A Byte of Wall StreetInteractive · from the Fast Lane video

your car prefers the left lane other drivers tap the strip to look elsewhere

Lane speeds · timed stretch

Your car

Waiting for your car to reach the road…
Real data · not the simulator

On US-101, the left lane was the slowest place to sit

NGSIM camera-tracked vehicle trajectories, Los Angeles, 15 June 2005, 7:50–8:35 a.m., about 1,800 ft of freeway, 4,404 cars, average pace about 21 mph. Cars that stayed in one main lane, seconds per mile against same-minute traffic (negative is faster):

  • The far-right main lane was the fastest main lane in 9 of 9 five-minute windows; the left lane was the slowest in 7 of 9.
  • The left lane held about 15% more vehicle-time than the right lane and ran about 17% slower.
  • Changing lanes barely paid: cars that used three or more lanes were 2.6 s/mile faster than same-minute traffic, cars that never changed were 2.0 s/mile slower.

One freeway, one morning, and drivers chose their own lanes, so this describes what happened rather than proving why. The simulator above is for seeing the mechanisms; quote these numbers, not its.

How the simulator works

Small rules, every car

  • Each car follows the Intelligent Driver Model (Treiber et al., 2000): it keeps a safe time gap and brakes smoothly. Desired speeds average about 69 mph.
  • Lane changes use MOBIL (Kesting et al., 2007): change if it helps you more than it costs the drivers behind. Drivers also chase a lane that looks faster ahead, accept a short gap right after changing, and get let in when they signal for a forced merge.
  • One car in ten is a test driver: equal numbers stay left, middle, right, or weave, and they drive the same way otherwise. You ride one of them.
  • Each test car's time over the timed 2.5 miles is compared with ordinary cars that entered within a minute of it, the same method used on the real data.

It is a port of the Python model from the video, checked against field data for lane speeds in light traffic and the speed of stop-and-go waves. Real traffic has more going on, so treat its numbers as direction, not size.