spacing of the traffic flow.

Speed Spacing
45 150
40 133
35 117
30 100
25 83
20 67
15 50
10 33

Slide 33

Combining Data to Facilitate Analysis

  • No single project completely follows Greenshields' generalized form
  • Necessary to combine data
  • Difficult to isolate the characteristics of individual projects
  • Underlying assumption that all projects that were combined were homogeneous

Slide 34

Project Characteristics

  • Commonality: Rolling terrain except I-26 south of Columbia, 12-foot lane widths, Similar taper lengths
  • Differences: Type of maintenance activities, Work zone length, and Number of lanes downstream

Slide 35

Speed versus Flow: 2 to 1-lane

Scatter graph showing discrete 5-minute traffic flows.

With the mean speed at 45 miles per hour, traffic flow ranges from 400 to 1600 vph.

With the mean speed at 20 miles per hour, traffic flow ranges from 1000 and 1600 vph.

Slide 36

Speed versus Flow: 2 to 1-lane

Scatter graph showing 12 consecutive 5-minute periods.

With the speed ranging from 10 to 50 miles per hour, traffic flow ranges only slightly, from 1000 to 1400 vph.

Slide 37

Considering Heavy Vehicles

  • Research has shown that heavy vehicles have a significant effect on capacity
  • Must be considered on a case by case basis
  • Most common approach is applying passenger car equivalents (PCE)

Slide 38

Methodology for Determining PCE

  • Measured headways by analyzing video
  • Used software developed for project (Satflo2) to record time and vehicle type
  • Results are tabulated and graphed

Slide 39

Headway Frequencies by Vehicle Type

Bar chart: The trend line shows the number of headway occurrences increases dramatically (up to 65) in the first half-hour, decreases (down to 50) over the next half-hour, and then increases again (up to 85) after 1.5 hours. From there, the headway occurrences drop significantly (down to 35) at 2 hours and continue to decrease (with minor increases) through the 10 hours, with only 2 occurrences at hour 10.

Slide 40

Passenger Car Equivalents Grouped by Speed

The table below lists statistics for passenger car equivalents (RVs and trucks) grouped by speeds of less than 15 miles per hour, between 15 and less than 30 mph, between 30 and less than 45 mph, between 45 mph and less than 60 mph, and greater than 60mph.


Project

RV less than 15mph

Truck less than 15mph

RV 15 to less than 30mph

Truck 15 to less than 30mph

RV 30 to less than 45mph

Truck 30 to less than 45mph

RV 45 to less than 60mph

Truck 45 to less than 60mph

RV greater than 60mph

Truck greater than 60mph

13

0

0

1.52

1.68

1.28

1.66

1.4

1.75

1.11

1.79

14

1.32

1.89

1.62

2.06

1.39

2.14

1.66

1.92

1.52

1.85

16

0

0

1.23

2.42

1.5

2.14

1.44

2.14

1.26

2.06

17

1.2

2.09

1.33

2.22

1.5

2.48

1.67

2.75

0

0

18

1.37

2.04

1.42

2.03

1.6

1.95

1.41

2.02

1.44

2.12

20

1.68

2.21

1.59

2.2

1.98

2.18

1.28

2.02

1.7

2.62

21

0

0

0

1.27

1.95

1.98

1.58

1.85

1.22

1.91

7

0

0

0

0

1.58

2.01

0

0

0

0

10

0

0

1.16

2.13

1.16

1.89

1.06

0

0

0

11

0

0

0

1.83

0

0

1.46

1.87

1.15

2.2

5

0

0

0

0

1.4

1.86

0

0

0

0

All

1.414

1.948

1.414

2.085

1.497

1.986

1.511

1.940

1.375

1.991

Slide 41

Average Passage Car Equivalents (PCEs) Used in Analysis

The table below provides the number of sample passenger cars, RVs, and heavy trucks used in this study.

