Regulatory signs advise you of the maximum speed when all conditions are ideal. You must assess and adjust your speed to the:
- driver condition (fatigue, stress, illness, distraction)
- vehicle condition (tires, brakes, lights, wipers, weight, length, height, type)
- light condition (overcast, sunny, dark, glare)
- weather condition (snowing, blizzard, raining, windy, fog)
- road condition (gravel, potholes, icy, wet, curves)
- traffic condition (vehicles, pedestrians, cyclists, density)
Traffic tempo: You must set your speed according to the existing conditions but, at the same time, match your vehicle's speed to the traffic tempo. If you drive faster than the traffic flow, you are increasing your chances of having a collision. You are continually reducing your safe following distance, thus losing stopping space in front. You make more lane changes to thread your way past the vehicles ahead, increasing your chances for a collision. Driving decisions are increased because you are creating more driving problems, thus increasing the likelihood of a wrong decision. Faster driving will result in faster mental fatigue. Reading the traffic pattern requires you to scan the full picture ahead and to the sides by moving your eyes. The faster you push through traffic, the more rapid the scanning process, building tension and fatigue.
If you travel appreciably slower than the tempo of the traffic, you increase your collision chances from behind and from the sides. Vehicles following too closely behind you create hazards. Vehicles overtaking and cutting in are continually occupying your stopping space.
If your stops are gradual, you give the driver following you adequate notice of your speed reduction.