Tar Snakes: What Those Squiggly Black Lines on the Road Are (and Why Riders Hate Them)

Tar snakes are the shiny black lines you see winding across roads. They're not tar. They're strips of hot-poured crack sealant, usually a rubberized asphalt compound, that road crews apply over cracks to keep water out of the pavement. Sealing cracks is one of the cheapest ways to extend a road's life. The downside is that the sealant surface can be slicker than the surrounding asphalt, especially in hot weather or rain, which is why motorcyclists and cyclists watch out for them.

How crack sealing machines work →

Why Roads Get Tar Snakes

As asphalt ages, it cracks from temperature swings, oxidation and traffic. Water entering those cracks weakens the base and, in freezing climates, freeze-thaw action widens them further. Crack sealing is preventive maintenance: crews clean the crack, sometimes cut it wider with a router, and fill it with melted sealant. For how the equipment works, see our guide to crack sealing machines.

Why They're Wider Than the Crack

Many agencies use an "overband" or band-aid method: sealant is spread a couple of inches beyond each side of the crack with a squeegee or shoe. The overband helps the seal stick and bridges crack edges. It's also what creates the wide, glossy strip riders notice. Methods that keep sealant flush with the surface, or that leave only a narrow band, reduce the exposed area.

What They're Made Of

• Asphalt cement blended with polymers or ground rubber to stay flexible in cold and resist tracking in heat
• Fillers that add body
• Sometimes a light dusting of sand, fines or a detackifier after placement to reduce stickiness and improve grip

Our article on rubberized asphalt crack filler explains the homeowner versions of these products.

Why Tar Snakes Are Slippery

• Smooth surface: sealant lacks the stone texture of asphalt, so there's less for tires to key into.
• Heat: on hot days, the sealant softens and can feel greasy or tacky, and tires may slide slightly.
• Rain: water on a smooth surface can reduce traction, much like painted lines or metal plates.
• Fresh sealant: newly applied material may be softer before it weathers.

For most cars, the effect is minor. On two wheels, a small slide on a tar snake while leaning in a curve is more noticeable.

Riding Tips for Motorcyclists

• Scan ahead in curves and adjust your line to cross snakes at a more upright angle when possible.
• Avoid abrupt braking, throttle or steering changes while on the sealant.
• Stay loose on the bars; a small slide often corrects itself when you're relaxed.
• Reduce speed on roads with heavy sealing, especially on hot afternoons or in rain.
• Keep tires in good condition and at the right pressure.

Riding gear matters too. Quality protective motorcycle gloves and abrasion-resistant clothing are cheap insurance against pavement contact.

Tips for Cyclists

Narrow road-bike tires are more sensitive to smooth patches. Cross sealant strips upright and avoid leaning or braking hard on them in turns. In heat, sealant can stick to tires and pick up grit, so check tires after rides on freshly sealed roads.

Reporting Problem Sealant

If a stretch of road has excessive sealant, bleeding, or wide overbands on a curve, you can report it to the road owner, often the state DOT, county or town highway department. Include the location and photos. Agencies may add sand or apply surface treatments. In some places, tar-snake-heavy roads eventually receive a chip seal, microsurfacing or overlay that covers the sealant.

Tar Snakes on Your Driveway

Crack filler on a home driveway can leave smaller versions of the same thing. To keep it neat:

• Clean cracks with a wire crack-cleaning brush and blow them out.
• Fill slightly below the surface instead of heaping filler on top.
• Use a narrow squeegee or V-shaped tool to keep filler in the crack.
• Sprinkle a little sand on wet filler if it will be walked or driven on soon.

For choosing products, see our asphalt crack filler guide. A pourable rubberized crack filler works for many homeowner-size cracks.

Why Agencies Keep Using Crack Seal

Sealing cracks costs a fraction of patching or overlaying and can delay bigger repairs by years when done at the right stage. Pavement preservation programs rely on it heavily. The trade-off is surface appearance and some rider complaints, which agencies manage through application methods, material selection, and follow-up treatments.

Crack Seal vs Crack Fill

In industry terms, crack sealing typically targets working cracks (ones that open and close with temperature) and uses flexible, high-performance sealants, often after routing. Crack filling targets less active cracks and may use less expensive materials. Both can leave tar snakes.

When Tar Snakes Are a Sign of a Bigger Problem

A few sealed cracks are normal on an aging road. A dense web of sealant, especially in a pattern of interconnected blocks or alligator-style cracks, usually means the pavement is near the end of its life and sealing is only buying time. Alligator cracking often points to a weak base or heavy loads, and sealing alone won't fix it. At that point, the road owner is usually looking at patching, milling and overlaying, or reconstruction. If your private road or long driveway is covered in sealant, it may be time to price out a resurfacing instead of another round of crack filling.

Bottom Line on Tar Snakes

Tar snakes are crack sealant, applied to keep water out and make roads last longer. They can be slick in heat and rain, so riders should cross them upright, avoid sudden inputs, and slow down on heavily sealed curves. On driveways, fill cracks neatly to avoid wide, glossy bands.