this post was submitted on 30 Sep 2023
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Even with single people in cars you can move wayyyy more than 100 people per hour in the top left.
Assume 25 mph speed and 30 feet between cars, each car crosses 30 feet in about a second. 3600 seconds in an hour, times 2 for both directions and you have 7200 people that can move on that little road.
Now add additional passengers…buses…it can move a decent amount more. There’s lots of reasons cars suck but let’s not make up math to prove the point.
It's not saying that the top row can support at most 100 people.
Just that if you have 100 people per hour, you need something like what's in the picture. The train tracks aren't being fully utilized in the top pic, either.
As an aside, you're forgetting that cars are ~15 feet long on average. So you've got an hour of traffic with consistently 1 car following distance, which is fairly unrealistic. Real world capacy of a lane is closer to 2k people per hour, or 4k both directions.
Yeah and the big road below can hold WAY more than 10,000 too. The numbers here are all made up and it doesn’t really do a good job of making the point the creator wants to make.
Yeah.
I think I count 23 lanes in the bottom pic.
Ignoring the effect of heavy vehicles and assuming a free flow speed of 70, the federal highway authority's numbers would be 2400 vehicles per lane or 55k vehicles per hour. Assuming an average occupancy of 1.5 people per vehicle, that's nearly 83k.
I'm having trouble finding actual sources right now for max rail capacity, but https://en.m.wikipedia.org/wiki/Passengers_per_hour_per_direction claims 60-90k passengers per direction on 3.5 meter lanes for "suburban rail".
Although 83k people per hour is 41.5k people per rail track. Assuming a 360 person train like the Bombardier BiLevel Coach, that's only 115 train cars per hour per track. If each train has 11 cars, that's 10 trains per hour or a train every 6 min. Not really that unreasonable, and the tracks will look mostly empty unlike that monstrosity of a road.
The road in the bottom picture seems to be jammed. 23 lanes are no use if there's a bottleneck at the end.
That's by design, and helps make the case for MOAR FREEWAY$$!
https://en.wikipedia.org/wiki/Induced_demand
That photo looks like the 26-lane wide Katy Freeway in Houston! I use the rule of thumb of 2000 pphpd (passengers per hour in peak direction) for a fully-loaded freeway lane from this much better-looking graphic we saw last time we discussed this question on lemmy. (Apparently this graphic is now the headliner on the pphpd wiki page!)
2000 pphpd per lane matches my own attempts to verify this value. I couldn't find traffic stats for Katy Freeway, but here are the stats for Manhattan river crossings: https://www.nyc.gov/html/dot/downloads/pdf/manhattan-river-crossings-2016.pdf Specifically, the George Washington Bridge is a very busy bridge with 7 lanes in each direction and highly-optimized traffic density - constant traffic flow with no spacing in between - a good example of peak highway lane capacity IMO. It moves 290k vehicles per day, but more importantly 11k incoming vehicles during peak morning rush hour (page 10), which is 1600 vehicles per lane. The average occupancy is 1.74 (page 24, though not sure how that treats buses), so that's 2800 ppphd per lane.
GWB does have a lot of truck traffic though. The Holland Tunnel has 2 lanes in each direction, no trucks, constant traffic flow with no spacing, 2700 inbound vehicles during peak morning rush hour (page 10), and 1.22 occupancy (page 24), resulting in 1600 pphpd per lane.
So that's
2739*1.22 + 4860*1.41 + 11474*1.74= 30k people crossing from New Jersey into Manhattan during the morning rush hour using the 2+4+7=12 lanes of the Holland+Lincoln tunnels and GWB or 2500 pphpd per lane. I believe that sufficiently approximates 13 lanes of Katy Freeway, which has no trucks and no buses.Compare that to the 22k people transported from New Jersey into Manhattan during morning peak rush hour by PATH trains in two incoming tubes (https://www.panynj.gov/content/dam/path/about/statistics/2023-PATH-Hourly-Ridership-Report.pdf page 14, only shows turnstyle entries but almost everyone entering is travelling to Manhattan). And PATH trains look outright empty compared to crowd crush on NYC trains. Lexington Avenue Subway is like 32k pphpd for a single express track (https://new.mta.info/document/22126 page 5B-4,
25*1296in 2002 and has gone higher since).In conclusion, the numbers in this meme photo do not reflect full capacity, thus leading to questions and confusion, but the overall comparison is still valid: one half of a 26 lane highway has about the same capacity of ~30k pphpd for peak hour travel as one half of a 2-track railway.
when r u gonna build a traintrack outside my house plz and thank u
if u dont build a traintrack to every single house itd be a waste of time due to current scales of infrastructure.
At 25mph, the safe distance between cars is closer to 60-70 feet. Add the length of the cars for another 15-20 feet and your throughput calculations drop by a factor of 2.5-3 already.
It gets worse once you start considering comparable velocities. Trains go way over 25mph.
Also assume that no one is turning onto or off of the road?
Theoretically the highway I can see outside my window could handle tens of thousands of passengers per hour moving at over 60mph. But for some odd reason when I look out my window on workday it's moving significantly less than 25 mph. Some days is not even moving at all.
Yeah but for long term growth is not ideal, the tracks will do a better job in long run.
No matter the math, trains move more people, faster and safely. What you should use for your argument is that it's easier and better to low capacity roads in rural areas (low population) than building trains to replace the car everywhere. Either way there is no argument against trains from city to city or a metro. Cars get out competed there.
I don’t disagree, but we shouldn’t be pulling numbers out of our asses that are orders of magnitude different from the real figures.
Quick search gave this number:
So the bottom would probably be more like 25K each way. Lightrail is only about 4-8k? Meanwhile a single subway lane each way could do more than that thing on the bottom left.
I'm guessing you found this source: https://www.mikeontraffic.com/numbers-every-traffic-engineer-should-know/
The number from that page he should actually be using is more like this one:
(Source: I'm a former traffic engineer.)
Yup.
What does "should" mean in this context? Wouldn't it depend on if you are trying to compare peak capacities or daily usages? I'd assume which one matters more would vary based on why you are comparing them in the first place?