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Speed Analysis

This chapter describes the speed metrics used to assess the effectiveness of the SDCWS. Since data were collected at three locations per curve, results for individual sites are summarized.

Speed Metrics

The change in speed from the before period was compared to each after period. A negative result indicates that speeds were reduced from the before period to the after period. A positive value indicates that speed increased from the before period to the after period. Mean and 85th percentile speeds are shown using a trend line. This is shown for graphical purposes only and should not be interpreted to indicate that speeds can be interpolated between data collection periods.

The change in mean and 85th percentile speed from the before period speed to specific after period speed are shown in miles per hour (mph). The percentage change in the fraction of vehicles exceeding the posted or advisory speed is also presented. A number of speed metrics were calculated for the direction of travel towards the signs. They include average speed, standard deviation (SD) of speed, 50th percentile speed, 85th percentile speed, and number of vehicles traveling 5, 10, 15, or 20 mph over the posted or advisory speed limit. For simplicity in setting up the pneumatic road tubes, the traffic counters were set up to record both directions of traffic on the two-way roadway. Results were reduced by lane and are only presented for traffic traveling in the direction of the SDCWS.

Results to Date

This interim report does not provide a commentary on the results to date. Tables 5 and 6 provide a summary of speed statistics across all sites at both PC and CC. The table shows the changes from before to 1 month after, with a negative sign showing a reduction in speed or percentage. Appendix contains the full data set collected before installation and 1 month after installation, in both tabular and graphic formats. The schedule of the data collection for each State is provided in table 7. This shows both data that have been collected and what will be collected in the future.

Table 5. Summary of results at point of curvature after 1 month.

State

IA

MO

TX

WA

WI

Road

Hwy
144

Hwy
221

FM
109

FM
407

FM
530

FM
1488

SR
7

SR
9

SR
203

Hwy
20

Hwy
67

Hwy
213

Posted Speed

55

55

60

55

60

55

50

55

55

55

55

55

Curve Advisory Speed

45

40

35

40

-0.9

40

20

40

None

30

25

50

Change in mean speed (mph)

-1.5

-1.5

-0.8

-1.8

-2

-2.4

-2.8

-1.4

-2

-1.8

-1.6

-0.7

Change in 85th percentile speed(mph)

-1

-1

-1

-2

-2.6

-3

-3

-1

-2

-2

-1

0

Change in Fraction of vehicles exceeding posted or advisory speed by

5 mph

-19.7%

-6.4%

-2.2%

-6.7%

-20.3%

-8.5%

-7.3%

-30.4%

-2.1%

-9.1%

0.0%

-9.5%

10 mph -33.3% -17.1% -8.8% -20.9% -36.4% -27.1% -30.0% -50.0% -14.5% -19.0% -3.1% -25.0%
15 mph 0.0% -32.0% -23.3% -41.9% -63.6% -53.6% -51.4% -100.0% -46.5% -40.7% -8.0% 0.0%
20 mph 0.0% -50.0% 0.0% 0.0% 0.0% 0.0% -77.8% 0.0% -62.5% -57.1% -21.5% 0.0%

 

Table 6. Summary of results at center of curve after 1 month.

State

IA

MO

TX

WA

WI

Road

Hwy
144

Hwy
221

FM
109

FM
407

FM
530

FM
1488

SR
7

SR
9

SR
203

Hwy
20

Hwy
67

Hwy
213

Posted Speed

55

55

60

55

60

55

50

55

55

55

55

55

Curve Advisory Speed

45

40

35

40

35

40

20

40

None

30

25

50

Change in mean speed (mph)

-2.1

0.3

-1.4

-1.1

-2

-0.1

-1.4

-0.9

-0.1

-1.8

-1.8

-1

Change in 85th percentile
speed (mph)

-2

0

-2

-2

-2.6

0

-1

-1

0

-2

-2

-1

Change in fraction of vehicles exceeding posted or advisory speed by

5 mph

-38.1%

0.0%

-5.7%

-8.2%

-20.3%

-4.8%

-19.0%

-26.3%

0.0%

-18.2%

-2.1%

-11.9%

10 mph

-58.3%

10.5%

-27.7%

-29.7%

-36.4%

2.5%

-45.0%

-33.3%

-2.8%

-45.5%

-11.6%

-20.0%

15 mph

0.0%

28.6%

-51.4%

-60.0%

-63.6%

0.0%

0.0%

0.0%

-4.0%

-66.7%

-28.3%

50.0%

20 mph

0.0%

0.0%

0.0%

0.0%

0.0%

0.0%

0.0%

0.0%

0.0%

-100.0%

-46.7%

0.0%

 

Table 7. Schedule of activities, all sites.

