Asphalt Paving and Sealcoat  Blog

Pavement Marking Lines pt.1

Edgelines
Pavement edgeline markings give drivers a guide to the
edge of the pavement and also enhance safety. A study
of rural highways in Kansas showed that edgelines will
yield benefits exceeding their costs if an average of one
non-intersection crash occurs annually every 15.5 miles
of roadway. Edgelines are a particularly valuable visual
reference during bad weather and poor visibility, especially
along curves. They can also be used to mark the
pavement edge to reduce driving on paved or unpaved
shoulders. Break edgelines for intersections, major
driveways or interchanges. Continue edgelines through
minor driveways unless a full width turn lane has been
provided. Wide solid edgeline markings may be used
for greater emphasis.

Required (shall)
• Rural arterials 20' or more in width and 6000 vehicles
per day or more.
• Freeways and expressways.

Recommended (should)
• Rural arterials and collectors 20' or more in width
and 3000 vehicles per day or more.

Optional (may)
• Other paved streets based on engineering study.

Channelizing lines
Channelizing lines can be used to form channelizing
islands where traffic is going in the same direction on
either side of the island. They shall be a wide or double
wide solid white line. White diagonals or chevron marking
can be placed between the channelizing lines for
greater emphasis.

Yield lines
Yield lines are white and shall
consist of a row of solid white
isosceles triangles pointing
toward approaching traffic.
They are not required, but
may be helpful at roundabouts,
mid-block crosswalks, or other
locations with yield signs.

Stop lines
Stop lines are solid white lines and should be 12"-24"
wide. Stop lines emphasize the stop condition and
indicate where to stop. They are not required, but are
helpful in many situations. For example, visibility may
be better at a point closer to the intersection than the
stop sign can be placed. The stop line can be used to
show this to drivers. Stop lines should be a minimum of
4' in advance of a marked crosswalk. Do not use stop
lines with yield signs. Place no closer than 4' from the
nearest edge of the intersecting travel way and no more
than 30'.

Pavement Markings General Principles

General principles
Pavement markings should conform to the following general principles:

Color
Pavement markings must be yellow or white. Red and
blue are used in special cases:
• Yellow longitudinal lines separate traffic flowing
in opposite directions, or mark the left edge of the
pavement on one-way roadways.
• White longitudinal lines separate traffic flowing in
the same direction, or mark the right edge of the
pavement.
• Contrasting black marking placed next to a white
marking may be used to make the white line stand
out on light-colored pavements.
• Words and symbols, crosswalk and stop lines are
white.
• Red and blue are used in special cases. Blue is for
parking spaces for persons with disabilities; red for
raised pavement markings for roadways that shall not
be entered such as one-way streets or alleys.

Width
• Line width indicates the degree of emphasis. Normal
centerlines and edgelines are 4"-6" wide. A wide line
is at least twice the width of a normal line.

Number
• Double lines-two normal width lines separated by
a discernible space-indicate maximum restriction:
driving across them is prohibited.

Solid vs. broken
• Solid lines discourage crossing and should not be
crossed. Broken lines may be crossed.
• A broken line is formed of segments and gaps, usually
in the ratio of 1:3. For example, on rural roads a 10'
segment would be followed by a 30' gap.
• Dotted lines provide guidance and are generally
used as line extensions. They have noticeably shorter
segments: for example, a 2' line and a 2' to 6' gap.
A dotted line where a lane is dropped or added may
consist of a 3' line and a 9' or 12' gap. The marking
shall be the same color and width as the line it
extends. A normal-width line may be used to extend
a wide line through an intersection.

Pavement Markings Materials

Many materials can be used for pavement marking. The choice depends on cost, durability, retroreflectivity, pavement surface, and drying time.

Paint Water-based paint, applied either cold or hot, is the most commonly used pavement marking. It is low cost with a short drying time, but its visibility on wet nights is just moderate. Traffic and snow plowing wear it away in about a year. Oil-based (alkyd) paint, when used, must meet environmental air quality restrictions
on volatile organic compound (VOC) emissions.

