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Publication Number:  FHWA-HRT-16-035    Date:  June 2016
Publication Number: FHWA-HRT-16-035
Date: June 2016

 

Safety Evaluation of Intersection Conflict Warning Systems

Chapter 5. Data Collection

Minnesota, Missouri, and North Carolina provided data containing locations and dates of ICWS installations. Each State also identified approximately 30 reference sites for four-legged intersections with two lanes on the major route and 30 reference sites for four-legged intersections with four lanes on the major route. These States also provided roadway geometry, traffic volumes, and crash data for both installation and reference sites. Additional details about the design, installation, and maintenance of ICWSs, as well as lessons learned, can be found in appendix B.

Minnesota

Installation Data

The Minnesota Department of Transportation (MnDOT) provided a list of intersections where ICWSs had been installed, along with information about whether the installations were on the major and/or minor routes. In addition, the list provided by MnDOT included information about the specific messages shown on each of the signs or whether the ICWS consisted of a visual display. The final list of installation sites comprised 10 two-lane at two-lane intersections and 3four-lane at two-lane intersections (13 total installation sites). All Minnesota installation sites were post mounted, and all sites had a warning sign on the minor roadway approach. Six of the two-lane at two-lane intersections also had an installation on the major approaches of the intersections. The four-lane at two-lane intersections had visual displays for minor route approaches. All two-lane at two-lane installations specified “WHEN FLASHING” on the messages provided on the warning signs. Twenty more installation sites were identified by MnDOT, but these were still in the process of being installed and thus could not be used in this study.

Reference Sites

Reference sites were provided by MnDOT separately for two-lane at two-lane intersections and for four-lane at two-lane intersections. Data were provided for 28 two-lane at two-lane intersections and 35 four-lane at two-lane intersections. Intersections were identified that were in close proximity to the installation sites, preferably along the same major route as installation sites. Sites were selected if they had similar traffic and geometric characteristics to installation sites. Selecting sites in close proximity reduced the effects of differences in driver population and spatial factors, such as weather or terrain.

Roadway Data

MnDOT provided roadway data for the installation and reference sites. Various roadway characteristics were coded by the project team from the records provided, and from Google Earth™, including the following:

Traffic Data

MnDOT also provided traffic volume data for the installation and reference sites. Traffic data were typically available for State highways every 2 to 3 years. County highway data were provided for every 4 to 5 years. The years of average annual daily traffic (AADT) counts were provided for each value of AADT. The counts covered both the before and after periods for installation and reference sites. For years with missing data, linear interpolation of AADT counts were used, or an extrapolation was used if the after period counts did not cover the latest year. If no apparent trend was observed in the AADT data, the extrapolated value was defined as the same as the previous year’s AADT value.

Crash Data

MnDOT provided crash data for installation and reference intersections from 2006 to 2012. Because crash data were provided separately for each intersection, no linking was necessary, but the data had to be manually coded for each intersection.

ICWS Cost Data

MnDOT provided cost estimates of the installations for use in conducting a B/C analysis of the ICWS strategy. Table 6 provides itemized cost data for post-mounted signs for two-lane at twolane intersections and four-lane at two-lane intersections. The project team noted that intersection warning systems included static signs on the major road, blank-out signs on the minor road, micro-loops on the major road, loops or micro-loops on the minor road, controller cabinets, and onsite contractor warranty, which included a 72-h response to address any system malfunction. Maintenance and operations costs were not provided, nor was an estimate of lifespan.

