Having the commit will make it maore feasible to fund vehicles that are intended for a specific area, and the pool model allows Uber to recover margin during pricing surges and users who don't want to pay the commit (after all, the discount on the fare would only apply to the portion of the pool fare ascribed to the subscribed to the passenger).
EDIT: Punctuation
Running empty high capacity vehicles over a really large number of routes is immensely wasteful, much more wasteful than on-demand vehicles.
One thing much of this analysis is missing is how much more in demand commuter vans will be. Transportation will be much more hub based for both long and very short trips. A middle of the range option will fill the void, which is large. Given much of transit is pre planned with times and locations, for jobs, van use in self driving cars will be enormous.
Edit: It should be noted this was in the context of a discussion regarding ad-hoc pairing systems for carpooling/ride-sharing possibly making car travel much more efficient, possibly with vehicles that seat more (minivans, full size vans, small busses).
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I actually wonder about this. Is it a matter of most cars being mostly empty, or is it inherently impossible to match the mass transit capacity. If we look at it as passengers carried over space required and time spent, here's how I see it:
Rail mass transit does not as efficiently use the land it's on a occupancy basis (there's not always a train on a specific square foot of track). In peak times, cars are more efficient on a vehicle basis. According to BART system facts[1], there are 107 miles of track. There are 669 cars, seating for 72 in 448 of them with each being 70 feet (with 59 of them having an additional 5 feet for a cab), and seating for 64 in 230 cars[2] (with an indeterminate car length, so I'll use the smaller listed), for a total capacity of 46,976 seated people. BART states that all cars can hold over 200 people in a "crush" load, so we'll assume 200 as the theoretical maximum, and say BART can carry 133,000 people when at peak (crush) capacity, and over the 107 miles of track, that gives us a density of 1,250 people per linear track mile, but with only 8.3% track utilization at any one time.
Cars do not as efficiently pack people per vehicle usually, but can more efficiently use the roads on a per-vehicle basis. Assuming very heavy traffic which is not stop-and-go, so perhaps 35 miles an hour average (the same as BART), and a 4-lane highway (two each direction), if each car is allowing two car lengths between itself and the car in front (slow traffic), we have approximately 33% road utilization (or 25%, or 20% depending on what you think the average space between vehicles is). Since carpooling seems to be at about 10% currently carpooling[4] (ignoring that it may be different in certain arterial routes, as we are discussing), we have around 1.066 people per car[5] as a lower bound. With an average car length of 177.2 inches[6], or 14.77 feet, we can estimate the people per mile on the highway during this time as being 604 people per mile of 4-lane highway.
Interesting take-aways for me:
While 4-lane highways may take more room than rail (not sure the actual sizes here), they are also more versatile.
If the highway bogs down below 35 mph, it's then less than the average rate of BART, and we need to start computing people over time instead of just people over distance.
BART has much more room to increase track utilization, but there is likely unaccounted for overhead here on each train. Optimal usage at current speed is one train arriving immediately after the prior one leaving, at 35 mph exact speed and 20 second stops, for a train of six cars (?) and 425 feet, that would be cars 2.42 train lengths apart, and a utilization of 29%, or roughly a 4x increase over current rates, 5,000 people per track-mile.
Cars have much more room to increase vehicle utilization. If we replaced 50% of vehicles with full size vans transporting on average 7 people each and didn't touch road utilization, we would be at an overall average of 4 people per car, and 2600 people per highway mile. Interestingly, if we somehow moved towards a system where smaller vehicles picked up and shuttled people with small amounts of sharing to bus-stations where they were sorted into smaller buses (40 people) going specific area depots, and from those depots dispersed again to final destinations using individual cars with small amounts of sharing, we might easily surpass rail transit systems. averaging 20.5 people per vehicle, but with somewhat more area used should put us close to 10,000 people per highway mile.
Of course, there's a lot of assumptions in all the numbers, and some speculation in the possibilities, but I thought it was interesting to figure out. ;)
1: http://www.bart.gov/about/history/facts
2: I know the total car numbers don't add up. Complain to BART, it's their data.
3: (66970 feet + 695 feet)/(7 * miles * 5280 feet/mile) = (47125 feet)/(564960 feet) = 8.3%
4: https://www.census.gov/prod/2011pubs/acs-15.pdf, table 1.
5: 105,476 drove alone, 13,917 carpooled, if we assume all carpooling was just two people per car, we get person to car density by (105,476+13,917/2)/105,476 = 1.066 people per car
6: https://www.reference.com/vehicles/average-length-car-2e8538....
7: 5280 feet/mile / 14.77 feet/car * 0.33 highway mile utilization = 117 cars at highway lane mile utilization. 117 cars * 1.066 people/car = 126 people per mile of highway lane. 4 lanes fives us 604 people per highway.
(numbers unrelated to yours)
1. BART track utilization at peak times is already pretty much at capacity. The typical westbound rush hour train will be waiting in the transbay tube for trains ahead of it to unload passengers at Embarcadero.
2. Seating capacity on BART is underreporting the ridership. At least 30 more people fit into each car during peak and late hours.
It's great that you dove into the napkin math and worked out your idea. I think that the notion of using many busses is worth looking into. When it comes to capital expenditure and ongoing subsidization, BART is an expensive remedy for traffic congestion.
I think the most vital part of the exercise is to examine the choke points: the Bay Bridge and Market St. Without another bridge and another level for road traffic, I don't see how the city could accommodate the extra usage from the loss of BART, van/bus use notwithstanding.
I was hoping people would chime in with actual experiences. I've lived an hour North of SF all my life, but have never ridden BART. There's little reason to if you already have to drive quite a distance just to get to a station, and you only visit the city occasionally.
> Seating capacity on BART is underreporting the ridership. At least 30 more people fit into each car during peak and late hours.
30 more people from the per-car numbers, or from the "crush" load they report, which is "over 200" (and I used 200 for my calculations).
> I don't see how the city could accommodate the extra usage from the loss of BART, van/bus use notwithstanding.
I wasn't really making a case for eliminating BART, but more for where future load capacity might come from. If we already have a mass transit system the numbers show it's a very efficient, if fairly rigid solution than we should keep that and expand it as much as feasible (which likely means, maximizing current tracks, not creating new ones).
That said, a lane packed with buses is much more dense with people than even BART, so dedicated bus lanes (10+ seat vehicles) combined with a shift to ad-hoc ride sharing might do it. Getting from here to there would be hard though.