Type of Vehicle Sample Passenger Car Equivalent
Passenger Car 10293 1.00
RV 470 1.44
Heavy Truck 2019 1.93

Slide 42

Speed versus Flow: 2 to 1-lane

Scatter graph showing discrete 5-minute passenger car equivalents.

With the mean speed at 45 miles per hour, flow (pcph) ranges from 500 to 1700 vph. With the mean speed at 20 miles per hour, flow (pcph) ranges from 1200 and 1600 vph.

Slide 43

Speed versus Flow: 2 to 1-lane

Scatter graph showing 12 consecutive 5-minute periods (passenger car equivalents).

With the speed ranging from 10 to 50 miles per hour, flow ranges from 800 to 1700 vph.

Slide 44

Modeling Methodology

  • Model Speed versus Density Relationship
  • From the resulting linear model, substitute k=q/s
  • Determine maximum Flow in PCE
  • Adjust for other factors
  • Formulate model for application to specific short-term work zones

Slide 45

Speed versus Density: 2 to 1-lane

Scatter graph showing discrete 5-minute passenger car equivalents.

Speed= -0.3951 (Density) + 52.539

R squared (R2) = 0.8114

With the mean speed at 50 miles per hour, density ranges from 20 to 50 pcpmi.

With the mean speed at 10 miles per hour, density ranges from 60 and 150 pcpmi.

Slide 46

Speed versus Density:  2 to 1-lane

Scatter graph showing 12 consecutive 5-minute periods (passenger car equivalents).

Speed= -0.4931 (Density) + 54.108

R squared (R2) = 0.9536

With the speed ranging from 15 to 50 miles per hour, density ranges from 15 to 80 pcpmi.

Slide 47

Modeling Speed versus Flow

s = -0.395 k + 52.54 (5-minute discrete data)

s = -0.493 k + 54.11 (5-minute consecutive data)

Substituting k=q/s gives:

q= -2.53 s2 + 133 s (5-minute discrete data)

q= -2.03 s2 + 110.7 s (5-minute consecutive data)

where: q = flow (pcphpl)

s = speed (mph)

Slide 48

Speed versus Flow: 2 to 1-lane

Scatter graph showing discrete 5-minute passenger car equivalents.

With the mean speed at 50 miles per hour, flow ranges from 500 to 1700 pcph.

With the mean speed at 10 miles per hour, density ranges from 1000 and 1700 pcph.

Slide 49

Speed versus Flow: 2 to 1-lane

Scatter graph showing 12 consecutive 5-minute periods (passenger car equivalents).

With the speed ranging from 10 to 45 miles per hour, flow ranges from 600 to 1700 pcph.

Slide 50

Estimating Capacity

First derivative of the s versus q model is slope of the parabola

dq/ds = -5.06 s + 133               5-minute discrete data

dq/ds= -4.06 s + 110.7             5-minute consecutive data

Slope of the parabola at maximum flow = 0. Setting the above equations = 0 give the speeds at maximum flow.

Substituting into previous slide gives max flow (capacity):

1748 pcphl  (5-minute discrete data)

1483 pcphl  (5-minute consecutive data)

Slide 51

Considering Grades

  • HCM considers grades in calculating PCEs: We found little variation in PCEs
  • Most projects had rolling terrain with moderate grades rarely extending more than a 1/2 mile
  • We did do some stratification
  • HCM individual grade sections applicable

Slide 52

A Comparison of Stratified Data

Line graph: As speed decreases from 55 to 30 mph on I-85, flow increases from 0 to 1700 pcph. As speed further decreases from 30 mph to 5 mph on I-85, flow decreases from 1700 to 600 pcph.

