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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
This magazine is an archived publication and may contain dated technical, contact, and link information.
|Publication Number: Date: Summer 1993|
Issue No: Vol. 57 No. 1
Date: Summer 1993
Pavement markings save lives and reduce congestion. This article, based on a study funded by The American Glass Bead Manufacturers Association, presents a benefit-cost analysis of edgelines, centerlines, and lane lines. The analysis considers markings applied with fast-drying paint or thermoplastic, the most frequently used marking materials in the United States. A literature review and telephone survey suggested striping with fast-drying paint costs $.035 per linear foot ($.11 per meter) in rural areas and $.07/lin ft ($.23/m) in urban areas. Thermoplastic lines cost more than painted ones, but can have lower life-cycle costs; in areas where snowplowing is unnecessary, they have longer lives.
Published literature suggests that existing longitudinal pavement markings reduce crashes by 21 percent, and edgelines on rural two-lane highways reduce crashes by 8 percent. Applying these percentages to published aggregate crash costs by roadway type yields the safety benefits. The analysis assumes markings improve traffic flow during the 6 a.m. to 7 p.m. period on arterials, freeways, and Interstate highways, increasing average speeds by 2 mi/h (3.2 km/h).
On average, each $1 currently spent on pavement striping yields $60 in benefits. The benefit-cost ratio rises with traffic volume. The urban ratio is double the rural ratio. Sensitivity analysis shows the benefit-cost ratios are robust. Where striping reduces congestion, the travel time savings alone yield a positive benefit-cost ratio for striping. Most highways already have a full complement of lines. Rural two-lane highways, however, sometimes lack edgelines. Edgelines on these roads will yield benefits exceeding their costs if an average of one nonintersection crash occurs annually every 15.5 miles (25 km) of roadway.
Driving down a dark road on a misty night is never pleasant. The only comfort comes from centerlines and edgelines. These pavement markings, along with lane lines, are important driving aids. The driver's manual advises watching the edgeline when blinded by oncoming headlights. Lane lines organize vehicles into efficient lanes on multilane roads. Centerlines help oncoming vehicles to avoid collisions. Even in daylight, pavement markings make it possible for vehicles to travel more safely and quickly. They reduce congestion and raise roadway capacity.
This article probes the costs and benefits of roadway pavement markings. It restricts itself to edgelines, centerlines, and lane lines - the longitudinal lines that run parallel to traffic. It shows that existing markings on different classes of roads have benefit-cost ratios ranging from 21 to 103. Most roads already have a full complement of lines. Some rural two-lane highways, however, lack edgelines; a few even lack centerlines. Edgelines would be cost-effective on a mile of rural two-lane highway if one crash occurred outside the roadway every 15.5 years.
Longitudinal pavement markings typically are applied using a liquid marking medium or binder that is visible during the day. The medium binds glass breads that make the lines visible when headlights shine on them at night. The principle underlying night visibility is retroreflectivity. Retroreflection means light reflects off the binder-coated backs of the beads and is returned to its source. Because the beads are almost perfectly round, the retroreflected light is concentrated in a small angle of return, making the marking conspicuous.
Existing binders include fast-drying, high-solvent paint; latex paint; thermoplastic; epoxy; and polyester. Some markings also are applied using preformed tape. This article computes benefit-cost ratios for the marking media that historically captured the largest market shares: high-solvent paint and thermoplastic. Other media, especially latex paint, have gained market share recently.
Fast-drying, high-solvent paint has dominated the U.S. market for many years. It is inexpensive to buy and apply. Because it dries very quickly, a trailing vehicle moving at 10 to 15 mi/h (16-25 km/h) can prevent traffic from tracking the newly applied paint. High-solvent paint has two drawbacks: a short life, often as little as 6 to 12 months, and environmentally damaging solvent emissions during application.
The newer latex paints are water-borne rather than solvent-borne. Thus, they avoid emission problems. Most latex formulations dry more slowly than high-solvent paint; typically, application proceeds at 5 mi/h (8 km/h).
Thermoplastic has captured roughly one-eighth of the U.S. striping market. Although costly to buy and apply, it has a long life - 4 to 7 years. Thermoplastic lines are much thicker than painted lines, which makes them more vulnerable to snowplow damage. Contractors apply most of the thermoplastic in most States.
