U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
| REPORT |
| This report is an archived publication and may contain dated technical, contact, and link information |
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| Publication Number: FHWA-HRT-16-035 Date: June 2016 |
Publication Number: FHWA-HRT-16-035 Date: June 2016 |
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.
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 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.
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:
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.
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.
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.
| 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 |
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 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.
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:
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.
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.
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.
| 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 |
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 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.
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:
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.
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.
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.
| 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 |
Table 9 defines the crash types used by each State. The project team attempted to make the crash type definitions consistent.
| 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.
| 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.
| 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.
