November 7, 2025
Brake up the fight
Understanding traffic
Speed isn’t flow: Comments explode over bottlenecks, bikes, and tolls
TLDR: A viral explainer says jams happen because bottlenecks cap how many cars pass, not because drivers can’t go fast. Comments erupted over the claim that 30–35 mph moves the most cars, the idea that widening fails at stoplights, pro-toll arguments for congestion pricing, and skepticism about bike-lane capacity.
A bike-commuting blogger just poked the bear with a plain-English breakdown of traffic: it’s not about how fast roads let you go, it’s about how many people squeeze through at once. In their post, the shocker was that car lanes move the most cars around 30–35 mph, not at freeway speeds. Cue the gasp: one reader blurted that means interstates are built for speed, not actual throughput. The crowd went wild.
Then came the bottleneck bombshell. With traffic lights controlling flow, one slow signal can kneecap a whole corridor, and widening lanes won’t save you if a light only lets so many cars through. Commenters latched on, chanting “you can’t widen your way out of this,” while the “just add a lane” crew fumed.
Things really popped when the post said trains and even busy bike lanes can move more people per lane than cars. Skeptics rolled in: one questioned the bicycle density claims—especially with trailers—while bike fans pointed to real-world videos and “kids popping wheelies” jokes.
And then came the economists. A bold voice pushed dynamic congestion pricing—make busy roads cost more when they’re busy to keep them flowing—framing every extra car in a near-jam as a delay bomb for everyone behind. The thread split into camps: toll hawks vs. freeway purists, with memes, eyerolls, and plenty of “you ARE traffic” energy fueling the flames.
Key Points
- •Road throughput, not speed limit, governs travel time under congestion.
- •A single lane’s realistic capacity is about 1,800 cars per hour (one car every two seconds).
- •Car throughput is maximized around 30–35 mph due to stopping and following distance constraints.
- •Transit and bicycles can move more people per lane than cars under proper operation.
- •The tightest bottleneck (e.g., signal timing) sets end-to-end road throughput; queues grow when arrivals exceed green capacity.