Activity Description

Schedule (Week)

Status

Before data collection

 

Complete

Washington

7/17/2012

Wisconsin

5/21 2012

Missouri

6/13 2012

Texas

6/25 and 7/9 2012

Iowa

8/29 2013

Installation

 

Complete

Washington

8/1/2012

Wisconsin

6/11 2012

Missouri

6/25 2012

Texas

7/16/2012

Iowa

9/10 2012

1-month after data collection

 

Complete

Washington

9/12/2012

Wisconsin

7/9 2012

Missouri

8/1 2012

Texas

9/3, 9/10,/9/24 2012

Iowa

10/10 2012

12-month after data collection

   

Washington

August 2013

 

Wisconsin

June 2013

 

Missouri

July 2013

 

Texas

June/July 2013

 

Iowa

September 2013

 

18-month after data collection

   

Washington

February 2014

 

Wisconsin

December 2013

 

Missouri

January 2014

 

Texas

December 2013/January 2014

 

Iowa

March 2014

 

Before Crash data collection

   

Washington

April 2013

 

Wisconsin

May 2013

 

Missouri

February 2013

 

Texas

TBD

 

Iowa

February 2013

 

After Crash data collection

   

Washington

April 2014

 

Wisconsin

May 2014

 

Missouri

September 2013

 

Texas

TBD

 

Iowa

February 2014

 

First Year Evaluation

12/31/2013

 

Final Report

8/31/2014

 

Appendix A. Baseline Data For each Test Section

Hwy 144(IA) - Eastbound Before
Composite image: Iowa Highway 144 eastbound before implementation, showing table data pointing to map for counter number, direction, start time, end time, and duration stopwatch for upstream, point of curvature, and center of curve
Figure 16. Photo. Iowa Highway 144 before data collection.

 

Hwy 144(IA) - Eastbound 1 Month After
Composite image: Iowa Highway 144 eastbound 1 month after implementation, showing table data pointing to map for counter number, direction, start time, end time, and duration stopwatch for upstream, point of curvature, and center of curve
Figure 17. Photo. Iowa Highway 144 1 month after data collection.

 

Hwy 144(IA) - Eastbound
Map: Iowa Highway 144 site layout showing locations of no passing sign and curve warning sign before curve on opposite sides of the road
Figure 18. Photo. Iowa Highway 144 site layout.

Iowa 144
Date: 8/29-8/30/2012
Period: Before

 

location (gps at center of curve)

2-12' lanes

# lanes and width

Left

curve direction (left or right)

Gravel 4'

shoulder type and width

45

posted speed of curve in each direction

55

tangent speed in each direction

55

advisory speed in each direction

See below

grade (average of 3 readings and list if positive or negative)

See below

super elevation

See Layout

location and type of signing before and in the

Asphalt

pavement type and condition

None

presence and location of street lighting

 

Grade

Begin S-N

Center W-E

End W-E

EB

Center

WB

Average

EB

Center

WB

Average

EB

Center

WB

Average

-.4

-.1

-.2

-.23

-0

-.9

-.4

-.43

-.6

-.5

-.8

-.63

 

Super Elevation

Begin W-E

Center S-N

End S-N

EB

Center

WB

Average

EB

Center

WB

Average

EB

Center

WB

Average

-5.3

-3.7

-4.9

-4.63

-8.5

-7.1

-7.4

-7.67

-1.2

+1

-1.4

-.53

Figure 19. Chart. Iowa Highway 144 site information.

 

Hwy 221 (MO) - Northbound Before
Composite image: Missouri Highway 221 northbound before implementation, showing table data pointing to map for counter number, direction, start time, end time, and duration stopwatch for upstream, point of curvature, and center of curve
Figure 20. Photo. Missouri Highway 221 before data collection.

