How much is the average car/bus parked?

January 27, 2012 8:38 AM

How much is the average car/bus parked?

I heard a snippet factoid that cars are parked 98% of the time, with 2% of the time spent actually driving. Does anyone have a concrete source for this? While we're on this topic, does anyone how much time buses spend parked? It's obviously a lot more than 2%, but what?

posted by bouchacha to travel & transportation (11 answers total)

When I get home, I can help - I think it's in the book The High Cost of Free Parking.
posted by Pants! at 8:48 AM on January 27, 2012 [1 favorite]

Google books search found "Cars spend about 95 percent of their time parked." in Traffic: why we drive the way we do (and what it says about us) By Tom Vanderbilt, p.148, with a cite to p.6 of Donald Shoup's The High Cost of Free Parking. A recent magazine article that discusses Shoup's work is here.
posted by Mr.Know-it-some at 8:54 AM on January 27, 2012

This table has average miles per vehicle at 12,000 in 2006. I couldn't quickly find any average speed data but that almost certainly means the average driving time for a vehicle is a single-digit percentage of total time in a year, unless people are averaging 13 mph or something.
posted by ghharr at 8:56 AM on January 27, 2012

On the car side, the average commute in the US is roughly 25 minutes. That's 50 minutes of driving per day, or 250 minutes per week. That's 2.5% of the 10,080 minutes in the week and doesn't include any errands or weekend driving.

On the other hand, there are certainly plenty of cars that are not used for commuting (cars owned by people who commute via public transportation, second cars, cars used by students and stay-at-home parents and retirees, etc.), so I can see how that would bring the average minutes-in-use per car down. It certainly feels right that the number is <5%, which really is pretty incredible.
posted by argonauta at 9:00 AM on January 27, 2012

With a quck check of my friendly neighbourhood Winnipeg transit site, I found they listed a fleet of 535 buses, but didn't list how many are active at any given time. Maybe another city's transit system will be more upfront with that info. If you were really committed to the analysis, it would be possible to get a lot from the posted route schedules.
posted by RobotHero at 9:09 AM on January 27, 2012

The Bureau of Transportation Statistics puts the number of passenger car registrations for 2009 at 193,979,654, and the vehicle-miles driven at 2,013,436,000,000. This averages out to about 10,400 miles per year per car.

As ghharr notes above, you'd then need an average speed to translate this into a time percentage. If the average speed is 30 mph, it works out to 4% of the year. At 50 mph, it's closer to 2.5%. At 20 mph, the car would be in use 6% of the time.

If you really wanted to nail this down further, you might be able to use the roadway vehicle-miles travelled figures, which break down the vehicle-miles travelled by type of road. Assign an average speed to each type of road and you'd be able to more accurately nail down the time usage. But that would be somewhat more involved; if you're just looking for a ballpark estimate, it's probably somewhere in the 2%-6% range.
posted by Johnny Assay at 9:10 AM on January 27, 2012

Oh, and using the same statistics, the average bus travels about 17,000 miles per year.
posted by Johnny Assay at 9:16 AM on January 27, 2012

Johnny Assay, I got 36,073 miles per bus (2,285,000,000 miles / 63,343 buses). That fits better with my perception, although it sounds quite low.
posted by ambrosen at 9:36 AM on January 27, 2012

For buses, your statistical hotspot is the American Public Transportation Association (APTA) Factbook; my calculations are based on appendix 2, which provides by urban area and by operator.

Nationwide, there are 63874 buses (motor bus and trolley bus) available for service, providing 159 million hours of revenue service, which is 28.4% of the potential max (all buses going 24/7/365). However, "revenue service" does not include what is called "deadheading", travel to and from garages, or between routes (say a bus does a suburb-to-downtown run from 6 to 9 AM, then goes to travel between a hospital and a mall for the midday; there is some time in between while the bus goes from downtown to the hospital). It also doesn't include reverse travel on an express commuter route, where in the morning the bus transports people from a suburb to the downtown, but won't take them back, then does the same in the evening. It also doesn't include time when buses are being cleaned, fueled and maintained in the garage.

Revenue service does include layovers and headway recovery; this is when the bus waits for a short period of time, occasionally to give the driver a break, but mostly so that it is on schedule. If a route takes, say, 51 minutes to drive, the agency will schedule it to take 60; it's better for scheduling connections and for riders, and if the bus misses a light or something, it won't be late.

There are also more buses available for service than actually providing service; to pick a city at random, Chicago's CTA has 2077 buses available, but only operates 1737 at maximum service. This covers buses being repaired, and spares, so if a bus or train breaks down, replacement vehicles can be in service quickly without screwing everything up. I used the larger total bus number.

This 28.4% figure doesn't include demand responsive transit ("dial-a-ride" or the like), which is lower - travelling 16.8% of the time. While I'm at it, light rail and heavy rail are providing revenue service 32.6% of the time, and commuter rail 17.0%.

Bus revenue service percentage by urban area size:
50-100K: 21.3%
100-250K: 24.5%
250-500K: 26.0%
500K-1M: 26.7%
1-3M: 29.0%
3M+: 29.9%

For major urban areas:
Atlanta, GA 33.4%
Boston, MA-NH-RI 28.4%
Chicago, IL-IN 34.4%
Dallas-Fort Worth-Arlington, TX 33.5%
Detroit, MI 25.8%
Houston, TX 26.2%
Los Angeles-Long Beach-Santa Ana, CA 30.9%
Miami, FL 34.7%
New York-Newark, NY-NJ-CT 28.2%
Philadelphia, PA-NJ-DE-MD 30.8%
San Francisco-Oakland, CA 31.5%
Washington, DC-VA-MD 27.0%

Note that this value varies from operator to operator in these urban areas. So in San Francisco, MUNI which operates in the city and has a lot of night service runs 41.7% of the time, AC Transit in the East Bay runs 33.5% of the time, and SamTrans and Golden Gate which are more suburban agencies with high commuter flows run 21.3% and 16.1% of the time respectively. The busiest operator in America is the Scottsdale Trolley, whose 15 buses are in service 62% of the time. The busiest major operator is Bi-State Metro in St. Louis, 57.4% of the time. Only one agency has its' buses running less than 5% of the time, KU in Lawrence, Kansas; but I believe it's mostly a fleet of shuttle buses used for parking lots during athletic events, so it doesn't really count.

The estimates of cars driving less than 5% are roughly correct; my back of the envelope guess is 4%. (So buses are travelling 6 or 7 times more than cars are.) The best source of data is the National Household Travel Survey, but I don't have time to play with that right now.
posted by Homeboy Trouble at 10:06 AM on January 27, 2012 [5 favorites]

Johnny Assay, I got 36,073 miles per bus (2,285,000,000 miles / 63,343 buses). That fits better with my perception, although it sounds quite low.

I was going by the "bus" figures included under the "Highway, total" category rather than the "Transit" category. I think the latter is included in the former (see Footnote "e" in Table 1-35.) However, if we're restricting ourselves to public bus service rather than school buses or long-distance motor coaches, then your numbers (and, on previous, those of Homeboy Trouble) are what we want.
posted by Johnny Assay at 10:11 AM on January 27, 2012

However, if we're restricting ourselves to public bus service rather than school buses or long-distance motor coaches,

Good point. For sure, school buses are travelling less of the time than public transit buses; I'd guess 10-15%, in line with commuter-oriented transit services. Intercity buses, I'm less sure about. Probably in the 25-35% range at least; there are more overnight and weekend intercity services.
posted by Homeboy Trouble at 10:33 AM on January 27, 2012