Table 6. Minnesota installation cost data.
Countermeasure Mobilization Engineering Construction Design Build Oversight
Post-mounted on all approaches for two-lane major approach
~ $5,000
$11,807
$75,650
$17,000
Post-mounted on all approaches for four-lane major approach
~ $5,000
$13,130
$103,833
$17,000

Missouri

Installation Data

MoDOT provided a list of projects where ICWSs had been installed, along with information about whether the installations were on the major and/or minor routes. In addition, MoDOT provided details on how the ICWS signs were activated, the mounting type, the specific message on each sign, any additional signs/countermeasures, and any additional improvements made at the site during the analysis years. The final list of sites consisted of 6 two-lane at two-lane intersections and 8 four-lane at two-lane intersections (14 total installation sites). All Missouri installation sites were post mounted. Five of the six two-lane at two-lane intersections had ICWSs on the minor approaches. Two of the six had ICWSs on the major approaches. Five of eight four-lane at two-lane intersections had an ICWS on the minor approaches, and four had an ICWS on the major approaches. Two-lane at two-lane sites with an ICWS on the minor approaches had “WHEN FLASHING” plaques, while only one four-lane at two-lane site had the plaque.

Reference Sites

Reference sites were provided by MoDOT separately for two-lane at two-lane intersections and for four-lane at two-lane intersections. Data were provided for 35 two-lane at two-lane intersections and 28 four-lane at two-lane intersections. Intersections were identified that were in close proximity to the installation sites, preferably along the same major route. Sites were selected if they had similar traffic and geometric characteristics to installation sites. Selecting sites in close proximity reduced the effects of differences in driver population and spatial factors, such as weather or terrain.

Roadway Data

MoDOT provided roadway data for the installation and reference sites. Various roadway characteristics were coded by the project team from the records provided, and from Google Earth™, including the following:

Traffic Data

MoDOT also provided traffic volume data for the installation and reference sites. Traffic data were typically available for State highways every 2 to 3 years. County highway data were provided for every 4 to 5 years. The years of AADT counts were provided for each value of AADT. The counts covered both the before and after periods for installation and reference sites. For years with missing data, linear interpolation of AADT counts were used, or an extrapolation was used if the after period counts did not cover the latest year. If no apparent trend was observed in the AADT data, the extrapolated value was defined as the same as the previous year’s AADT value.

Crash Data

MoDOT provided crash data for the installation and reference intersections from 2000 to 2012. The crash data were linked to each intersection using the intersection identifier.

ICWS Cost Data

MoDOT provided estimates of the costs and services lives of the installations for use in conducting a B/C analysis of the ICWS strategy. Table 7 provides the approximate cost and lifespan for a post-mounted ICWS on the major approaches as reported by MoDOT. In addition, maintenance costs were noted to vary substantially. Annual maintenance costs for mainline warning systems with loops on the minor routes were estimated to be $800 per year. For intersections with mainline detection using probes or microwave and wireless communication, the estimated annual maintenance was $3,000 per intersection. Ignoring the cost of intersection lighting, utility costs were estimated to average $275 for mainline flashers and $400 for side-street flashers.

Table 7. Missouri installation cost and service life data.
Intersection Type Installation Type Cost Lifespan
Two-lane at two-lane intersection Post-mounted ICWS on major approach
$25,000 to $33,500
10 years minimum
Four-lane at two-lane intersection Post-mounted ICWS on minor approaches
~ $75,000
10 years minimum

North Carolina

Installation Data

NCDOT provided a list of intersections where an ICWS had been installed, along with information about whether the installations were on the major and/or minor routes. In addition, the list provided by NCDOT included information about the specific messages shown on each of the signs, the project improvement description, statement of existing physical conditions, statement of problem, additional countermeasures, sign size details, detector types, detector locations, and detector timings. The final list of installation sites consisted of 53 two-lane at two-lane intersections and 13 four-lane at two-lane intersections (66 total installation sites). All four-lane at two-lane installations were on major approaches, and nine had post-mounted ICWS signs. Four of the sites had overhead ICWS signs, and nine sites specifically stated “WHEN FLASHING.” Thirty-eight two-lane at two-lane sites had ICWS signs on the major approaches, and 23 had ICWS signs on the minor approaches. Post-mounted ICWS signs were present at 16 two-lane at two-lane sites, and 40 had overhead ICWS signs.

Reference Sites

Reference sites were provided by NCDOT separately for two-lane at two-lane intersections and for four-lane at two-lane intersections. Data were provided for 35 two-lane at two-lane intersections and 35 four-lane at two-lane intersections. These intersections were provided based on reference sites NCDOT had obtained for other projects, and all were used in this study.