Thermoplastics These pavement-marking materials are made of thermoplastic heated to about 400° F and spread onto the pavement surface. Glass beads to increase reflections can be spread on top, mixed in, or both. Thermoplastics have a long service life, good visibility, and good retroreflectivity. The no-track time is short, and cost is mid-range. Special application equipment is required.

Epoxy Also applied as a liquid with special equipment, epoxy has good visibility and retroreflectivity, and cost is moderate. No-track time is 5-20 minutes. Markings last 3 to 4 years.

Tapes Pre-formed tape can be either inlaid as part of new construction, or overlaid. It has excellent visibility and retroreflectivity and lasts 7-8 years, but is higher cost. Wet reflective tape has excellent wet night retroreflectivity with about a 4-year life. Cost is medium and durability is poor. Modifications are being made to produce a tape with both durability and wet night
retroreflective quality.

Markings that must be visible at night shall be retroreflective. In general this applies to all pavement markings except parking lines and curb markings. For paint, glass beads are mixed in or dropped on the markings while still wet. Durable products are made with reflecting materials. In pedestrian areas, marking materials should not create slipping or tripping hazards.

Raised pavement markers can be useful to supplement pavement marking, but cost is a factor, and they must be correctly installed. Wet reflective tape is another supplement option.

Pavement Markings

Pavement markings have important functions in providing guidance and information to drivers. In some cases they supplement
regulations or warnings given by other devices. In other cases they are used alone and produce results that cannot be obtained by any other device.

Pavement markings can also enhance safety. Centerlines have been shown to cut crash frequency by 29% compared to roads
without them. Marking types include not only pavement and curb marking but also object markers, delineators, colored pavements,
barricades, channelizing devices, and islands.

Pavement markings have limitations. They are obliterated by snow, may not be clearly visible when wet, and may not be very durable under heavy traffic. It may be necessary to refresh them every year or more often. Despite these limitations, pavement markings are still used because of their unique advantage: they convey information to drivers without diverting their attention from the road.

 

Porous Asphalt - part 2

 

How long do these pavements last, and how long do they remain porous?

Even after twenty years, porous pavements show little if any cracking or pothole problems. The surface wears well. Porous asphalt retains its ability to handle rain water for many years. One of the best-known porous parking lots, located at the Walden Pond State Reservation in Massachusetts, was constructed in 1977. While it has never been repaved, it is in good shape and still drains effectively.

In a study of a porous pavement system constructed at the Centre County/Pennsylvania State Visitor center, researchers found that the system had maintained a consistent infiltration rate. During a 25-year precipitation event, there was no surface discharge from the stone beds.

Do these pavements look "different?" Are they smooth?

While slightly coarser than standard asphalt, porous asphalt pavements are attractive and acceptable. Most people parking on a porous asphalt parking lot will not notice (or believe) that it is porous. The surface of a porous asphalt pavement is smooth enough to meet requirements of the Americans with Disabilities Act (ADA).

What special additives or construction techniques are needed?

An added advantage to porous asphalt is that it does not necessitate proprietary ingredients. It does not require the contractor to have special paving equipment or skills. With the proper information, most asphalt plants can easily prepare the mix and general paving contractors can install it.

How does porous asphalt affect water quality?

There has been limited sampling data on the porous pavement systems, although the available data indicate a very high removal rate for total suspended solids, metals, and oil and grease.

Are there other environmental benefits?

Because of the open structure of the pavement, porous asphalt offers a "cooler" pavement choice. By replenishing water tables and aquifers rather than forcing rainfall into storm sewers, porous asphalt also helps to reduce demands on storm sewer systems. In areas where storm-water impact fees are imposed by local governments, such fees may be reduced by using porous asphalt.

