Park and ride lot geometry

Elements of Access: Transport Planning for Engineers, Transport Engineering for Planners. By David M. Levinson, Wes Marshall, Kay Axhausen.
Elements of Access: Transport Planning for Engineers, Transport Engineering for Planners. By David M. Levinson, Wes Marshall, Kay Axhausen.

I don’t find park and ride lots attractive. I don’t want them in my neighborhood. I wish the land around park and ride lots were valuable. But let’s do some math.

In one acre, there are 43,560 square feet. It takes about 300 square feet to store a parked car (including lanes, etc.). This suggests you can store 145 parked cars per acre. That is similar to this result.

If every one of those parked cars carried 1 person, that is 145 transit boardings from that station in the morning (and 145 boardings elsewhere in the evening, assuming symmetry). That generates 290 daily transit trips.

In contrast, let’s say we had zero park and ride spaces. Let’s further assume that adjacent land uses have a 50% transit mode share for work trips and 0% for non-work trips. We would need 300 resident workers on that acre to have a similar number of transit trips generated. Since only half the population works, we are looking at 600 total persons on that acre of land. That is the equivalent of 384,000 persons per square mile. That is a lot of people.

Even if only workers lived there, and they had 100% transit mode share for work trips and another 2 non-work trips per day by transit, that is still 145 people per acre. That is the equivalent of 92,800 people per square mile. That is Manhattan like densities (actually higher). Of course not all of Manhattan is high-rise apartments, so that is not necessarily as high as the highest densities in Manhattan, but it is higher than the lowest densities in Manhattan.

Low, or even medium, density land use around the station will not enable as many transit users  as the park and ride lot.

I still don’t like park and ride lots.

Jarrett Walker has a different take

13 thoughts on “Park and ride lot geometry

  1. This choice is not made in a vacuum. Things depend on circumstances.

    If you start with lots of downtown parking lots, you get choices between (a) a parking lot downtown plus an apartment building at a suburban rail station, or (b) an apartment building on a former parking lot downtown plus a park-and-ride lot for downtown workers who lose parking. (b) is clearly the better choice (and Jarrett Walker agrees).

    On the other hand, suppose you replace a portion of a rail line’s parking spaces with buildings, and raise the price of parking on the rest. Some of those who previously parked will now take the bus to the rail line. And using the new revenue from parking fees & ground rent to improve frequency or span of service on the transit will help ridership.

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  2. Land use at each station affects the value of travel from every other station as well. No one takes the train TO a P&R (unless there are perhaps rentable cars stored there — not a bad idea, hmmm…), but people may take the train to a station where there are residences and businesses. If you look at total system ridership rather than individual station hoardings, this additional use could provide the “missing” trips in your analysis.

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  3. You are only considering a very limited number of trip purposes (and travel options). Put mixed use with offices, services and entertainment at the location and you will have trips being made to and from the location at all times of day. It is more than just the physical attributes of a destination which create an activity hub.

    This is basically the “Vancouver” tower and pedestal development model, where a few towers (both condo and office) sit on top of a mini-mall base which includes health-care and daycare clinics, government offices, retail, entertainment, and eating options, and more…. Such sites can generate a few *thousand* public transport trips per day, with very limited parking.

    In order for public transport to be viable, it must be used for more than just the peak periods. Furthermore, activity hubs are far more suitable for integrating with active transport and shared modes.


  4. According to a list I compiled in my spare time, the average building built in downtown Minneapolis this decade has had 208 units per acre. Around the University and in Uptown that average is about 100 units per acre. This is, of course, gross density, but considering residential units typically house 1.5 to 2 people, I’m not sure the working residents per acre you require to beat park and rides is all that unrealistic for transit station areas.


  5. My point is basically applying to suburban park and ride lots that people want to convert to relatively low density new urbanist style development. If you can get Vancouver (or even downtown Minneapolis) style development, go for it. I don’t think that is the case at most suburban transit stops and stations in the Twin Cities region.


  6. I think you need to describe the area of the p’n’r. A park/ride 20 miles out in the bedroom suburbs served by a commuter train is a much different thing than a light rail station 7 miles out that’s in an inner-ring (say) suburb.

    In the former, you’d be lucky to get trips *to* a dense development pretty much whatever you did. Part of that is geography and part is how commuter trains are run (mostly peak flow, hourly service all day if you are really lucky)

    In the latter, everything said here is probably true, but again, part of that is geography and part is how light rail systems are run (lots of service both ways all day, more at peaks).