The benefit-cost ratio computed in this article equals the monetized benefits from pavement marking divided by the marking costs. Let B equal the benefits expected per year from pavement marking and C equal the annualized marking costs. Then the benefit-cost ratio is:
(1) BCR = B/C
The benefits include both increased safety and reduced travel time benefits.
The next section of this article discusses marking costs. Subsequent sections describe the safety benefits, the travel time benefits, and benefit-cost ratios by roadway class.
Pavement markings rarely require maintenance between reapplications. Their useful life can range from 6 months to 7 years depending on the marking medium, traffic volume, location (with lane lines and centerlines requiring more frequent replacement than edgelines), and snowplowing (with plowing to bare road causting rapid deterioration). The annualized application costs are:
(2) C = M + P + E + ADMIN,
where M = annualized materials costs, including binder, beads, and fuel.
P = annualized personnel costs, including wages, fringe benefits, and per diem when crews are absent from home overnight.
E = annualized costs of equipment and storage facilities.
ADMIN = annualized contract letting, monitoring, and other administrative costs.
The annualized costs include multiple applications where the useful life is less than 1 year. The annualization multipliers used were capital recovery factors computed using the formula in Economic Analysis for Highways.(1) The analysis used a discount rate (present value factor) of 4 percent. That rate is recommended for use in analyzing highway safety countermeasures with lives less than 5 years. Sensitivity analysis examined the benefit-cost ratio at a 10-percent discount rate.
This article drew data on making costs from a literature review and a telephone survey. Table 1 summarizes the cost estimates per application. The top panel in the table shows published estimates; the bottom panel shows estimates from our telephone survey. Typically, the installed cost of high-solvent paint is $.035/lin ft ($.11/m) of 4-in (101.6-mm) stripe in rural areas and $.07/lin ft ($.23/m) in urban areas (in 1991 dollars).
[TABULAR DATA OMITTED - TABLE 1]
Thermoplastic costs vary widely, ranging from $.15 to $.40/lin ft ($.49 to $1.31/m). The average is $.32/lin ft ($1.05/m). Reasons suggested by the telephone survey for the wide variation include:
Most published costs are State averages. They mask substantial variability. Costs are low in suburban and rural areas where day-long striping will not disrupt traffic significantly. Urban striping costs often are higher. Reasons suggested by the telephone survey for higher urban costs are:
Comparing costs between striping media requires caution. The costs for high-solvent paint in table 1 assume lines will retrace existing lines. Such restriping generally is done by State forces. Striping after repaving or chip sealing requires premarking to establish line locations. This costs perhaps $.005 to $.01/lin ft ($.016 to $.033/m). The paving contract geenerally includes premaking and striping. Since striping usually is subcontracted, contract costs include two tiers of administrative expenses and profits. Unlike painting contracts, thermoplastic contracts often are first-tier contracts.
[TABULAR DATA OMITTED - TABLE 2]
The contract paint and thermoplastic costs in table 1 exclude the costs of contract letting and monitoring. The Texas Department of Transportation (DOT) estimated these costs at 5 percent of the contract price. The North Carolina DOT, which inspects more extensively than most, estimated the costs at 7 percent.
The analysis uses the following marking costs and material lives:
The miles striped by roadway type and land use were computed using data on number of lanes by roadway mileage. Undivided highways require one edge or lane line per lane plus a centerline. For example, a four-lane highway requires two edgelines, two lane lines, and a centerline; a six-lane highway requires two additional lane lines. Each side of a divided highway requires one edge or lane line per lane plus an additional edgeline. Line mileage was computed using the following assumptions:
Divided Interstated highways with more than four lanes have an average of seven lanes in urban areas and six lanes in rural areas.
The first column of data in table 2 shows the line-miles by roadway functional class (excluding local streets, which rarely are wide enough or traveled heavily enough to stripe) and rural-urban land use. Rural roads, primarily major collectors, account for more than 75 percent of the line-miles.
[TABULAR DATA OMITTED]
The benefits of marking, B in equation, are the present value of the sum of the annual benefits. The benefits for a 1-mi road segment are:
(3) B = A * R * CS + V * T * (1/So - 1/S),
where A = crashes per year on the road segment.
