One of the most common penalties in a NASCAR race is speeding on pit road. In 2020, 78.7% of all driver pit-road penalties were speeding. So how does NASCAR measure and assess pit-road speeding penalties?

## How Does NASCAR Know Where the Cars Are?

Back in the day, one person for each car was the official ‘scorer’. He (or often she) marked the car’s position every lap. Nowadays, however, the process is entirely automatic.

Scoring loops are embedded in every NASCAR track. You can identify them pretty easily. It’s not like NASCAR is trying to hide them.

There are two lines because these are literally loops of wire in the track. Loops, because that’s a requirement for electromagnetic induction.

Back in 1830, Michael Faraday observed that a magnet moving through a loop of wire produces a current in the wire. That’s with no battery or other source of electricity.

Each car carries a transponder, located just a little forward of the driver’s seat, inside the door. Each time a transponder goes over one of these scoring loops, it sends an electrical signal. Every transponder is unique, which allows the people in timing and scoring to tell which car is which.

Yup. Here’s the scoring-loop diagram for Pocono back in 2012. I mention that it’s 2012 because NASCAR added scoring loops to Pocono in 2016. Apparently, a number of teams didn’t catch the change. That resulted in a race with an enormous number of pit-road speeding penalties.

## What Do They Measure?

The scoring loops blip when a car passes by. So they are measuring the time it takes for a car to travel between two scoring loop. They know the distance between the two loops, so you use:

speed=\frac{distance}{time}

to get the speed.

But note that this measures average speed over the timing segment, not instantaneous speed.

Instantaneous speed is (just as it sounds) your speed at a particular instant. Radar guns measure instantaneous speed. On the expressway, you can get a ticket if you go over 65 mph at any instant.

In NASCAR, average speed is the important thing.  Pit Road speed at Pocono is 60 mph.  You can go 50 mph for half the time and 70 mph for half the time and your average speed would be 60 mph.

In fact, the graph at left shows five speed vs. time traces. Each has the same average speed, but the instantaneous speeds vary all over the place.

That’s why you see drivers playing all those games with speeding up and slowing down. They don’t have to be at or below pit road speed at every moment in a given segment. Only the average speed matters.

## So That’s Why They Pick Pit Boxes with Timing Lines in Them?

Again, Yep.

If you spend twelve seconds inside your pit box, you can speed out of it without any worry that you’re going to have an average speed higher than the limit. That’s one reason that NASCAR added timing lines on many pit roads: some pit boxes had significant advantages because of where they were located.

## Are Timing Line Locations Secret?

A Pit Road map showing timing lines is available to the teams and the media. Before that was common, crew chiefs walked the track to find them. No effort is made to hide their locations. Ralph Shaheen tweeted the Pocono map during the race to help explain what was going on.

Note that NASCAR doesn’t draw their maps to scale.

## What’s with This 5 mph ‘Tolerance’?

Back in the day, they used varying measurement instruments with varying accuracies. The 5 mph tolerance is a relic from that period. If Pit Road speed is 55 mph, it’s actually 60 mph. But if you’re 60.01 mph, you will get a penalty.

## How Often Does NASCAR Move Timing Lines?

Given that they are embedded in the track, moving timing lines is a major undertaking. It’s not like moving a garden hose.

If I were repaving a Pit Road, I would play it safe and put in a whole bunch of them. Then you have some leeway for the future.

## Are Some Tracks More Conducive to Pit Road Speeding?

There are two reasons. The first is that track position is more important at some tracks than others. Drivers might be willing to chance a penalty if they can make up a good number of positions.

The other reason is when tracks are small enough that pit road has to extend into the turns. Let’s look at the penalties for the Spring 2021 Phoenix race.

Remember that they’re measuring time and inferring speed. When you’re on a curve, though the distance you travel isn’t constant.

It’s the old marching-band problem. When a band has to turn, the people on the outside of the turn have to walk much faster than usual. The people on the inside of the turn almost march in place. That’s the only way to keep the line straight.

The same thing happens here. Let’s say two drivers travel at the same speed, but one is on the outside of the turn and the other is on this inside. The outside driver takes longer than the inside driver. So, given how NASCAR measures, it’s possible for one of them to ‘speeding’ and the other not — even though they were going the same speed.

That’s something the driver has to figure out. Not having practice doesn’t help new drivers figure it out.

## Can’t They Just Give the Drivers Speedometers?

Because tachometers are more accurate than speedometers.  You can tell your speed to a fraction of a mph with a good tach.

The divisions on a tach are usually 100 rpm. If the driver can read the gauge to 100 rpm, for a typical gear ratio (i.e. let’s say a 1.45:1 second gear and a 4.22 rear end gear), each 100 rpm step on the tach corresponds (for 82.1 inch circumference tires) to 1.37 mph. If you assume that the driver can read the tach to 50 rpm, that’s 0.64 mph.

Besides – when drivers get caught speeding, it is usually because they were trying to cut it too close to the limit, not because they didn’t know how fast they were going.  Remember that you are being judged on average velocity and both the tach and a speedometer measure instantaneous velocity.

I’m not a fan of relying too much on a row of lights that goes red if you’re over or close to over. I’ll take a dial over a light any day (as long as it’s a BIG dial). Drivers have many things going on and light may make their lives much easier, but a light is never as accurate as a dial.

