Pavement markings 101
Pavement markings are an important facet of road safety; they can communicate rules and warnings, often supplementing signage to provide additional visibility and clarity. The “Pavement Markings 101” session at the 2021 City Engineers Association of Minnesota (CEAM) annual conference reviewed the importance of pavement markings and explored different options for selecting, applying, and maintaining them.
Purposes and challenges
Senior Associate Jon Jackels from SRF Consulting Group started the 101 presentation with an overview of the different purposes and challenges of pavement markings.
According to the current edition of the Minnesota Manual on Uniform Traffic Control Devices (MN MUTCD), the main functions of pavement markings are to provide guidance and information to drivers. Regulatory markings such as yellow curbs and “no passing” double-lane lines can lay out rules and restrictions, Jackels said, and facility-use markings such as pedestrian crossing lines can indicate who is allowed to use what part of the road.
The MN MUTCD establishes a uniform system of traffic control devices for streets and highways in Minnesota and is a good overall guide for determining rules and requirements for pavement marking application. The current edition from MnDOT can be found at dot.state.mn.us/trafficeng/publ/mutcd.
“It’s a good reference to go back to and look at when you’re doing design,” Jackels said.
Further considerations have to be taken when applying the markings. Visibility, cost, longevity, maintenance needs, and ease of application are all factors that have to be considered, and there are often tradeoffs between different methods.
Retroreflective glass beads can increase nighttime visibility when dropped onto painted lines, for example, but they are easily scraped off by snowplows. Recessing them into grooves solves this problem but in turn creates issues with rain pooling in the grooves and muting the retroreflective properties of the beads. There’s been work to solve this problem by altering the retroreflective properties of the glass beads so that light can be returned to drivers even through water, Jackels said.
“Deciding on what materials to use for pavement markings requires consideration of many factors,” he said, “including type of pavement, preventive maintenance plans, need for wet weather visibility, type and speed of traffic, and ability to maintain markings.”
Colored lanes
Adrian Potter, principal at SRF, delved deeper into one very specific type of pavement marking: colored lanes.
Generally, Potter said, colored lanes are utilized to set aside space for a type of road user—most commonly bicycles and buses. This can take the form of an entire colored lane (usually green or red) or something more limited such as colored “bike boxes,” which set aside a spot at the head of an intersection where bicyclists can safely queue for the light.
“These have been used by many cities and are becoming more common,” Potter said. “These aren’t new things, but they seem to be growing in their use.”
When applying colored lanes, many of the points from Jackels’ general overview of pavement markings come into play—visibility, cost, longevity, maintenance needs, and ease of application must all be considered. Though the MN MUTCD has yet to standardize the rules for colored lanes, Potter recommended adopting consistent practices to minimize confusion and referring to the National Association of City Transportation Officials (NACTO) Urban Bikeway Design Guide and Transit Street Design Guide for more information (nacto.org/publications /design-guides).
| PAINT TYPE | LIFESPAN | COST PER SQUARE FOOT |
|---|---|---|
| Paint | 6 months to 2 years | $1.20 to $1.60 |
| Epoxy | 3 to 5 years | $8.00 to $11.00 |
| MMA (Methyl Methacrylate) | 3 to 6 years | $8.00 to $15.00 |
| Thermoplastic | 2 to 6 years | $10.00 to $14.00 |
| Colored Pavement | About as long as the original, structural pavement | Up to 50 percent more than noncolored, structural pavement |
Potter then described some potential materials and some of their pros and cons:
- Paint: Easy to apply since most cities already have painting equipment for their roads. Has low durability in high-traffic areas and can be slick when wet (can be solved by adding sand).
- Epoxy: Long-lasting and naturally both skid-resistant and retroreflective. Involves more specialized installation.
- MMA (methyl methacrylate): Quick to dry and durable. Less widely available, requires special equipment, and can be damaged by pooling water.
- Thermoplastic: Durable in high-traffic areas and easy to spot-treat. Cost-prohibitive over large areas.
- Colored pavement: Embedded treatment. Can be cost-effective if designers plan to install it at the same time as other renovations, but cost-prohibitive if there are not already plans to repave. Spot maintenance can be difficult.
“There is probably no one-size-fits-all answer here for what you would use for your bike lane or your bus lane,” Potter concluded.
—Sophie Koch, LTAP freelancer
Learn more:
- MnDOT Traffic Engineering Manual
- MnDOT Pavement Marking Field Handbook
- MnDOT Typical Detail Sheets
- MnDOT Approved/Qualified Products
- LRRB Tool for Prioritizing Pavement Markings
The CEAM ‘101 Series’
The “101 Series” made its first appearance during the 2020 CEAM conference. It was developed as a way of focusing on the foundational skills of municipal engineering—technical, political, ethical, etc.— and was primarily aimed at people who are new to the career path. The first year of the series included presentations on city functions, state aid, and traffic signals. The series was well-received during its pilot year and brought back for the 2021 conference with Engineering 101, Project Management 101, and Pavement Markings 101.