Virginia DOT

A new study finds that people who used to make the whole trip by bike or transit now drive to the station.

On paper, park-and-ride facilities seem like the ultimate transport compromise. Free or cheap parking near transit stations should, if the theory holds, make partial transit riders of metro area residents who used to drive the whole way into work. The system acts like a nicotine gum for daily commutes — weaning people slowly off the single-occupancy car.

In reality, some transport experts wonder whether park-and-ride does more harm than good. A study of park-and-ride facilities from the early 1990s found they don't necessarily ease congestion because they unleash latent demand for road space. Other research has come out similarly skeptical that park-and-ride reduces car use, though much of it has centered on bus-based transit.

A new study of park-and-ride at rail-based transit stations doesn't offer much in the way of encouragement. In an upcoming issue of the Journal of Transport Geography, Dutch researcher Giuliano Mingardo reports that park-and-ride facilities in two major metro areas create four measurable "unintended effects" that not only limit the benefits of transit but may even increase vehicle travel in the metro area.

Mingardo surveyed more than 700 travelers at nine rail-based park-and-rides around the Rotterdam and The Hague a couple years back — ranging in size from 15 parking spaces to 730. His questionnaires, given to people at afternoon rush, focused on what riders would do in the absence of the park-and-ride facility. Mingardo also conducted concurrent field observations of various stations.

Across both metro areas he found evidence for four unintended effects of park-and-ride facilities — two of which (asterisked) had never been documented:

  • Abstraction from transit. People who had once made the entire commute by transit now drove to the transit station.
  • *Abstraction from bike. People who had once made some or all of the commute on their bicycle now drove to the station.
  • Trip generation. People made more trips in general because the overall cost of transportation was lower.
  • *Park and walk. People parked at the station but walked somewhere nearby and didn't use transit at all — potentially displacing transit riders and disrupting the area parking market.

In Rotterdam, Mingardo found that only about a quarter of park-and-ride users said they would use a car for their entire commute in the absence of the facility — which is the desired effect. The rest fell into one of the above categories. As a result, Mingardo calculates that there's a net addition of 1,272 vehicle kilometers traveled, as well as an increase in carbon emissions.

The situation wasn't universally flawed. "Remote" stations — meaning park-and-ride facilities deep into the suburbs that captured city commuters early into the trip — performed well. And in The Hague, Mingardo did find a slight net reduction in vehicle travel and emissions. Still, even there, the presence of unintended effects seemed to mute most benefits of park-and-ride.

Generally speaking, in accordance with previous research, he believes that park-and-ride facilities "do present a net increase in traffic volume rather than a reduction":

Indeed, the number of car-km saved from the P&R site to the inner city is usually more than compensated by the increase in car-km travelled to reach the P&R site by those users who switched from public transport services and bikes, those that were previously not travelling and (possibly) the Park and walk users.

Despite the findings, the takeaway here is not necessarily that park-and-ride doesn't work. These facilities should certainly be monitored by cities to make sure they're meeting policy goals — especially if that goal is traffic reduction. Additionally, it seems clear that suburban or "remote" park-and-rides fulfill more of that goal than those closer to the city center.

Mingardo's research also found that many travelers were willing to pay a bit more for parking, a sign that some of the unintended effects might be mitigated with proper pricing. The logical conclusion here is that cities should impose parking fees large enough to remove the incentives of free parking but not so large that people drive all the way into work. That might not ease congestion in park-and-ride corridors the way some had hoped, but it would certainly get a lot closer to a true transport compromise.

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