 

Hwy 221 (MO) - Northbound 1 Month After
Composite image: Missouri Highway 221 northbound 1 month after implementation, showing table data pointing to map for counter number, direction, start time, end time, and duration stopwatch for upstream, point of curvature, and center of curve
Figure 21. Photo. Missouri Highway 221 1 month after data collection.

 

Hwy 221 (MO) - Northbound
Map: Missouri Highway 221 site layout showing curve warning with advisory speed southbound between the second and third chevron, a driveway in the study direction directly before the curve, and a curve warning with advisory 40 mile per hour speed in the study direction
Figure 22. Photo. Missouri Highway 221 site layout.

Missouri 221
Date: 6/13-6/1/2012
Period: Before

N42°31.432' W088°58.944'

location (gps at center of curve)

2 Lanes, 22' Asphalt

# lanes and width

Right

curve direction (left or right)

4' Asphalt Right

4' +3' Asphalt Left sharp drop

shoulder type and width

55

posted speed of curve in each direction

55

tangent speed in each direction

40

advisory speed in each direction

See Below

grade (average of 3 readings and list if positive or negative)

See Below

super elevation

See Layout

location and type of signing before and in the

Asphalt, Good

pavement type and condition

None

presence and location of street lighting

 

Grade

Begin S-N

Center S-N

End W-E

NB

Center

SB

Average

NB

Center

SB

Average

NB

Center

SB

Average

-3.6

-3.3

-2.9

-3.27

-4.5

-4.4

-4.7

-4.53

-8.8

-9.1

-9.8

-9.23

 

Super Elevation

Begin W-E

Center S-N

End S-N

NB

Center

SB

Average

NB

Center

SB

Average

NB

Center

SB

Average

-4.2

-2.6

-1.2

-2.67

-8.6

-8.0

-6.0

-7.53

2.0

-0.7

-1.4

-.03

Figure 23. Chart. Missouri Highway 221 site information.

Washington SR9
Date 7/17 - 7/18, 2012
Period: Before
Composite image: Washington State Route 9 before implementation, showing table data pointing to map for counter number, direction, start time, and end time for upstream, point of curvature, and center of curve
Figure 24. Map. Washington State Route 9 before data collection.

 

Washington SR9
Date 9/12 - 9/13, 2012
Period: 1 Month After
Composite image: Washington State Route 9 1 month after implementation, showing table data pointing to map for counter number, direction, start time, and end time for upstream, point of curvature, and center of curve
Figure 25. Map. Washington State Route 9 1 month after data collection.

Washington SR 9
Date: 7/17-7/18/2012
Period: Before

 

location (gps at center of curve)

2 Lanes, 10' Each
CL Rumble 12" Wide

# lanes and width

Left

curve direction (left or right)

2' Asphalt Shoulder Both

shoulder type and width

50

posted speed of curve in each direction

50

tangent speed in each direction

40

advisory speed in each direction

See Below

grade (average of 3 readings and list if positive or negative)

See Below

super elevation

See Layout

location and type of signing before and in the

Asphalt

pavement type and condition

None

presence and location of street lighting

Figure 26. Chart. Washington State Route 9 site information.

 

Washington SR9
Date 7/17 - 7/18, 2012
Period: Before
Composite image: Washington State Route 203 before implementation, showing table data pointing to map for counter number, direction, start time, and end time for upstream, point of curvature, and center of curve
Figure 27. Map. Washington State Route 203 before data collection.

 

Washington SR203
Date 9/12 - 9/13, 2012
Period: 1 Month After
Composite image: Washington State Route 203 1 month after implementation, showing table data pointing to map for counter number, direction, start time, and end time for upstream, point of curvature, and center of curve
Figure 28. Map. Washington State Route 203 1 month after data collection

Washington SR 203
Date: 7/17-7/18/2012
Period: Before

 

location (gps at center of curve)

2 lanes with 12" CL Rumble, 11' NB Lane;
10.5' SB Lane

# lanes and width

Left

curve direction (left or right)

NB-4.5' Asphalt Shld

SB-8' Asphalt w/ 12" Rumble

shoulder type and width

55

posted speed of curve in each direction

55

tangent speed in each direction

None

advisory speed in each direction

See Below

grade (avg. of 3 readings and list if positive or negative)

See Below

super elevation

See Layout

location and type of signing before and in the

Asphalt

pavement type and condition

None

presence and location of street lighting

Figure 29. Chart. Washington State Route 203 site information.