R = fractional reduction in crashes expected due to marking.
CS = cost savings per crash prevented.
V = annual traffic volume on the road segment.
T = the value of one vehicle-hour of travel time.
[So] = average speed on the road segment before marking.
S = average speed on the road segment after marking.
* = multiplication sign.
Safety benefits - the crash cost savings were adapted from The Costs of Highways Crashes. They include medical, emergency services, workplace, legal property damage, travel delay, and administrative costs, as well as lost wages/household production, pain and suffering, and lost quality of life. The benefit values were derived using the method dictated by the Federal Highway Administration (FHWA) and the U.S. Office of Management and Budget for valuing life-saving benefits.[5,6]
The analysis by roadway functional class (e.g., rural Interstate, urban arterial) uses total crash costs by road type and land use from The Costs of Highway Crashes. Total crash costs equal ACS. The second data column in table 2 summarizes the costs. The cost savings equal these costs times R.
To analyze striping benefits for rural two-lane roads in more detail, the nonfatal injury benefits were tailored to the injury distribution for related crashes. These includes crashes with first harmful events outside the roadway, plus head-on crashes. The injury distribution was computed using 1984 National Accident Sampling System data.
The related crashes are costly. The average benefit per related crash prevented, including fatal crashes and property damage only (PDO) crashes, is $95,000 (in December 1990 dollars). The benefits are $3,079,000 per fatal crash prevented and $154,000 per injury crash prevented. By comparison, The Costs of Highway Crashes reports that the average benefits of crash prevention are $48,000 for a police-reported crash and $79,000 for a police-reported injury crash..
The safety benefits are for a 4-percent discount rate. For sensitivity analysis, benefits at 10 percent were taken from unpublished tables.
Table 3 compares the costs per injury by police-reported severity at 4-percent and 10-percent discount rates. The nonfatal injury costs with a 10-percent discount rate are higher - an apparent anomaly. This occurs for two reasons. First, the value placed on the sum of lifetime earnings and quality of life is computed independently of the discount rate, using the method prescribed by the Office of Management and Budget. The sum equals $2.5 million in December 1990 dollars. Although earnings losses are less at a higher discount rate, because the sum is a constant, the value placed on lost quality of life rises by an off-setting amount. Second, to value the lost quality of life resulting from nonfatal injury, the discount rate was applied to compute a value per life year for lost quality of life. At a 4-percent discount rate, the loss per year equals the total loss divided by 20.8; at 10 percent, it equals the total divided by 10.2. Since nonfatal injuries predominantly affect quality of life in the year of the injury, the much higher value for a year of lost quality of life yields a higher average injury cost, even though costs in future years have a lower present value at the higher discount rate.(4,6)
Table 3. - Costs of An Injury by Police-Reported Severity and Discount Rate
|Police-Reported Severity||Cost by Discount Rate|
|K - Fatal Injury||$2,392, 742||$2,360,330|
|A - Incapacitating Injury||169,506||190,069|
|B - Evident Injury||33,227||43,770|
|C - Possible Injury||17,029||27,757|
|O - Property Damage Only||1,734||1734|
Source: Miller et al. (4) and unpublished supporting materials (inflated to December 1990 dollars)
A literature review on the percentage of crashes prevented by longitudinal pavement markings revealed several studies that used treatment and control groups. It also revealed some studies without well-matched controls and values from some studies without proper bibliographic references. Table 4 summarizes all the percentages. Most studies supplemented existing centerlines with edgelines.
Table 4. - Percentage Reduction in Crashes Due to Long Lines
Edgelines United States (7)
Utah (22, 24)
United States (7)
Average effectiveness was computed all the studies and for several subjects. The subsets included:
The averages ranged from 20 to 21 percent. The average for sound studies examined was 21 percent. This article assumes that roads already are market, meaning the present crash levels are 21 percent less than the levels without marking. Expressed in terms of current crash rates, the percentage reduction in crashes attributable to striping is 100(*).21/(1-21) = 26.5 percent.
