Typical traffic paint and tape do not provide effective delineation during wet, nighttime conditions. Steel-casting snowplowable markers have been used by the Kentucky Transportation Cabinet (KYTC) since the 1980s to provide delineation under these conditions.
In recent years there have been increased maintenance issues related to the steel-casting snowplowable marker that has been used in Kentucky and many other states with significant snowfall. A recent evaluation of the use of snowplowable raised pavement markers concluded that the currently approved steel-casting marker could be used if it were properly installed on new pavements with a commitment to maintain the pavement and marker, but use of an alternative design should be evaluated.
A potential method of alleviating damage to pavement markings and to the pavement is to modify the current bare-pavement policy, which results in using the full weight of a steel snowplow blade on the surface. The goals of the KYTC snow- and ice-control program are to:
- Provide bare pavement or adequate traction on road surfaces;
- Keep traffic moving in a safe and uninterrupted manner;
- Provide statewide uniformity of pavement conditions within each snow- and ice-control-priority system; and
- Consider economic and environmental factors while achieving safe driving conditions.
Alternative procedures are used in other states to reduce the damage to pavement markings during snowplow operations. These include using alternative types of snowplow blades, procedures to reduce the weight of the plow on the pavement and plowing without the blade riding on the surface.
The objectives of this study were to investigate:
- Viable alternatives to the currently approved snowplowable raised pavement marker; and
- Alternative methods and equipment that could be used to plow roadways.
Completing the objectives of the study involved the following phases of work:
- Determine the state of practice related to the use of pavement markers in areas subject to snowplows;
- Determine the state of practice related to snowplowing procedures and equipment;
- Evaluate any potential durable and effective pavement marker that is not disruptive to snowplowing operations, and
- Evaluate alternative snowplowing procedures and equipment that do not damage pavement delineation and pavements.
Implementation possibilities resulting from the research project include:
- Identifying an alternative snowplowable marker; and
- Improved/alternative snowplowing procedures and equipment.
Coming up with an alternative
The first evaluation of snowplowable raised pavement markers (RPM) in Kentucky was conducted in 1982 and resulted in the recommendation that the steel-casting marker and a recessed-marker design should be used. Initial evaluation found they were effective with the recommendation that the steel-casting type of marker should continue to be used. Use of the snowplowable RPM continued in Kentucky for many years on a system of about 5,400 miles until issues with durability started to occur. There have been national questions concerning both the effectiveness of RPMs in reducing crashes and the durability of these markers. A recent study in Kentucky concluded that continued use of the currently approved snowplowable marker can be justified if the castings are properly installed on new pavements with a commitment that the pavement and castings will be maintained, but there should be an evaluation of alternative snowplowable marker designs.
The literature was reviewed to determine the status of alternative snowplowable marker designs. Specifications providing marker designs for other states were reviewed. Also, various manufacturers were contacted to determine the status of alternative designs. Specifications were located for a few states, which had various designs for recessed markers. The specifications are very similar as far as the dimensions of the cut. Also, observations were made of a large-scale installation of recessed markers.
A new design of a recessed marker was reviewed. The design (referred to as the Marker One pavement reflector) uses the same lenses typically attached to the traditional steel casting and places it in a long, shallow recessed groove. Two lenses are placed in a groove, which has a length of 8 to 9 ft. The depth of the groove goes down to 0.37 in. except for the area where the lenses are placed, which has a depth of 1 in. Different alignments of the two lenses have been used. The latest alignment uses a 9-ft groove with each lens placed 3.5 ft from the end of the groove.
Change in procedures?
Interviews were conducted with a representative from each of the 12 district offices of the KYTC with a person knowledgeable of the snowplowing procedure. The questions attempted to identify experience in the district and their opinion about possible changes, which could be used to improve the current procedure. Generally, the interviews revealed that considerable experience had been gained in snowplowing operations using steel blades, with limited use of any other alternatives unless bare-pavement results could be expected. It was acknowledged that use of steel blades occasionally resulted in removal of steel-casting markers, but only if the marker was loose or the pavement was deteriorating. Snowplowing is conducted by both the KYTC and contractors. A couple of contractors reported successful use of rubber blades.
KYTC contractor interviews
As a result of the district interviews where contractor experience was mentioned, two contractors who had used rubber blades also were identified. These contractors used rubber blades on interstates and offered the opinion that they were superior to steel blades in normal snow, with no difference on packed ice. Their rubber blades lasted four to six times longer than steel blades (40 to 46 hours compared with eight to 10 hours), by using metal wheels on the plow to prevent contact with the plow moldboard and the pavement.
Review of literature
The review of literature identified alternatives to the current snowplow procedure used in Kentucky, which involves a steel blade with full weight on the pavement. The following is a list of some of the alternative blades/procedures:
- Carbide blades;
- Rubber blades;
- Tungsten carbide inserted segments in rubber blade;
- Polyurethane blades;
- Polarflex blades;
- Plow weight-control systems; and
- Snowplow shoes.
