In a motor vehicle collision where the parties dispute liability, they usually are disputing the time, speed and distance of the vehicles. So you need to be able to calculate how far a vehicle will travel in a second at any given speed.
As any accident reconstruction textbook will underscore, people usually overestimate the time it takes for a car accident to unfold. In one study, participants who viewed a thirty-second event estimated an average duration of 150 seconds, 500% longer than it actually took.
You can also figure this out by just asking someone to estimate how many feet a vehicle travels in one second while driving 65 mph. The range of responses is laughable, and this is what lawyers get from fact witnesses.
This typically works to the victim’s advantage, particularly with respect to speed. Why? Because the longer a visual estimation takes, the slower the vehicle must have been traveling.
Sample Time Speed Distance Cross Examination
This is an example of how easy it can be to trip up a witness on cross examination with very simple math:
Q: When you first saw the Plaintiff, how far away was he from your vehicle?
A: I’m not sure. I didn’t have a tape measure.
Q: So you’re saying you have no idea? You can’t even offer an estimate?
A: Maybe 40 yards.
Q: Forty yards? Could it have been more, say, 50 yards?
A: I guess so.
Q: What about 60 yards? Could that be possible?
A: I don’t know. Again, I didn’t have a tape measure.
Q: Alright. Now, how long would you say it was from the moment you saw the Plaintiff until the impact occurred?
A: Maybe a second.
Q: A second? So, you would agree that a vehicle traveling at 30 miles per hour is moving at about 2 miles per minute, right?
A: Yes.
Q: And just to be clear, you’re aware that there are 1,760 yards in a mile, correct?
A: Yes.
Q: So at 30 miles per hour, your vehicle would have been traveling at around 15 yards per second, wouldn’t it?
A: I suppose.
Q: So if the Plaintiff was really 40 yards away when you first saw him, and you were traveling at 30 miles per hour, you would have had almost three full seconds before impact, correct?
A: I guess that sounds right.
Q: And if the Plaintiff was actually 50 or 60 yards away, as you admitted was possible, then that would give you even more time—about three to four seconds—before impact, right?
A: I’m not sure, but I suppose.
At this point, you’ve established a key contradiction in the defendant’s testimony. Initially, the defendant suggested that he only had about a second before impact, but the basic math based on his own estimates of distance and speed suggests that there were several seconds available to react. This discrepancy severely weakens the defendant’s credibility, as it exposes the inconsistency in their version of events.
Additionally, the defendant’s inability to provide a consistent estimate of the distance between the vehicles (ranging from 40 to 60 yards) further highlights the unreliability of their testimony. Combining this with the timeline of events, as demonstrated by the vehicle’s speed, allows you to strongly argue that the defendant either misjudged the situation or is not providing an accurate account, which could play a critical role in proving liability.
Certainly, you want to look for opportunities to exclude the argument that the plaintiff’s speed was not causally related to the accident or that the lay witness testimony is inadequate to support a finding of contributory negligence because of excessive speed. Argue Myers v. Bright, but be prepared for argument that the Maryland Court of Special Appeals opinion in Romero v. Brenes is controlling.
How to Calculate Vehicle Speed
This chart is a good cheat sheet for time, speed, distance calculations for how fast a vehicle is going per second.
- 1 mile per hour = 1.4667 feet per second
- 10 miles per hour = 14.7 feet per second
- 20 miles per hour = 29.3 feet per second
- 25 miles per hour = 36.7 feet per second
- 30 miles per hour = 44.0 feet per second
- 35 miles per hour = 51.3 feet per second
- 40 miles per hour = 58.7 feet per second
- 45 miles per hour = 66.0 feet per second
- 50 miles per hour = 73.3 feet per second
- 55 miles per hour = 80.7 feet per second
- 60 miles per hour = 88.0 feet per second
- 65 miles per hour = 95.3 feet per second
How Do I Calculate Speed and Distance in a Car Accident Case?
The formula for speed and distance is the same for a car as any other object: distance ÷ time. So if you want to calculate the speed of a car at sixty miles an hour, the math is (60 x 5280) ÷ (60 x 60) = 88 feet per second. So this formula works for any “how far do you travel?” questions.
Can You Calculate Vehicle Speed from Skid Marks?
You can roughly calculate the speed of a car or truck if you can measure the skid marker. The formula is the S² = Es² + 30fd. S is for the speed of the vehicle, Es is the ending speed, f is the drag factor and d is the length of the skid.
The formula is easy enough. Applying it is another matter. Calculating the ending speed, if the vehicle does not come to stop, is a challenge as is estimating the drag factor.