## Why Penalize Someone for Going 0.01 mph over the Effective Pit Road Speed Limit?

A.  Where do you stop?  If you tell them you’re giving them another 0.1 mph, then the person who gets caught going 0.11 mph over the effective limit will complain that he was only 0.01 mph over the limit. You have to draw a line. Everyone races under the same conditions, so where the line is placed really doesn’t matter.

## Why Don’t They Show Pit Road Speeds?

I addressed this before in more detail – just my opinion, of course.  The more data NASCAR hands out, the more they’ve got fans picking apart every aspect of the sport.  I watch races with timing and scoring on my computer, twitter, the radio going over the TV, etc.  I like love data.  At some point, though, you want people watching the race and cheering on their favorites, not picking every millisecond of data apart. It’s a good race for me when I don’t want to look away from the television.

## Are Some Segments More Likely to Catch Drivers?

Short segments seem to be trickier. For an 80-foot segment going 60 mph, you only spend 0.947 seconds in that segment.

At 60 mph, you spend 2.3475 seconds in a 210-foot segment.  Let’s say you’re going 60.06 mph.  In the short segment, you would spend about one millisecond (one thousandth of a second) less in the segment.  In the long segment, you save 2.3 milliseconds in time.

Shorter segments are also less forgiving.  If you push too hard on the throttle for an instant, consider how that affects the average speed if that instant is out of 2.3 seconds or 1 second.  The drivers are constantly trying to figure out how to get maximum speed within the boundaries of the timing and scoring system.

I'm a recovering academic who writes about the intersection of science and life. I'm interested in AI, advanced prosthetics, robots and anything that goes fast. Author, THE PHYSICS OF NASCAR and Editor, BIOMEDICAL APPLICATIONS OF NANOTECHNOLOGY

1. bob emmons says:

By the same token, how about if the last segment was 79 feet 11 inches??????

2. Diandra says:

Hi Bob – back in the USA?

Are you asking about the time difference if the segment was a slightly different length?

3. Eric Kimbarl says:

The speed limit was set for safety reasons for the pit crews, so going 70 to 75 mph then 40 to 45 at other times on the pit stop to average out to a given mph, doesn’t keep the pit crews safe when they are going faster than the speed limit.

• Eric: That is a really good point. Playing around with trying to game the timing lines isn’t helping preserve safety on Pit Road.

4. Steve Barr says:

If the transponders are located away from the front bumper, and the driver is timing his “clear of pit road” based on the bumper crossing the line, there must be an offset between the actual scoring loop and the painted line. Could there be some error here? Especially in a very short segment, it seems like a little bit of measurement error could make a large difference.

• Steve: Definitely an issue. I don’t about professional drivers, but I do a pretty lousy job of estimating where my bumpers are when I’m trying to park. I think the key thing here is, as you point out, the shorter the segment, the more of an issue it is. It would be helpful to find out how long the segments are at the short tracks. The have fewer segments, but I wonder if they have any that are 83 feet? Anyone know?

5. Bob says:

I have a feeling that with such a short loop that such little details as just raising the tire pressure a little could have advanced the speed enough to through the tach reading off. They aim to get SO close to the 60mph that there’s very little margin for error. They setup the christmas tree lights on the tach pre-race and i don’t think they can adjust them after (easily). The driver just knows if they see red they better lift. I know that NASCAR used to overstate the accuracy of their numbers, not that long ago you could look at their “Margins” between cars and you’d see (0.06, 0.13, 0.19, 0.26) as the margins…which jumps out pretty quick to show that last figure was pretty much a barely significant figure so to speak.

Teams will likely just have to set a higher tolerance (margin of error) when having a segment so short…the slightest issue in terms of mis-measuring the distance of those last lines could have caused the same issue…if those lines aren’t completely parallel (like i think TV has shown they aren’t on some tracks…go figure) cars running to the inside or outside of pit road may have been at a marginal disadvantage to get tagged.

6. FranInAtlanta says:

If you map the speeding penalties onto the pit road stalls, you will see three areas took the repeated hits. I’m betting something about the sensors under pit road being screwed up.

7. djones says:

Hi Dr, D,

As usual, you explained the pit road speeding issue so I can understand it. I did find it strange that some of the teams didn’t pick up the map showing where the loops were. I bet that doesn’t happen again.

8. just tim says:

The teams are all very well versed about the hows and whys of the speed limits. Teams often use this to their advantage a la Keselowski who at a race last year passed several cars on pit lane to take a lead by travelling more than doubling pit road speed simply because he had the last pit stall – a stall which was part-way into the last timing zone – and the 14 or so seconds spent servicing the car in that zone meant he couldn’t possibly be over the “average” speed limit no matter how fast he exited. What is overlooked here is that although NASCAR provides these sheets to any chief that asks for them, NASCAR changed the configuration at Pocono without the courtesy of a “heads up” to the teams. The previous loop-layout was in place for years and teams like the 48 had that layout nailed. It is inexcusable that NASCAR would change parameters without communicating that to the teams.

9. bob emmons says:

Yes. Since i’ve retired, i’m not up to the math, but you like that sort of thing.

10. John says:

According to the tweeted photo there was “only” 16 speeding penalties, the rest came from pitting too soon and not obeying NASCAR’s request. Yet the official number of speeding related penalties is 22…
What am I missing?

• John: Nate Ryan tweeted that photo midway during the race. That was an interim report and not the final one. Thanks for asking – I should have been clearer about that.