Thursday, April 12, 2012

Parking, Ridership and Greenbush

I noticed something in the MBTA's Draft CIP:
Over 3,000 new parking spaces have been built on stations along the new Greenbush commuter rail line.
That number seemed familiar, so I went back to check the Blue Book. There's only approximately 3,000 inbound riders per weekday on the Greenbush line, a fairly pitiful quantity. Is it a correlation that the number of parking spaces is almost equivalent, or just a coincidence? I decided to look at some numbers from the website.



StationParking SpacesInbound Riders
Nantasket Junction 495 367
Weymouth Landing/East Braintree 290 386
Cohasset 410 391
West Hingham 214 410
East Weymouth 335 420
North Scituate 279 532
Greenbush 1000 575


Both columns add up to approximately 3,000 but they get there in different ways. Parking spaces are clearly concentrated in Nantasket, Cohasset and Greenbush. But ridership seems almost evenly distributed, and not really dependent on parking. Kind of strange, really. I decided to scrape the rest of the numbers and see if there were any system-wide patterns.

I excluded stations that were also subway stations, because their users are overwhelmingly rapid transit riders. There's a lot of scattered points on this chart, though they form a little bit of an upward trend. The slope is ~0.84 riders per parking space constructed. There's a bunch of complicating factors to this picture: some stations are in densely populated areas, some are not; some have good local bus connections, others have nothing; some may have private lots serving them. It's hard to say whether the parking lots are driving ridership, or whether ridership is motivating the MBTA to build more parking. Stations such as Kingston, Greenbush, and Nantasket Junction report 70-80% average availability on their parking lots. Gloucester reports 77% availability on its 100 spots, but has ridership over 450. Actually, the whole Newburyport/Rockport line does pretty well in this respect. The two points in the upper-left of the chart are Salem and Beverly Depot, both with high ridership despite small parking lots. The largest parking lot is at Anderson/Woburn Station, with an average weekday utilization of 60% and an above-average number of riders.
Broken down by line, it's clear that there's some appreciable differences between them when it comes to parking and ridership. Greenbush has the smallest-slope line at 0.17, so perhaps there is something unusual going on there, after all. The Providence Line (1.38) has a great deal of parking (counting Providence itself, which also serves as an Amtrak station), and a great deal of ridership, so it comes out on top. It seems that local considerations play a large part in this story, and it seems that I may have to try and come up with numbers for the regional transit systems before I can put anything else together.

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