Washington SR7
Date 7/17 - 7/18, 2012
Period: Before
Composite image: Washington State Route 7 before implementation, showing table data pointing to map for counter number, direction, start time, and end time for upstream, point of curvature, and center of curve
Figure 30. Map. Washington State Route 7 before data collection.

 

Washington SR7
Date 9/12 - 9/13, 2012
Period: 1 Month After
Composite image: Washington State Route 7 1 month after implementation, showing table data pointing to map for counter number, direction, start time, and end time for upstream, point of curvature, and center of curve
Figure 31. Photo. Washington State Route 7 1 month after data collection.

Washington SR 7
Date: 7/17-7/18/2012
Period: Before

 

location (gps at center of curve)

2 Lane with 12" Rumble

NB 11' Lane; SB 10' Lane

# lanes and width

Right

curve direction (left or right)

Paved

shoulder type and width

50

posted speed of curve in each direction

50

tangent speed in each direction

20

advisory speed in each direction

See Below

grade (average of 3 readings and list if positive or negative)

See Below

super elevation

See Layout

location and type of signing before and in the

Asphalt, Good

pavement type and condition

None presence and location of street lighting

Figure 32. Chart. Washington State Route 7 site information.

 

Wisconsin 213
Date 5/21 - 5/22, 2012
Period: Before
Composite image: Wisconsin Highway 213 southbound before implementation, showing table data pointing to map for upstream, point of curvature, and center of curve
Figure 33. Map. Wisconsin Highway 213 before data collection.

 

Wisconsin 213
Date 5/21 - 5/22, 2012
Period: Before
Composite image: Wisconsin Highway 213 southbound 1 month after implementation, showing table data pointing to map for upstream, point of curvature, and center of curve
Figure 34. Map. Wisconsin Highway 213 1 month after data collection.

 

Wisconsin 213
Date 5/21 - 5/22, 2012
Period: Before
Map: Wisconsin Highway 213 site layout showing relative locations of curve warning with advisory speed, intersection sign, driveway, and left arrow sign approaching the curve
Figure 35. Map. Wisconsin Highway 213 site layout.

Wisconsin 213
Date: 5/21-5/22/2012
Period: Before

N42°35.977' W089°12.570'

location (gps at center of curve)

2 Lanes, 24'

# lanes and width

Left

curve direction (left or right)

3' Asphalt with varying gravel edge

shoulder type and width

55

posted speed of curve in each direction

55

tangent speed in each direction

50

advisory speed in each direction

Below

grade (average of 3 readings and list if positive or negative)

Below

super elevation

Previous Slide (5 Chevrons)

location and type of signing before and in the

Asphalt, Good

pavement type and condition

None

presence and location of street lighting

 

Grade

Begin W-E

Center W-E

End W-E

SB

Center

NB

Average

SB

Center

NB

Average

SB

Center

NB

Average

-4.9

-4.9

-4.8

-4.87

-5.6

-5.4

-5.7

-5.57

-3.8

-3.2

-3.1

-3.37

 

Super Elevation

Begin S-N

Center S-N

End S-N

SB

Center

NB

Average

SB

Center

NB

Average

SB

Center

NB

Average

-3.8

-3.5

-4.7

-4.00

-6.5

-7.1

-8.6

-7.40

-4.6

-4.8

-5.4

-4.93


Figure 36. Chart. Wisconsin Highway 213 site information.

 

Wisconsin 20
Date 5/21 - 5/22, 2012
Period: Before
Composite image: Wisconsin Highway 20 westbound before implementation, showing table data pointing to map for upstream, point of curvature, and center of curve
Figure 37. Map. Wisconsin Highway 20 before data collection.

