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Dr. Diandra: How NASCAR monitors pit road speed

Before NASCAR implemented electronic scoring in 1993, each team designated an official scorer to manually tally laps. If there was any disagreement, NASCAR could compare their records to the teams’ numbers. Scoring on paper mostly worked fine — except when crashes scrambled the field and the control tower had to scramble to get the cars back in the proper order.

Today, computers keep track of how many laps each car completes and where the cars are on the track. The system also records the details of pit stops -- how long it takes drivers to get to and from their pit boxes, and how long the car stays in the pit box.

And although electronic scoring puts human scorers out of work, it helps NASCAR enforce a critical safety rule: pit road speed limits.

Getting loopy

The same electronic timing system monitors the track and pit road. Electronic timing systems are so ubiquitous (and affordable) that even small racetracks employ them.

An electronic scoring system requires two components. The first is a collection of wire loops embedded about a foot below the asphalt surface. The number of loops around the track increases as the track length increases. At facilities where timing loops were retrofitted, you can sometimes see two grooves cut into the asphalt, as shown in the photo below from Charlotte Motor Speedway.

A photo of Charlotte Motor Speedway's pit road, with scoring loops indicated by red arrows

Timing loops are hidden by asphalt at other tracks, but the loops don’t need to be visible to work.

The other component of the scoring system are the transponders every car must carry. The transponder mounting points for the Next Gen car are on either side of the front of the fuel cell. Each transponder emits a unique, short-range electrical signal.

The wire loop in the track acts as an antenna that captures the car’s transponder signal. The signal travels to a computer, which records the car’s identity, the location of the triggered loop, and a timestamp. While the system is wireless, it has a fiber-optic backup.

NASCAR uses the data collected from this system to provide fans with loop data, which generates additional insights about driver performance. Race control, however, uses the loop information in real time. After an accident, NASCAR lines up the cars for the restart according to their positions as recorded by the scoring loops. Loop data lets NASCAR make sense out of even the most confusing multi-car crashes.

Looping in pit road

The scoring loops have to extend to pit road so that pitting cars are credited with a lap when they pass the start/finish line. But NASCAR also uses a denser grid of scoring loops on pit road for the safety of the crew members who service the cars.

Pit crew members experienced close calls last week at World Wide Technology Raceway at Gateway, which has the narrowest pit road of any track on the Cup Series circuit. During the Coca-Cola 600 the week before, Denny Hamlin clipped Tanner Andrews, Joey Logano’s front tire changer.

NASCAR implemented pit road speed limits in 1991, following tire changer Mike Rich’s death at the 1990 Atlanta Journal 500.

In 2022, pit road speed at tracks hosting points races ranges from 30 mph at smaller tracks like Martinsville and Bristol to 55 mph at 2-mile and larger ovals. Road course races, like this week’s at Sonoma, have a 40 mph pit road speed limit. However, NASCAR allows a 5-mph tolerance, so the effective pit road speeds range from 35 mph to 60 mph.

As an example, let’s consider the pit road loops at Pocono. We have detailed information about how the configuration changed between the two races in 2012. The second 2012 race featured an unusually large number of pit-road speeding penalties.

According to Jose Blasco-Figuroa, lead race engineer for Daniel Suárez, NASCAR provides teams with maps showing where scoring loops are on the track and on pit road. Although NASCAR doesn’t draw pit maps to scale, having a realistic model helps to understand the measuring process. The graphic below is my rendition of the information.

A graphic showing the pit road at Pocono showing the locations of scoring loops

The first thing to realize is that, although NASCAR rules reference pit-road speed, NASCAR doesn’t actually measure cars’ speeds. NASCAR measures time and uses basic physics to get speed.

The relationship between time, distance and velocity is easy to remember. You just follow the units. Speed is miles per hour: distance (miles) per (a.k.a. divided by) time (hours).

An equation relating speed to distance and time

On our Pocono example, let’s look at the segment from the loop I’ve labelled P10 to the loop labelled P11 — although the analysis works for any two timing lines. The distance between loops P10 and P11 is 103.25 feet. A car traveling at exactly 60 mph would take 1.173 seconds to traverse that segment.

When a car comes down pit road, its transponder notifies the computer when it passes scoring loop P10. It does so again when the car passes scoring loop P11. The computer records the times at which each loop triggers, then subtracts the two times. If the difference is less than 1.173 seconds, the driver was speeding. NASCAR alerts the crew chief as to the infraction and which segment of pit road it happened in as soon as the violation occurs.

Average speed means strategy

Off the track, speed limits are enforced with radar guns or LIDAR, which measure instantaneous speed. Instantaneous speed is -- just as it sounds -- speed at a particular instant. If law enforcement catches you going over the speed limit at any time, you’ll get a ticket.

Scoring loops measure average speed rather than instantaneous speed. While this sounds like an academic distinction, it’s actually useful. A driver can meet an average speed limit more than one way.

If you travel 60 miles on a highway with a speed limit of 60 mph, you’ll cover those 60 miles in one hour. You could go 60 mph the whole way. You could drive 55 mph half of the time and 65 mph the other half. Or you might get stuck in a traffic jam, then speed to make up the lost time. You can utilize any one of these strategies and still complete 60 miles in one hour. You can use any of these approaches to have an average speed of 60 mph.

Having to meet an average rather than an instantaneous speed is why drivers sometimes speed up or slow down suddenly on pit road. They know exactly where the timing lines are. They use that knowledge to gain precious seconds getting to and from their pit boxes.

A pit box with a timing line inside it is a big advantage. At least one segment will include the time during which the car is stopped. That allows the driver to go well over the speed limit coming in or going out of the box. There’s no possibility, given 10-plus seconds sitting still, the driver can reach a high enough speed to exceed the average speed limit. But they do have to make sure they slow down before the next segment.

That, incidentally, is one reason why NASCAR added timing lines to many pit roads: Some pit boxes offered significant advantages because of their locations.

When competition is close, small advantages on pit road make an even bigger difference.