Motorcycle riders must pay attention to the road surface. Many hazards that go unnoticed in a car will crash a motorbike. This section lists some of the more common hazards I've encountered.
Crosswalks and other painted lines - These can be *extremely* slick when wet. Even when dry, painted lines often have less traction than normal asphalt.
Railway tracks - These can catch your front wheel and dump your bike. Pay attention to the angle tracks cross the road. Use as much of the road as necessary to get a safe attack angle. Be aware that occasionally tracks cross roads at *very* shallow angles and it only takes one in a hundred to create an unhappy statistic.
Railway crossing areas - Some of these have metal or wood instead of asphalt between the two tracks. When wet it can be very slick. If this is combined with a turn you'll be in for a nasty surprise.
Metal bridge decks - These will cause the bike to track with an uncomfortable weave. This isn't a problem but if the rider over reacts it can become one. So relax and let the bike track the metal groves. You'll be fine. The same goes for grooved pavement and sections of gravel road - the bike will handle fine if you let it.
Cattle guards - These usually have small metal strips running across the cattle guard. The strips are there for a smooth ride when crossing with a car. The strips are located roughly where you'd expect car tires to cross the cattle guard. Just line your bike up with one of the strips and ride over for a smooth ride! It doesn't have to be perfect, sometimes I miss the strip a little but it still works (presumably due to the width of the tires).
Oil, anti-freeze, grease - All these can be deadly in a corner. You'll go down before you can react.
Rain after a long dry spell - This can turn the roads into a skating rink. Let the rain wash the roads clear before you ride them. A half hour can make a huge difference.
Gravel on pavement - This can be deadly. Gravel is more common as the road becomes twistier. It seems cars have a hard time staying on the pavement when there are corners. Gravel problems tend to be worse in spring due to winter rains. A little bit of gravel should be avoidable (or you are riding too fast). Unavoidable gravel covering the entire corner can be taken in stride if there is plenty of asphalt showing and you are prepared to let the bike slide around a bit. The key is to relax, don't over-react and keep steering towards the exit line. Bikes are surprisingly stable and will usually ride it out. The real problem is a heavy gravel patch in a corner. Surviving that is mainly luck given you were already going too fast to stop or go around it...my best advice is to treat it like light gravel and hope the bike rides it out. If the back-end washes out, steer like a dirt bike and hope the rear tire doesn't suddenly get traction!!
Having said all that, most "gravel crashes" were unnecessary. Usually the rider is lacking in fundamental skills. Common physical errors are not looking far enough into a corner so not picking up the gravel soon enough, not being able to brake at the bike's capabilities, not being able to turn at the bike's capabilities and over-reacting when hitting the gravel (a one inch slide feels like a mile so people panic). Common mental errors are missing signs of probable gravel (tight corners, earlier history, gravel shoulders or embankments, hills that might have been washed out etc) and riding without regard for suitable error margins.
Leaves - They look innocent but are worse than gravel. Especially if wet.
Small animals - Hitting a mouse a 220km/h can put you in the ditch.
Especially on a light sport bike. Hitting a deer at 30 km/h can put you in the hospital on any bike. Be alert to wildlife hazards!
Standing water - Don't just charge through water like you would in a car. Depending on tires you can hydroplane which will make the bike feel like it's on ice. If you are unlucky enough to experience this make no steering inputs and ride straight on through.
Ice - This is obviously dangerous. Much more so than in a car. So be incredibly alert to conditions that can cause ice. Early morning in the fall can be especially dangerous.
Snow- If you ride carefully, make minimal traction demands and remain smooth you will survive. I've ridden hundreds of miles in snow on high performance sport bike tires and managed to stay upright. But it isn't for the faint of heart. (not very common here in California, so no worries)