INDIANA FIELD GUIDE
Speed & following distance.
Leave time to recognize a problem and room to respond.
Always follow posted limits and reduce speed for hazardous conditions. The manual lists a passenger-vehicle maximum of 70 mph on rural interstates, subject to posted limits; trucks above 26,000 pounds declared gross weight have a 65 mph maximum there. These are not a reason to ignore lower signs or poor conditions.
The manual suggests at least two to three seconds behind the vehicle ahead as a basic following rule. Compare the time each vehicle passes the same fixed object. More space may be needed because of weather, traffic, or the kind of vehicle you are following.
Keep these in mind.
- Most urban residential areas have a maximum of 30 mph or the posted limit; alleys have a maximum of 15 mph or the posted limit.
- Obey lower posted school-zone and work-zone limits and their posted conditions.
- Allow at least three or four seconds when following a motorcycle. A rider may need room to maneuver around hazards.
- A tractor-trailer generally needs more stopping distance than a car. Do not cut closely in front of one to reach an exit.
Rules and worked examples.
Driving rules below summarize the official manual. Safety recommendations explain its practical guidance; example numbers are not additional legal requirements.
Driving rule
Following too closely is a traffic violation
Do not tailgate. The manual’s point table lists following another vehicle too closely as a six-point violation. Its two-to-three-second following guideline is a way to judge a basic gap, not a fixed legal minimum that makes every situation safe.
Example. Traffic slows while you are following a car. Ease off early and leave room instead of staying close to its rear bumper. If rain or visibility makes the gap unsafe, add more space even if you counted three seconds.
Why it matters. The rule against following too closely and the manual’s time-gap recommendation serve different purposes. A counted gap must still fit the actual conditions.
Safety recommendation
Measure following distance in seconds
The Indiana manual recommends staying at least two to three seconds behind the vehicle ahead as a basic following rule. This is a safety guideline, not a fixed legal distance or a guarantee of enough stopping room in every situation.
- Choose a fixed object beside the road, such as a sign or utility pole.
- When the rear of the vehicle ahead passes it, start counting seconds.
- Stop counting when the front of your vehicle reaches the same object.
- If the gap is too short, ease off the accelerator and rebuild space. Check again after traffic changes.
Example. The car ahead passes a pole. You count one second, two seconds, three seconds before reaching it. That is a three-second gap. If another car enters the space and your gap drops to one second, gently slow to restore room.
Why it matters. A time gap automatically represents more road distance at a higher speed. Counting car lengths does not adjust as clearly for speed.
Official manual: page 41
Safety recommendation
What three seconds means at different speeds
Using the manual’s distance-per-second figures, three seconds is approximately 154 feet at 35 mph, 242 feet at 55 mph, and 308 feet at 70 mph. These are rounded travel distances, not braking distances or statutory minimums.
Example. At 55 mph you travel about 80.7 feet each second. Multiply 80.7 by 3: a three-second gap is about 242 feet. A distraction lasting three seconds uses that much road even before you react to a hazard.
Why it matters. Total stopping space includes noticing the hazard, reacting, and braking. Vehicle weight, brakes, tires, pavement, slickness, and road grade all affect stopping.
Official manual: page 41
Safety recommendation
Add space for motorcycles, trucks, and poor conditions
The manual recommends at least three or four seconds behind a motorcycle. Leave additional space as conditions require, including slick pavement or poor visibility. Do not cut into a tractor-trailer’s stopping space.
Example. A motorcycle ahead moves around a pothole. A larger gap gives you time to notice the rider’s change in position. In rain, slow down and increase the gap further rather than treating three seconds as enough for every condition.
Why it matters. Motorcycles may react to hazards you have not noticed, and heavy trucks generally need more room to stop than cars.
Official manual: page 41, page 43, page 44, page 50, page 52
Driving rule
Posted limits and conditions both matter
Obey posted limits, including the stated conditions on school- and work-zone signs. The manual lists 70 mph for passenger vehicles on rural interstates, 65 mph there for trucks over 26,000 pounds declared gross weight, and 60 mph on rural divided state highways, subject to posted limits. Reduce speed for hazards rather than treating the limit as a target.
Example. A work-zone sign says 45 MPH WHEN FLASHING and its lights are flashing. Slow to the posted worksite limit before the zone. If rain or stopped traffic requires a slower speed, slow further. Another worksite may have a limit that applies at all times.
Why it matters. The number shown and the conditions printed on the actual sign govern that location. A statewide example is not permission to ignore a lower limit.