How Long Will Tire Marks Last on the Road After a Car Accident?
How long tire marks remain on the road after a car crash is dependent on a lot of variables. These variables include the tires, the weight of the vehicle, the wear on the asphalt or concrete, the type of braking system, the weather, and so forth. Tire marks can give you estimations of speed so you can answer the “How far do you travel at X mph in Y seconds?” questions.
The take-home message is if you are a car accident lawyer and you want to preserve physical evidence from a crash scene, you want to secure that evidence sooner rather than later.
How Long Does It Take a Driver to React and Hit the Brakes?
The average driver takes between 2.3 and 2.5 seconds to hit the brakes in a sudden emergency. Data suggests the average time to brakes is lower than 2.5 seconds if the driver perceives a critical sudden emergency. Younger drivers are typically quicker to the brakes than older drivers.
How Does Speed Impact Braking Distance?
The braking distance increases fourfold when you double the speed.
What Is Perception-Reaction Time, and How Does It Impact Accident Analysis?
A: Perception-reaction time refers to the time it takes a driver to perceive a hazard and begin taking action, such as hitting the brakes. On average, it takes about 1.5 seconds for perception and 0.75 to 1 second for the reaction, totaling 2.25 to 2.5 seconds. This can significantly impact the stopping distance, as the vehicle continues traveling during this time before any braking occurs.
How Do Road Conditions Impact Stopping Distance?
Road conditions are a real monkey wrench in these time, speed, distance calculations. Wet, icy, or uneven roads can increase stopping distance because tires have less traction on slippery or rough surfaces. For example, stopping on ice might take ten times longer than on dry pavement. Factors like rain, snow, gravel, or oil can all reduce the friction between tires and the road, leading to longer stopping distances and a higher chance of skidding.
This impacts skid mark analysis, too. Wet roads reduce tire friction, meaning that a car might skid further before stopping. Conversely, on dry asphalt, the marks may be more defined and shorter. These conditions must be considered when analyzing skid marks to estimate speed.
What Is Reaction Distance and How Is It Calculated?
Reaction distance is the distance a vehicle travels during the driver’s reaction time before they begin to brake. It can be calculated using the formula: reaction time (seconds) x speed (feet per second). So if a driver reacts in 2.5 seconds while traveling at 60 mph (88 feet per second), the reaction distance would be 220 feet (2.5 x 88).
Can the Extent of Vehicle Damage Indicate the Speed at Which a Car Was Traveling?
Yes, the extent and pattern of vehicle damage can provide clues about the speed at which a car was traveling. Accident reconstruction experts can analyze crush patterns, deformation, and displacement of vehicle parts to estimate the speed at impact. But, boy, you better have covered every base because what happens is experts doing these estimates make a lot of dumb assumptions and get crushed on cross-examination.
How Does the Weight of a Vehicle Impact Stopping Distance?
Heavier vehicles typically take longer to stop because they have more momentum. The greater the mass of the vehicle, the more distance it will need to come to a complete stop, all other factors being equal. This can be especially important in truck accidents where the vehicle’s weight drastically increases stopping distance.
How Can Witness Statements Help Calculate Vehicle Speed?
Witness statements can be crucial in calculating vehicle speed. Eyewitnesses can provide – at least in some situations – accounts of how fast a vehicle appeared to be traveling, its behavior on the road, and other factors such as whether the driver attempted to brake. While subjective, these observations can corroborate physical evidence and assist in the overall reconstruction of the accident.
Can You Estimate Vehicle Speed Using the Force of Impact?
The force of impact during a collision can provide valuable information about the speed at which the vehicle was traveling. This calculation often requires input from accident reconstruction experts who can use physics principles like momentum and energy transfer to estimate the speed based on the damage and impact force on the vehicles involved.
How Can Surveillance Footage Be Used to Calculate Vehicle Speed?
Surveillance footage can be used to calculate vehicle speed by analyzing the distance a vehicle travels within a certain timeframe. By knowing the frame rate of the video (frames per second) and measuring the distance traveled in the footage, experts can determine the speed. For example, if a car travels 100 feet in 2 seconds in the footage, the speed would be 50 feet per second (which translates to approximately 34 mph).
- Here’s a good time, speed distance calculator
- Good post on how to calculate speed at time of accident
- Cross examination of the Plaintiff’s expert on bias
- Sample cross examinations and other examinations of witnesses in personal injury case
- Maryland jury instruction on speed
- Getting ready for trial: more samples
- Overview of Maryland car accident lawsuits (what our accident lawyers do)