3.3 Speed Limits, Following Distance & Stopping Distance

The Posted Limit Is a Maximum

Speed limit signs show the maximum legal speed under ideal conditions. The manual says you should not drive faster than the limit and are responsible for always driving at a safe speed. It is safest to drive with the flow of traffic, up to the limit; driving much slower than other traffic makes vehicles pass you constantly, which raises crash risk.

Maryland's Basic Speed Law

Transportation Article § 21-801 says a person may not drive at a speed that, with regard to the actual and potential dangers, is more than what is reasonable and prudent under the conditions. It also requires an appropriate, reduced speed when approaching intersections where cross traffic is not required to stop, railroad crossings, curves, the crest of a hill, narrow or winding roads, and any special danger from pedestrians, weather or road conditions.

The manual lists conditions where you should slow down:

• Sharp curves or hills where it is hard to see.
• Slippery roads.
• Roads where pedestrians or animals may be present.
• Shopping centers, parking lots and downtown areas.
• Heavy traffic, narrow bridges and tunnels, and toll plazas.
• Schools, playgrounds and residential streets.
• Railroad grade crossings.

Why Speeding Is Dangerous

The manual says excessive speed does not save time and has severe effects because it:

• Reduces your ability to handle curves and avoid obstacles.
• Takes longer to stop.
• Decreases your ability to recognize and react to hazards.
• Makes it harder for others to judge your distance.
• Increases the force of a crash, so serious injuries and deaths are more likely.

Maryland Statutory Speed Limits (When No Sign Is Posted)

Limits above 55 mph may be set only on interstate highways and expressways, and no Maryland limit may exceed 70 mph.

School Zones and Speed Cameras

The State Highway Administration or a local authority may set a school zone within a half-mile of a school, post its limit, and double speeding fines there. Speed cameras in school zones may operate Monday through Friday from 6 a.m. to 8 p.m. and record vehicles going at least 12 mph over the limit. Civil penalties are tiered from $40 (12 to 15 mph over) up to $425 (40 mph or more over). A camera citation is not a moving violation and carries no points.

Points for Speeding

The MVA assesses 1 point for most minor violations, 2 points for speeding 10 mph or more over the limit, 5 points for going 20 mph or more over a 65 mph limit, and 6 points for speeding 30 mph or more over the limit.

Following Distance: The 3-to-4-Second Rule

Most rear-end crashes are caused by following too closely. The MVA recommends a minimum following distance of 3 to 4 seconds under ideal conditions:

1. Pick a fixed reference point ahead, such as a bridge, overpass, sign or mile marker.
2. When the car ahead passes it, count "one thousand one, one thousand two, one thousand three."
3. If you reach "three one thousand" or more before your car reaches the object, you are at least 3 seconds behind.

Increase it to 4 or 5 seconds, and possibly more, when following vehicles that stop often, such as buses and delivery vans. Leave much more space on wet roads, and even more on snow or ice. Following too closely carries 2 points.

Stopping Distance

The manual lists what determines how far you travel before stopping:

• The time it takes you to see that there is a dangerous situation.
• The type and condition of the road.
• The condition of your tire treads.
• The condition of your brakes.

Total stopping distance is the distance you travel while you perceive and react, plus the braking distance. The table below is an illustration only, assuming a 1.5-second perception-and-reaction time on dry pavement.

$$\text{Braking distance} \propto v^2$$

Because braking distance grows with the square of speed, doubling from 30 to 60 mph roughly quadruples it, from about 45 feet to about 180 feet. Wet, snowy or icy pavement makes every number longer.