1.1 Speed Limits and Following Distance

Speed Is About Conditions, Not Just the Sign

The single most important idea Washington tests on speed is that the number on the sign is a maximum for ideal conditions, not a guaranteed-safe speed. The basic speed law in RCW 46.61.400 states that no person may drive faster than is reasonable and prudent under the conditions, considering the actual and potential hazards.

In heavy rain, fog, snow, gravel, or dense traffic, a reasonable and prudent speed can be far below the posted limit. A driver who hits the posted 45 mph in a downpour and loses control can be cited for "too fast for conditions" even though the speedometer never crossed 45. The knowledge test rewards the answer that adjusts speed to the conditions rather than the answer that clings to the posted number.

The rule cuts both ways. Driving far below the normal flow of traffic with no good reason can also be illegal, because a slow vehicle bunches traffic and tempts others into unsafe passing. On a multi-lane road you should keep right and let faster traffic pass on the left.

Posted and Default Speed Limits

Always obey the posted sign first. Where no sign is posted, Washington's statutory maximum limits in RCW 46.61.400 apply. Memorize these defaults because the test asks them directly.

Local authorities and the state may raise or lower these limits, so a posted sign always overrides the default. Speeds above 60 mph on state highways, and the 70 mph (or higher) seen on some freeways, exist only where specifically posted. If you see no sign on a city street, assume 25; on a county road with no sign, assume 50.

The 4-Second Following Rule

Tailgating is the leading cause of rear-end collisions, so Washington teaches a time-based gap rather than a fixed car length. The Driver Guide recommends a 4-second following distance. To measure it, watch the rear bumper of the vehicle ahead pass a fixed object — a sign, pole, or pavement shadow — then count "one-thousand-one, one-thousand-two, one-thousand-three, one-thousand-four." If the front of your car reaches that same object before you finish counting, you are following too closely and must drop back.

Four seconds is the minimum for good conditions. Add seconds whenever stopping is harder or seeing is harder:

• Rain, fog, or snow — traction and visibility are both reduced.
• Following a motorcycle — it can stop faster and may slow without a bright brake light.
• Towing a trailer or carrying a heavy load — your own stopping distance grows.
• Being tailgated — increase the gap ahead to give yourself room to brake gently.

Total Stopping Distance

The distance it actually takes to stop is not just the braking distance. It is the sum of three parts that happen in sequence:

1. Perception distance — how far you travel while your eyes and brain notice the hazard.
2. Reaction distance — how far you travel after you decide to brake but before your foot presses the pedal.
3. Braking distance — how far the vehicle travels after the brakes take hold until it stops.

Total stopping distance = perception + reaction + braking. Two facts make this exam-relevant. First, perception and reaction distance grow when you are tired, distracted, or impaired — alcohol and phones lengthen the first two parts before the brakes are even touched. Second, braking distance grows with the square of speed: roughly speaking, when you double your speed the braking distance quadruples, and on wet or icy roads it grows even more because the tires have less grip. This is exactly why the basic speed law and a larger following gap matter most in bad weather.

Worked Example: You are driving 40 mph on a dry road and a deer steps out. You travel during perception (about 0.75 second) and again during reaction (about 0.75 second) before you even touch the brake — at 40 mph (≈59 feet per second) that is roughly 44 feet of perception distance plus 44 feet of reaction distance, about 88 feet gone before braking begins, then braking distance on top of that. Cut the same scenario into the rain and the braking distance can easily double. The lesson is not the exact feet but the principle: most of your stopping distance is used up before the brakes ever work, so leave room and slow down for conditions.

Space Management

Good drivers manage a cushion of space on all four sides, not just ahead. Keep the 4-second gap in front, stay out of other vehicles' blind spots beside you, avoid letting a tailgater push you, and never box yourself in where you have no escape path. If a hazard appears, the side with open space is your way out.

Parking Distances and Parking on Hills

Washington (RCW 46.61.570) forbids parking within set distances of certain features. The three numbers tested most often are:

• 15 feet of a fire hydrant.
• 20 feet of a crosswalk at an intersection (marked or unmarked).
• 30 feet of a flashing signal, stop sign, yield sign, or traffic signal.

You also may not park within 50 feet of a railroad crossing, in front of a driveway, on a crosswalk, or in a way that blocks traffic. When you park on a hill, turn the wheels so a runaway vehicle would roll away from traffic: downhill, turn the wheels toward the curb; uphill with a curb, turn the wheels away from the curb so the tire rests back against it; with no curb (either direction), turn the wheels toward the edge of the road. Always set the parking brake.