    Maybe my argument is for more service on commuter train lines. 🙂

    Anyway, as someone said, you can’t look at this in a vacuum. In an area with lots of density already (compared to the zero density of a p’n’r at least) you probably won’t get a p’n’r because of land costs. And in an area that doesn’t have the density, you probably *will* get one because the land is cheap .. because there is no density … and so people really do need to be delivered to the station in private automobiles.

    Where are the in-between cases?


  7. This math would imply that all Green and Blue line stations should be surrounded by park and rides. This is obviously wrong/not preferred. One quick check of this is boarding data from Metro Transit. For Fall 2013, average weekday boarding at the 38th Street Station was 1,600. Some of this is from transfers (which wouldn’t apply nearly as well in the ‘burbs), but how much? 2010 TBI data says that 63% of Blue Line riders did not transfer from another mode. That’s still over 1,000 boardings on the average weekday. That’s still triple what you have estimated a full park-and-ride lot would provide.

    Obviously an LRT station (or good bus station/stop) doesn’t have to rely on one acre, but instead on the potential walkshed surrounding it. According to the 2010 Census, the one half mile radius around the 38th Street Station contained 7,219 people. If half that population works, that’s 3,600 people, or SIX times more people than you estimated would need to be at the park and ride location to make up equivalent ridership.

    Note that the area around the 38th Street Station isn’t that dense. The walkshed is about 620 acres for a density of 11.5 people per acre (roughly 5 units/acre). So the choice suburban areas have is not necessarily between Vancouver-like densities and park and rides, it’s a choice between park and rides and and 5-10 units per acre. Transit agencies impact this choice by owning, operating and subsidizing park and rides.


  8. You’re also assuming that the ridership from the area outside that one acre is independent of whether it’s used as a P&R or housing. The immediate station area can have an effect on the attractiveness of walking to the station and can increase transit ridership by itself. Having a place to get coffee on your way to work, for example, can be a big benefit, while having to walk across a parking lot and then on streets flooded with P&R traffic can be a detriment to the attractiveness of the transit service. So if you build housing, you have the ridership from the housing, plus you have increased walk-up ridership, and while you lose the P&R ridership, some of those may in fact switch to walking, especially if the P&R was was free.


  9. So 620 acres develop 1000 rides. No problem, I am not suggesting a 620 acre park and ride lot could be filled. But that does not mean a 0 acre park and ride lot is necessarily the answer either. The marginal number of additional riders from that 1 acre is larger in most cases (suburban P&R, most of which are express bus P&R, not LRT) with parking than with development. This is why transit agencies do build P&R lots. Clearly this Return on Parking in terms of the number of rides diminishes with size of parking lots, otherwise parking lots would in fact pave the world.


    1. Understood, and I get your point. In our metro, the regional planning agency has transit planning AND land use authority. P&R decisions are also not made in a 1-acre vacuum. New P&Rs have recently been built in Lakeville, for example, surrounded by a corn field. What density is required by the regional planning agencies around this station? Transit-supportive, or P&R lock-in? Also, I’d be interested in a larger analysis of why we build P&Rs in the first place. Can we wait until 5-10 u/acre arrives to serve areas that would otherwise be very expensive to serve with transit?


  10. I suspect an acre-sized parking lot would need more space than the 30 square meters per space standard figure, for efficient access.

    But yes, in efficient land use, it’s not clear that parking lots or garages for people to drive in is always inferior to local dense development.

    What is clear to me is that the park-n-ride shouldn’t be free or subsidized. TOD renters would be paying market price; so should the parkers. If drivers outbid development use, fine, but let them pay.

    Say a space costs 30 m2. A 2BR apartment might be 60-90 m2. So a parker should be paying a third to half of what a renter would pay for a near-transit apartment. Okay, less, because it’s cheaper to build and maintain a parking space than an apartment. But still, way more than the $2/day of BART lots.


  11. You seem to be assuming that none of the PnR riders would continue to ride the train if the parking lot was developed. I’m sure you would lose some percentage, but assuming 100% loss makes no sense at all.

    Furthermore, you don’t consider the financial implications of the land use itself. If the lot is on transit agency owned land, the funds from development will go back into the system in ways that could easily up ridership by more than that loss from the lost parking spaces. Even for outside owned land, I would presume that the transit agency is then leasing the land which has a cost, etc.


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