The best American effectiveness study is Cost-Effectiveness and Safety of Alternative Roadway Delineation Treatment for Rural Two-Lane Highways, which examines rural two-lane roads This 10-State study includes more than 500 sites. Each site either had a significant and adequately maintained, nonexperimental change in delineation 2 or 3 years prior to the study or an undelineated, matched control site. Data were obtained on crash experience for 2 to 3 years at each site (at least 2 years before and 2 after delineation for the site with delineation added. The study finds adding both edgelines and centerlines reduces crashes by 36 percent. Adding edgelines to an existing centerline yields an 8-percent reduction. These percentages were used in the more detailed analysis of making rural two-lane roads.
Using the percentage reduction in crashes to compute safety benefits should yield conservative estimates. Several of the published studies suggest the percentage of injuries and fatalities reduced is greater than the percentage of crashes reduced.
The benefit-cost ratios by roadway type include travel time saved because edgelines and centerlines let traffic go faster on busy roads. The analysis assumes:
The analysis uses travel time values of 60 percent of the wage rate for the driver and 45 percent for passengers. These values are recommended by by The Value of Time and Benefits of Time-Saving, which critically reviews the literature. They also are used in the FHWA's Highway Economics Requirements System model. The average vehicle has 0.7 passengers. Time of day and day of week do not unduly affect occupancy. Therefore, it is reasonable to use this occupancy for peak hour trips.
The value of travel time saved per vehicle is 91.5 percent (60 percent + 45 percent *.7) of the wage rate. The average nonsupervisory wage in 1990 was $9.66/h. Thus, a vehicle-hour of travel time (T in equation 3) is worth $8.84.
Table 5 shows the annual vehicle miles of travel (vmt) by roadway class (V in equation 3).
[TABULAR DATA OMITTED - TABLE 5 ]
Applying equation 3 to the data given above yields benefit-cost ratios by roadway type and land use. Table 5 show the benefit-cost ratios for high-solvent paint (as well as vmt).
Nationally, pavement striping has a benefit-cost ratio of 60. On average, each dollar spent on longitudinal pavement markings yields $60 in increased safety and reduced congestion benefits. It saves $3 in medical care costs. The benefit-cost ratio is highest on arterial roads. The urban ratio is more than double the rural ratio. Annual benefits average $19,226/line-mi ($11,940/km).
Sensitivity analysis showed that the benefit-cost ratios were robust. The ratios by land use were not greatly affected by choice of marking medium, changed assumptions, or introduction of additional cost considerations. Table 6 summarizes the ratios.
Varying the paint cost affects the benefit-cost ratios but does not change their order of magnitude. Assuming a uniform restriping frequency of 9 months lowers the rural benefit-cost ratio but raises the urban ratio. Wear and tear, especially in the winter, probably reduces nighttime marking effectiveness to 9 months except on lightly traveled minor rural collectors. Because the effectiveness studies involved annual restriping, the effectiveness estimates already should incorporate this temporal decline. Assuming that they do not would reduce the benefit-cost ratio by 15 percent.
Typically high-solvent paint releases 69 lb of volatile organic compounds (VOC's) per mile (19.5 kg/km) of solid 4-in (101.6-mm) stripe. VOC's oxidize, creating ozone that can cause respiratory distress for sensitive people. They also are suspected carcinogens. An Analysis of Selected Health Benefits from Reductions in Photochemical Oxidants in the Northeastern United States suggests valuing the short-term health effects of VOC's at $620/ton (562/Mg) (inflated to December 1990 dollars). For each restriping, the cost is $21/mi ($13/km) of solid stripe. This value is primarily for the Northeastern United States, but A.J. Krupnick suspects it is also a reasonable national average. The value does not consider the long-term cancer risk or any effect on plants and animals.
The environmental costs suggest latex paint would be more cost-effective than high-solvent paint if its applied cost was $.004 more per linear foot ($.013/m) or $1.30 more per gallon ($.34 more per liter). The better durability of some latex paints might justify an even greater cost. These conclusions apply only to latex paints with fast drying times.
In climates where thermoplastic markings are practical, their long life makes their life-cycle cost competitive with painted markings. They are especially competitive on high-volume urban roads. For ease of comparison, the ratios for thermoplastic were computed as if it could be used nationwide.