Less than 1% missing
The Marker One recessed-marker design was determined to be the currently available alternative design to the traditional steel-casting snowplowable marker. The first large-scale tests have been part of resurfacing projects on four-lane rural roads. The first projects were installed in 2012 with a unit cost for these small contracts from $31.50 to $38. These grooves were 8 ft in length with two lenses in each groove (4 ft and 7 ft from the start of the groove). Other installations in 2013 placed the lenses 3 to 3.5 ft from the end of the groove with the length of the groove 8 to 9 ft.
The test sections were monitored during day and night conditions and during both dry and wet conditions. There was no water accumulation in the grooves where there was a grade. Water accumulation in the groove was observed around a hillcrest and on flat sections but infrequently were both lenses covered. The marker system remained effective during the rain. The benefit of having two lenses in each groove was demonstrated.
After one winter (with limited snowplow use) less than 1% of the approximately 1,850 lenses installed in 2012 were missing. No damage to the pavement has been noted as a result of the groove.
The review of the snowplow practice found alternative materials to the steel blade, and those blades were installed for use in one county (prior to the 2011-12 winter season). The blades were 12 ft in length. The rubber and ultra-high molecular polyethylene (UHMD) were 1.5 in. thick and 8 in. high.
The snowplow contractor placed blades on three of their trucks for use on a rural interstate. These blades were the JOMA 6000, rubber blade and rubber blade with UHMD backing. The Kuper blade was installed on a KYTC truck used on rural two-lane roads.
A form was developed to be completed by the snowplow operators after their use for each snowplow event. The following information was included on the form:
- The height of the blade before and after use;
- Miles plowed;
- Hours plowed;
- Type of event (snow or slush); and
- Comments (noise; vibration; effectiveness; pavement marker/bridge end issue).
There was a very limited use of the alternative blades during the 2011-12 winter season, with some use during the 2012-13 winter. The rubber blade sustained substantial wear in a few miles and was removed. The rubber blade with the UHMD backing and the JOMA blade performed as well as the steel blade with less vibration and bounce when the blade contacted the snowplowable markers.
The Kuper blade was removed after use in the 2012-13 winter season. There was wear on the blade, and the operator felt it had started to vibrate. An examination of the blade after removal indicated that the plow installation resulted in the edge of the blade contacting the pavement rather than the blade being flat with the pavement. This resulted in excessive wear.
The county obtained an additional rubber blade prior to the 2012-13 winter as part of a new plow obtained from the manufacturer. The rubber blade was used for about 50 miles during one snow event of about 5.5 hours. There was no excessive wear (with some wear on the back edge of the blade). The blade was quieter than the metal blade and was as effective. There was vibration with the rubber blade with no difference in bouncing of the blade when it hit an object in the road.
Another county used two rubber blades and one blade made of polyurethane material. One of the rubber blades was marketed as being made with a very abrasive-resistant rubber material. Both of the rubber blades are 10 ft long with a thickness of 1.5 in. The heights of the two blades are 8 and 10 in. The polyurethane blade had a 10-ft length with a height of 10 in. and a depth of 25?8 in. (with a cost of about $1,000). These blades were not used during the 2011-12 winter. One of the rubber blades was used during the 2012-13 winter. The rubber blade was used for slightly more than 20 miles and sustained substantial wear. An issue with the test section was that it included sections of high-friction surface, which may have increased wear.
Discussions were held with the contractor who reported successful use of rubber blades. The contractor noted the importance of attaching the rubber blade to the plow with one metal strip (rather than two). The rubber blades had been attached to the plow by two metal strips for the original KYTC tests. Future tests of the rubber blade should include attachment with one metal strip. Also, the contractor has used a wheel to indicate when the wear on the rubber blade has reached the plow.
Cities have used alternatives to the steel blade. Positive results were obtained with use of rubber blades at low speeds on city streets. They estimated that the rubber blades last a couple of years with flipping them after wear on one side.
Steel still solid
The alternative snowplowable markers included in the evaluation were the current steel-casting markers and the recessed marker: Marker One. The evaluations confirmed past research that showed the steel-casting marker can be used on new pavement if the casting and lenses are properly installed and maintained. Also, the pavement surrounding the casting must be maintained.
The limited experience with the recessed marker has shown it to be an effective alternative to the steel-casting marker. The durability and effectiveness of the recessed marker should continue to be monitored.
There are alternatives to the current snowplowing procedure of using steel blades with full weight on the pavement. Several types of blades were evaluated with varying levels of success. Evaluation of alternative snowplowing procedures should continue using information found from these initial tests. Contractors should be allowed the flexibility to use alternatives to steel blades with their performance monitored.
On a larger scale . . .
The initial evaluation of the recessed marker (Marker One) has found it has potential as an effective snowplowable marker. Installation of the recessed marker has been included in additional projects. Evaluation of these markers on a larger scale will allow a basis for a decision of their future use. Alternative designs for the placement of the two lenses in the groove will be evaluated.
Installation of the steel-casting marker will continue on multilane highways. The installation process will ensure that the markers are not installed on the pavement joint. Lenses must be replaced on an appropriate interval to maintain effectiveness, with the condition of the surrounding pavement evaluated.
Contractors will be allowed to use alternative snowplow blades. The effectiveness of alternative blades will continue to be evaluated as they are used on a larger scale. R&B