Roadway Data

NCDOT provided roadway data for the installation and reference sites. Various roadway characteristics were coded by the project team from the records provided, and from Google Earth™, including the following:

Traffic Data

NCDOT also provided traffic volume data for the installation and reference sites. Traffic data were available for State highways every 2 years. Because NCDOT is responsible for State and county roads, all roads are considered to be State maintained. The years of AADT counts were provided for each value of AADT. The counts covered both the before and after periods for installation and reference sites. For years with missing data, linear interpolation of AADT counts was used, or an extrapolation was used if the after period counts did not cover the latest year. If no apparent trend was observed in the AADT data, the extrapolated value was defined as the same as the previous year’s AADT value.

Crash Data

NCDOT provided crash data for the installation and reference intersections from 1992 to 2012. The crash data were linked to each intersection using the intersection ID. All data were used for SPF development; however, a maximum of 5 years before and after were used for the analysis of installation sites.

ICWS Cost Data

NCDOT provided estimates of the costs and services lives of the installation for use in conducting a B/C analysis of the ICWS strategy. Total cost estimates were provided for each of the installations from 1996 to 2011. Owing to the difference in time for cost estimates, the cost estimates were normalized by consumer price index to develop an average cost based on 2014. Table 8 provides installation cost data for sites based on the type of ICWS and based on which approaches were installed. In addition, Table 8 contains information for annual maintenance cost, annual operations cost, and estimated lifespan for installations used by NCDOT for economic analysis.

North Carolina assumed an annual maintenance cost of $500 per year, an operations cost of $125per year, and a lifespan of 10 years for installations. These values did not differ by installation type. The average installation cost of an overhead sign on a single approach was approximately $30,000, with a maximum value of approximately $50,000. The average installation cost of a post-mounted installation on the major approach only was approximately $20,000 for two-lane at two-lane intersections, with a maximum value of approximately $50,000. For four-lane at two-lane intersections, the average cost was $117,000, and the maximum cost was $142,500. For two-lane at two-lane intersections with overhead signs on all approaches, the average cost was approximately $50,000, and the maximum cost was $78,000.

Table 8. North Carolina installation cost and service life data.
Condition Installation Cost Annual Costs Lifespan (years)
Minimum Mean Maximum Maintenance Cost Operations Cost
Overhead on minor only
$20,000 $29,500 $46,000 $500 $125 10
Overhead on major and minor
$20,000 $49,000 $78,000 $500 $125 10
Overhead on major only
$13,500 $28,000 $49,000 $500 $125 10
Post-mounted only two lane
$9,000 $21,600 $49,000 $500 $125 10
Post-mounted only four lane
$49,000 $117,000 $142,500 $500 $125 10

Data Characteristics and Summary

Table 9 defines the crash types used by each State. The project team attempted to make the crash type definitions consistent.

Table 9. Definitions of crash types.
Crash Type State
Minnesota Missouri North Carolina
Total Identified as all crashes, without exclusion Identified as all crashes, without exclusion Identified as all crashes, without exclusion
Fatal and injury Resulted in a fatality, or A, B, or C injury Resulted in fatal, disabling injury, or minor injury Resulted in K, A, B, or C severity
Right-angle Diagram is coded as 5—Right-angle Accident class name is coded as right-angle First harmful event is angle
Rear-end Diagram is coded as 1—Rear-end Accident class name is coded as rear-end First harmful event is rear-end
Nighttime Lighting condition is coded as sunrise, sunset, or any value of dark Lighting condition is coded as any value of dark Lighting condition is coded as dusk, dawn, or any value of dark

Table 10 summarizes information for the data collected for the installation sites. The information in table 10 should not be used to make simple before–after comparisons of crashes per site-year because it does not account for factors, other than the ICWS strategy, that may cause a change in safety between the before and after periods. Such comparisons are properly done with the EB analysis as presented later. Table 11 summarizes information for the reference site data.