As speed decreases from 50 to 25 mph on non I-85, flow increases from 0 to 1700 pcph

Slide 53

Considering Other Factors

  • Work zone activity - used regression models with dummy variables. Found no significance
  • Ramps - ramp volumes at sites with nearby on-ramps were typically low
  • Weather - adverse weather never experienced duringdata collection

Slide 54

Formulating Final Model - fHV

HCM heavy vehicle adjustment factor:

Equation 3: fHV=            1/1+[PT(ET-1) + PRV(ERV-1)]

where:

PT = proportion of trucks,

PRV = proportion of RVs and cars with trailers,

ET = PCEs for trucks and buses, and

ERV = PCEs for RVs and cars with trailers.

A first estimate of capacity (veh/hr/lane):

C' = 1480 *fHV

Slide 55

Accounting for Number Lanes

Data indicates that using a simple factor based on the number of discharge lanes is appropriate. The capacity estimate becomes:

C'' = 1480 *fHV * N

where:

C'' = C' adjusted based on the number of lanes open through the work zone (veh/hr) and N = number of lanes open through the work zone.

Slide 56

Accounting for Work Zone Activity

The HCM 2000 suggests adjusting base capacity up or down by 10% depending on whether or not the work zone activity is more or less than normal. Thus, final form becomes:

Equation 4: CWZ = (1480 + I) *fHV * N

where:

CWZ = the estimated capacity of a short-term work zone (veh/hr),

fHV= heavy vehicle adjustment factor,

N = number of lanes open through the work zone, and

Slide 57

Example

Given: planned 2 to 1-lane typical short-term lane closure

Peak volume of 1,100 veh/hour 18 % trucks, 2 % RVs

Should the closure be moved to the evening?

1. Calculate fHV:  Using PCE table, the ETand ERVare 1.93 and 1.44 respectively. Using equation 3, fHV  = 0.85.

2.Calculate CWZ: Assuming I = 0 for a typical closure and N= 1, using equation 4 yields CWZ = 1,258 vehicles per hour.

3. Compare volume to capacity: the V/Cratio in this example works out to be 0.87 based

It is unlikely that the volume will reach capacity.

Slide 58

Rate of Queue Development

Equation 5: sw = q2-q1/k2-k1

where:

swis the shock wave velocity (will be negative),

q2is the discharge flow,

q1demand flow (flow upstream of the work zone),

k2density of the flow of the moving queue, and

k1density of the flow before the queue.

Slide 59

Queue Example

Given: 2 to 1-lane short-term lane closure. Before the closure, volume is 1,500 vehicles per hour and the density is approximately 25 vehicles per mile. Work zone causes the flow to reduce to 1,000 vehicles per hour and a queue density of 100 vehicles per mile. What would the queue length be from the bottleneck 5 minutes after the queue initially forms?

Shock wave velocity = (1000-1500)/(100-25) = -6.7 mph.

After 5 minutes: -6.7mph * 5 min * 1hr/60 min = 0.56 miles. At 100 vehicles per mile, this would equal 56 vehicles in the queue.

Slide 60

Graphical Example

Diagram: Illustration of the above calculation. With volume at 1,500 vehicles per hour and with the flow reduced to 1,000 vehicles per hour, the queue length from the bottleneck 5 minutes after the queue initially formed would be 56 vehicles.

Slide 61

If the volume is below capacity, no queue will form.

If the volume exceeds capacity, two speeds are assumed:

< 100 pcphpl over capacity, speed is 35 mph

> 100 pcphpl over, speed drops to 15 mph

The density for different speeds in PCEs/mile is given by:

k= (s-54.1)/-0.493

Thus, k= 80 PCEs per mile at a speed of 15 mph. Because q=k*s, the discharge flow is 1200 pcphpl. For a given work zone duration, length of the queue can be estimated in a similar fashion to the previous example.

Slide 62

Conclusions

  • Setup works well
  • Not enough data for conclusive findings on effects of various factors
  • Projects showed interesting traffic phenomena
  • 800 vphpl equates to 1232 pcphpl in the absolute worst case 30 % trucks with a PCE of 2.8. This is still more than 250 pcphpl less than the conservative base value (1480)
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