 

Porous Asphalt - part 1

Porous asphalt pavements are of great interest to site planners and public-works departments. With the proper design
and installation, porous asphalt can provide cost-effective, attractive pavements with a life span of more than twenty
years, and at the same time provide storm-water management systems that promote infiltration, improve water quality,
and many times eliminate the need for a detention basin. The performance of porous asphalt pavements is similar to that
of other asphalt pavements. And, like other asphalt pavements, they can be designed for many situations.

How does it work?

The technology is really quite simple. The secret to success is to provide the water with a place to go, usually in the form
of an underlying, open-graded stone bed. As the water drains through the porous asphalt and into the stone bed, it slowly
infiltrates into the soil. The stone bed size and depth must be designed so that the water level never rises into the
asphalt. This stone bed, often 18 to 36 inches in depth, provides a tremendous subbase for the asphalt paving.

What does it cost?

Special features such as the underlying stone bed are more expensive than conventional construction, but these costs
are more than offset by the elimination of many elements of standard storm-water management systems. On those jobs
where unit costs have been compared, a porous asphalt pavement is generally the less-expensive option. The cost
advantage is even more dramatic when the value of land that might have been used for a detention basin or other stormwater
management features is considered.

CRACK TREATMENT: Clean and Seal

Pavement Surface Preparation for Prime Coat

A good prime coat requires a base course surface thatis smooth, properly crowned, and free from

wash boarding, ruts and standing water. This must bechecked immediately before the prime coat is applied.

On very tight, dense bases sweeping with a power broommay be needed to remove a dust seal that has built up under traffic. More oftenthe base is “tight bladed” with a motor grader. This slightly loosens thesurface, which helps the prime penetrate. It also removes any loose rock.

As with tack coats, the worst enemy of a prime coat isdry dust. The surface of the base course should be slightly damp (notwet) for the prime to penetrate properly. Dry dust can be eliminated with alight fog of water sprayed under high pressure from a water truck. Whether towater, and how much to water, is a decision which must be made by theinspector. This decision is based on how moist the grade is, how hot and sunnyit is and how soon it will be primed. Too little moisture and the prime willnot penetrate; too much and it will puddle up or even run off the grade.

Paving Alignment, Grade, and Compaction

Alignment is the horizontal positioning of the road orrunway; grade is the vertical positioning. The plans describe the alignment andgrade of a “profile line” for the road, lot, driveway, or taxiway. This is mostoften the centerline of the structure. The alignment and grade of other pointsrelative to the profile line is shown in one or more “typical sections” in theplans.

The alignment and grade must be checked and approvedby the grade inspector prior to priming. This ensures that the road or runwayis in the correct location. This sounds simple but stakes are lost duringconstruction and mistakes do occur.

The surface width of the road must also be checked;sometimes it is narrower than the planned paving width and must be corrected.The position and slope of the crown must be checked too (or just the slope in asuper elevated section).

Compaction of the base course must be checked andapproved prior to priming. The check is made by means of density testsperformed by materials inspectors.

Preparing an Aggregate Surface (Prime Coat)

Liquid asphalt materials with high penetrationqualities are used for prime coats. They are sprayed onto an aggregate surface,where they coat and bond the aggregate. Prime coats provide a temporarywaterproofing of the base course surface and a permanent bond between the basecourse and asphalt concrete pavement. Prime coats may also preserve thefinished base coarse for a few days if traffic must be allowed on it beforepaving begins, especially in wet weather. They also provide a zone oftransition in asphalt content between the pavement and the untreated materialbelow.

Occasionally priming is deleted from a paving project.This may be considered late in the season when air temperatures are too coldfor priming but still allows paving. Prime coats serve a real purpose in thepavement structure, however, so deletion is normally not allowed. Deletion of aprime coat must be approved at the Regional level.

Sometimes an asphalt treated base is usedinstead of a primed base. 

Tack coat bonds old pavement to new pavement

The Standard Specifications call for STE-1 EmulsifiedAsphalt to be used for tack coats. On some contracts the special provisions maycall for a heavy grade of cutback asphalt instead.