Table 10. Data summary for installation sites.
Variable Two-Lane Sites Four-Lane Sites
Minnesota Missouri North Carolina Minnesota Missouri North Carolina
Number of sites
10 6 53 3 8 13
Site-years before
43 44 263 14 52 60
Site-years after
16 28 211 4 41 55
Total crashes before1
1.54 1.93 3.82 5.93 3.71 4.32
Total crashes after1
1.25 1.32 2.91 4.00 2.90 4.55
Fatal and injury crashes before1
0.74 0.89 2.23 3.79 1.96 2.87
Fatal and injury crashes after1
0.38 0.64 1.60 2.25 1.15 2.84
Right-angle crashes before1
0.70 1.09 2.43 3.57 2.08 3.15
Right-angle crashes after1
0.81 0.71 1.83 2.25 1.49 3.31
Rear-end crashes before1
0.21 0.16 0.30 0.50 0.52 0.22
Rear-end crashes after1
0.00 0.14 0.18 0.25 0.39 0.29
Nighttime crashes before1
0.21 0.30 0.49 1.07 0.89 0.58
Nighttime crashes after1
0.19 0.11 0.52 0.50 0.68 0.42
Major AADT before
Avg 2,374
Min 810
Max 6,300
Avg 2,547
Min 1,420
Max 4,846
Avg 4,076
Min 299
Max 11,450
Avg 11,293
Min 6,400
Max 17,800
Avg 14,773
Min 9,104
Max 37,504
Avg 9,193
Min 1,323
Max 27,635
Major AADT after
Avg 2,345
Min 900
Max 6,500
Avg 2,334
Min 973
Max 5,123
Avg 4,041
Min 830
Max 10,000
Avg 13,225
Min 7,300
Max 18,600
Avg 16,530
Min 9,285
Max 33,685
Avg 10,868
Min 1,934
Max 30,500
Minor AADT before
Avg 1,257
Min 600
Max 3,250
Avg 618
Min 196
Max 1,846
Avg 1,776
Min 420
Max 4,100
Avg 1,934
Min 1,200
Max 3,350
Avg 957
Min 269
Max 3,000
Avg 2,044
Min 568
Max 5,500
Minor AADT after
Avg 1,512
Min 550
Max 3,700
Avg 723
Min 243
Max 1,431
Avg 1,906
Min 370
Max 4,300
Avg 1,700
Min 1,250
Max 2,950
Avg 965
Min 404
Max 2,742
Avg 2,268
Min 890
Max 5,700

1Crash rates are presented as crashes/site/year.
Avg = Average.
Min = Minimum.
Max = Maximum.

Table 11. Data summary for reference sites.
Variable Two-Lane Sites Multilane Sites
Minnesota Missouri North Carolina Minnesota Missouri North Carolina
Number of sites
28 35 35 35 28 35
Site-years
196 455 672 245 364 630
Total crashes1
1.34 0.90 1.36 1.49 2.35 1.91
Fatal and injury crashes1
0.67 0.33 0.71 0.70 0.96 1.02
Right-angle crashes1
0.62 0.35 0.53 0.76 1.02 0.88
Rear-end crashes1
0.26 0.20 0.31 0.18 0.31 0.32
Nighttime crashes1
0.41 0.17 0.26 0.35 0.54 0.42
Major AADT
Avg 6,286
Min 2,033
Max 12,200
Avg 2,432
Min 79
Max 6,895
Avg 5,462
Min 720
Max 17,000
Avg 10,119
Min 3,250
Max 21,000
Avg 6,687
Min 3,169
Max 12,770
Avg 12,111
Min 3,541
Max 28,000
Minor AADT
Avg 1,462
Min 390
Max 4,400
Avg 330
Min 18
Max 1,176
Avg 1,095
Min 235
Max 5,300
Avg 1,337
Min 310
Max 4,400
Avg 493
Min 106
Max 1,455
Avg 1,049
Min 100
Max 5,600

1Crash rates are presented as crashes/site/year.
Avg = Average.
Min = Minimum.
Max = Maximum.

 

 

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