The benefit-cost ratios presented so far assumed all longitudinal pavement markings are single, solid lines. In reality, centerlines often are doubled, and they are dashed in passing zones. The industry rule of thumb is that a centerline on a two-lane road takes 1.3 times as much paint as a solid line. Conversely, lane lines are dashed. Typical lane lines are 10-ft (3.05-m) stripes separated by 30-ft (9.15-m) gaps in rural areas and 9-ft (2.75-m) stripes with 12-ft (3.66-m) gaps elsewhere. Applying these ratios to the estimated line-miles marked yields paint-miles. Costing with paint-miles raises the benefit-cost ratio slightly. Table 6 shows the revised ratios both excluding and including environmental damage.
The benefit-cost ratio of 59 with environmental damage and paint-miles may be more accurate than the ratio of 60 for the base case. Considerating these additional costs raises the urban benefit-cost ratio but lowers the rural ratio.
Another possible model refinement would assume that longitudinal pavement markings are as effective at preventing unreported crashes as preventing reported crashes. Applying the under-reporting estimates from The Cost of Highway Crashes yields substantially higher benefits. It raises the benefit-cost ratio for al roads to 76.
Omitting the travel time savings affects the benefit-cost ratios only for congested roads. On these roads, savings in travel time alone would justify longitudinal pavement markings. On major rural roads, the benefit-cost ratios for these markings range from 6.4 to 10.2. if only reduced congestion is considered. On major urban roads, they range from 8.0 to 18.3. Where pavement markings will ease congestion, they almost surely will be cost-beneficial.
Ignoring the extra cost of contract pavement markings at repaving would raise the benefit-cost ratio. Using a 10-percent discount rate would affect the benefit-cost ratio minimally.
The lowest benefit-cost ratios for longitudinal pavement markings are for edgelines on rural two-lane highways. This section examines the benefit-cost ratio for these lines in more detail. It again uses equations (1) through (3). The analysis is by average daily traffic (ADT) volume. It ignores any travel times savings.
Cost-Effectiveness and Safety of Alternative Roadway Delineation Treatments for Rural Two-Lane Highways finds edgelines prevent 0.72 crashes per million vehicle-miles (0.45 per million vehicle-km) of travel on rural two-lane roads. Multiplying this value times the ratio of fatal crash rates per million vehicle-miles of travel on rural Federal-aid secondary roads in 1978 and 1988 suggests 0.48 crashes would be prevented today. This estimate is conservative, since nonfatal injury rates probably fell less than fatality rates. The low quality of the nonfatal injury data precludes their use in adjusting to present crash rates.
Figure 1 shows the benefit-cost ratios. Even at 500 ADT, edgelines on rural two-lane roads yield $17 in safety benefits for every dollar invested.
Edgelines reduce crashes by 7.9 percent on rural two-lane roads with lane widths of 11 ft (3.36 m) of more. Using the estimate, the number of crashes per year needed to justify striping (A) can be computed as:
(4) A = C/ (CS * R)
= 2 edgelines * 240 /mi/ ($95,074/crash * .079)
Edgelines are justified on a rural two-lane highway with .064 or more crashes/mi/yr (.04/km/yr). Interpreting this number conservatively, edgelines are justified if an average of one nonintersection crash occurs annually every 15.5 mi (25 km). However, edgelines are not recommended if lane widths are less than 11 ft (3.36 m).
Existing longitudinal pavement markings yield benefits far greater than their costs. They increase safety and reduce congestion. Much of the safety benefit is achieved during periods of poor visibility. That suggests checking roadway retroreflectivity regularly and restriping promptly when retroreflectivity drops below recommended levels.
Edgelines may not be used often enough on rural two-lane roads in some States. The number to nonintersection crashes needed to justify edgelines is quite small. Rural collectors have far higher crash costs per million vehicle-miles of travel than other roads. Wider use of edgelines on these roads may be a cost-effective way to cut the crash toll.
The American Glass Bead Manufacturers Association funded this study. Study liaison Dave Mastro of Potters Industries provided many helpful insights. Thanks to the many government agencies and ASHTO affi hates that provided data on striping costs and useful lives.