A distributor truck applies the tack. Proper operationof the distributor truck is the key to a good tack job.

Application rates vary and will be set forth in thecontract specify 0.04-0.10 gals/sq.yd.. The tack coat should give a uniformcoat without excess. The inspector may adjust the application rate if thecoverage is too heavy or too light. As a general rule, a small amount of theexisting pavement should show through the tack coat. Too much tack can causeslippage between old and new pavements or bleeding.

Care must be taken to prevent spray overlap or missedareas at longitudinal joints between shots of tack.

Missed spots can be tacked with the hand sprayer, butthe result will be better if the application is done right in the first place.

 

At transverse joints, building paper should be placedover the end of the old shot of tack and the new shot should begin on the paper.

The tack should be applied the same day the surface ispaved and must be in good condition when the paving machine reaches it. It isthe Contractor’s responsibility to protect the tacked surface from damage untilthe pavement is placed.

Tack should be allowed to break before paving begins.When it breaks it will change from chocolate brown to black and from gooey (itwill stick to your fingers) to tacky (it will feel sticky but will not stick toyour fingers). Paving before the tack breaks results in the equipment pickingthe tack up off the road, which defeats the benefit of the tack.

Weather limitations given in the contract should bestrictly adhered to. Rain can wash unbroken emulsion off the grade, ruining thetack and creating a serious pollution problem. It can cause a serious publicrelations problem with the traveling public, if this oil is splashed on theircars. And it can cause extremely hazardous driving conditions. Tacking is neverallowed in rainy weather. Tack is normally paid for by weight. Asphalt emulsion(STE-1) is diluted with an equal amount of water prior to application. CSS-1 ispaid for before it is diluted.

The distributor truck is weighed before and after theapplication and during the mixing process to determine the amount of tack thatwas placed.

Curbs, manholes, and other surfaces on which asphaltconcrete will be placed or abutted must be tacked by hand prior to paving.Surfaces of curbs, etc. that will not have pavement placed on them mustbe protected from over spray from the distributor.

Surface Preparation for Tack Coat

The Contractor must clean the old pavement if it is dirty or covered with debris. A power broom is normally used, but in extreme cases flushing with water may be necessary. The worst enemy of a tack coat is dry dust. A slightly damp (not wet) surface is preferable to a dry, dusty one. If all the dust cannot be removed, the old surface should be moistened slightly 0.05-0.10 gal/sq. yd. using a water truck with a high-pressure spray bar.

Curbs, manholes, inlets, and the like are usually dirty and require cleaning with a hand broom prior to the application of a tackcoat.

PAVEMENT SURFACE PREPARATION

Preparing Existing Pavement (Tack Coat)

Pavements deteriorate with time. Air, water, traffic and temperature cycles all shorten pavement life. Existing pavements are overlaid to correct surface irregularities, to strengthen the pavement structure and to seal out air and water.

Preparation for a pavement overlay includes cleaning dirt and debris off the old pavement and applying a tack coat. Tack is an asphalt product (usually an emulsion), which is sprayed on existing pavement in a thin film.

It provides a bond between old and new pavement.

If the old pavement has severe dips or ruts, it may require leveling with asphalt concrete prior to the overlay.

It may also be necessary to raise manhole covers, storm water inlets and similar objects.

Leveling

If a need for filling dips and ruts is anticipated, it will generally be indicated on the typical section in the plans for the project. Small holes and cracks are filled by hand with a shovel and a rake. Larger dips will require leveling with a motor grader (blade) or with a paving machine.

Normal procedure is for the inspector to stretch a string line across the dip to determine its depth and then mark the edges of dip with orange paint. Depth in the dip is marked in tenths of feet of asphalt fill required.

The Contractor then fills it to the depth and dimensions indicated. Deep dips must be filled in successive layers, starting at the deepest point and working radially outward. Each lift must be compacted separately with the rubber-tired roller.

All old pavement surfaces must be cleaned and tacked prior to leveling.