Today is Sunday, and it's a chill one. No big to-dos on the agenda, so after battling a friend on Lichess for a few hours, I walk out of my condo to grab some snacks at the supermarket around the corner. As I stroll past one of the condos in my neighborhood, a car approaches. I can see it's about to turn into the driveway—which crosses the sidewalk.
I stop.
The car stops.
The driver waves at me.
I look at him, nod my thanks, and walk briskly—even breaking into a little fake jog—across the driveway to the safety of the continuing sidewalk.
Situations like this happen to me all the time. And every single time, I have the same thought: Nice of him, I think to myself. But honestly? I would have much preferred if he'd just kept driving. Why do I think that?
Let's break down the car-pedestrian scenario with three possible outcomes:
A: Car doesn't stop → Pedestrian waits
B: Pedestrian doesn't stop → Car waits
C: Both stop, then one gives the other the right of way
(Let's ignore option D: Nobody stops and there's a crash)
Right off the bat, it's clear that scenario C is the most time-inefficient. To illustrate this timing-wise, let's assume that both stopping and crossing each take 5 seconds for both the car and pedestrian. The time for our scenarios breaks down like this:
t_A = 5s (car doesn't stop while pedestrian waits) + 5s (pedestrian walks) = 10s
t_B = 5s (pedestrian doesn't stop while car waits) + 5s (car drives) = 10s
t_C = 5s (both stop) + 5s (one crosses while the other waits) + 5s (the remaining party crosses) = 15s
It becomes clear that in scenario C, both parties lose 5 seconds. In reality, the back-and-forth of nonverbal negotiation over who goes first can often take even longer! I've experienced way too many situations where drivers insist on being polite, but so do I. Sometimes the situations get so absurd that I take a step forward, the driver hits the gas at the same moment, we both stop, and the whole Russian roulette starts over again!
But there's another aspect we can factor in here: energy. Back in school, I learned that Newton's first law of inertia states that an object will maintain its state of rest or motion unless acted upon by forces like friction. To brake a moving object, opposing energy must be applied. Plus, energy is also needed to get something moving again! How much energy does this cost for a car versus a pedestrian? I asked Anthropic's latest Claude Sonnet 4 model:
Car:
- Speed: 30 km/h = 8.33 m/s
- Braking distance: 15 m
- Mass: 1,500 kg
The kinetic energy that must be dissipated works out to E = ½mv² = ½ × 1,500 kg × (8.33 m/s)² = 52,000 J (52 kJ). To accelerate back up requires a similar amount of energy, so the total cost per stop comes to roughly 2 × 52 kJ = 104 kJ.
To put this in everyday terms of gas consumption: With gasoline having an energy content of 32 MJ/liter and an internal combustion engine efficiency of 25%, we get usable energy of 32 MJ × 0.25 = 8 MJ per liter. Per stop, this leads to consumption of 104 kJ ÷ 8,000 kJ/L = 0.013 liters = 13 ml of gas. Doesn't sound like much?
Pedestrian:
- Speed: 4 km/h = 1.11 m/s
- Braking distance: negligible
- Mass: 70 kg
Stopping costs our pedestrian a whopping 43 J. This is partially absorbed by muscles, so it's not entirely lost energy. By the way: assuming that accelerating requires about the same energy effort in the legs, then a person uses roughly 2 × 43 J = 86 J per stop. Note: we were talking kilojoules for the car—that's three orders of magnitude difference.
4,184 kJ = 1 kcal is the physical definition of a kilocalorie. Our pedestrian needs 0.086 kJ per stop, which converts to 0.086 kJ ÷ 4,184 kJ/kcal = 0.02 kcal. 0.02?! I'm surprised—anyone who's ever read the back of a cereal box knows that's basically nothing. Stopping feels so much more taxing—maybe that's a mental effect, but let's ignore that in our little calculation.
Okay, thanks to AI we now have concrete numbers. But now for the million-dollar question—how many liters of gas have been consumed through stop-and-go interactions between me and cars at unsignalized intersections throughout my entire life, because cars stop even though I'm letting them go first? I'll leave out how many calories I've burned from my stopping, since at 0.02 kcal per incident, I'd probably barely rack up more than one extra-small low-carb yogurt cumulatively.
Cars stopping even though I'm waving them through happened to me occasionally on my way to and from school, but not that often. In college, I moved to a city with lots of intersections, and the incidents multiplied. Now I live in Singapore, and both on my little street in the Balmoral neighborhood and when jogging or walking to work in the mornings, I often stop and wave cars ahead, only to have them be nice enough—or foolish enough—to stop too. If we average it out over, say, the last 15 years since before that I wasn't a serious pedestrian, I'd estimate about 3 such encounters per week. To be conservative, let's say 2. So: 2 per week × 4 weeks × 12 months × 15 years = 1,440 unnecessary stops. 1,440 × 0.013 liters = 18.72 liters.
And how much time has been lost for both me and the drivers? 1,440 × 5s = 7,200 seconds = 120 minutes = 2 hours. Unbelievable! Exactly 2 hours.
The bottom line:
Through the over-polite stopping of cars that I wanted to let pass at driveways and other types of unsignalized intersections, each of us has lost 2 hours (which really should be counted independently too). Plus, aside from my tired thigh muscles, roughly 20 liters of gas have been burned. Based on average gas prices over the last 15 years, that's about €30.40 of wealth that just went up in smoke.
Dear drivers: I know you mean well. But next time when you see me standing at the curb with my AirPods in, looking at you expectantly, please don't stop.