 

Wisconsin 20
Date 7/9 - 7/10, 2012
Period: 1 Month After
Composite image: Wisconsin Highway 20 westbound 1 month after implementation, showing table data pointing to map for upstream, point of curvature, and center of curve
Figure 38. Map. Wisconsin Highway 20 1 month after data collection.

 

Wisconsin 20
Date 5/21 - 5/22, 2012
Period: Before
Map: Wisconsin Highway 20 site layout showing relative positions of heavy trucks pulling in and out, watch for backups with railroad below, curve warnings with advisory speeds, three-leg intersection sign, Honey Creek Road left sign, railroad crossing sign and pavement markings right before point of curvature, left turn sign between the third and fourth chevrons, and railroad crossing sign
Figure 39. Map. Wisconsin Highway 20 site layout.

 

Wisconsin 20
Date: 5/21-5/22/2012
Period: Before

N42o46.212' W088o18.078'

location (gps at center of curve)

2 Lanes, 25'

# lanes and width

Right

curve direction (left or right)

South (2' Asphalt, 6' gravel)

North(14' Asphalt w/Drainage

shoulder type and width

55

posted speed of curve in each direction

55

tangent speed in each direction

30

advisory speed in each direction

See Below

grade (average of 3 readings and list if positive or negative)

See Below

super elevation

See Layout (9 Chevrons)

location and type of signing before and in the curve

Asphalt, Good

pavement type and condition

None

presence and location of street lighting

 

Grade

Begin W-E

Center W-E

End S-N

SB

Center

NB

Average

SB

Center

NB

Average

SB

Center

NB

Average

3

3

2.5

2.83

7.3

7

7.2

7.17

-5.9

-6.4

-6.5

-6.27

 

Super Elevation

Begin S-N

Center S-N

End W-E

SB

Center

NB

Average

SB

Center

NB

Average

SB

Center

NB

Average

-4

-5.3

-3

-4.10

-7.7

-8.3

-8.2

-8.07

-3.4

-5.6

-4

-4.33

Figure 40. Chart. Wisconsin Highway 20 site information.

 

Wisconsin 67
Date 5/21 - 5/22, 2012
Period: Before
Composite image: Wisconsin Highway 67 before implementation, showing table data pointing to map for upstream, point of curvature, and center of curve
Figure 41. Map. Wisconsin Highway 67 before data collection.

 

Wisconsin 67
Date 7/9-7/10 2012
Period: 1 Month After
Composite image: Wisconsin Highway 67 1 month after implementation, showing table data pointing to map for upstream, point of curvature, and center of curve
Figure 42. Map. Wisconsin Highway 67 1 month after data collection.

 

Wisconsin 67
Date 5/21-5/22 2012
Period: Before
Map: Wisconsin Highway 67 site layout showing relative locations of passing lane northbound, three curve warnings with advisory speeds, and guardrail on south side through curve
Figure 43. Map Wisconsin Highway 67 site layout.

Wisconsin 67
Date: 5/21-5/22/2012
Period: Before

N42o56.244' W088o28.056'

location (gps at center of curve)

2 Lanes, 24'

# lanes and width

Right

curve direction (left or right)

South (3.5' asphalt w/4' Gravel

then guardrail through curve)

North (1.5' asphalt w/ 3' gravel)

shoulder type and width

55

posted speed of curve in each direction

55

tangent speed in each direction

25

advisory speed in each direction

See Below

grade (average of 3 readings and list if positive or negative)

See Below

super elevation

See Layout(5 Chevrons)

location and type of signing before and in the curve

Asphalt, good

pavement type and condition

None

presence and location of street lighting

 

Grade

Begin W-E

Center W-E

End S-N

SB

Center

NB

Average

SB

Center

NB

Average

SB

Center

NB

Average

-1.6

-1.7

-1.9

-1.73

-0.1

-0.12

-0.2

-0.14

0.7

0.6

1

0.77

 

Super Elevation

Begin S-N

Center S-N

End W-E

SB

Center

NB

Average

SB

Center

NB

Average

SB

Center

NB

Average

2

1.1

-0.4

0.90

5.8

5.2

5.1

5.37

3.6

3.2

3.1

3.30

Figure 44. Chart. Wisconsin Highway 67 site information.

Page last modified on July 17, 2013.
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000