The National Academies

Transit IDEA J-04/IDEA 61 [Completed (IDEA)]

Flexible Carpooling to Transit Stations
[ TCRP J-04 (Innovations Deserving Exploratory Analysis--The Transit IDEA Program) ]

  Project Data
Staff Responsibility: Jon M. Williams
Research Agency: Trip Convergence
Principal Investigator: Paul Minett
Completion Date: 8/12/2013

This project investigated and defined a flexible carpooling service to increase the amount of carpooling to transit stations, and designed a field operating trial to test the concept.

Many transit station parking facilities are full to overflowing. Parking at transit stations often has a high capital cost and limited opportunity for expansion. Arriving commuters using the parking facilities are generally driving alone. Transit ridership could be increased, and the effectiveness of investments in parking at transit stations improved, if mechanisms could be developed that encourage more people to carpool to transit stations.

Flexible carpooling is a system in which morning carpools are formed at designated residential-end meeting-places to travel to designated high-volume destinations. Flexible carpooling is characterized by an absence of the trip-by-trip pre-arrangement found in other carpool formation systems, relying instead on sufficient people arriving at the meeting-place seeking rides (and lining up) and sufficient drivers arriving seeking riders. The person at the front of the line gets into the car at the front of the line. Evening carpools are formed in a similar way at designated work-end meeting-places, although morning riders could also take other modal options to return to the morning meeting-place or other evening destination.

This project studied the use of flexible carpooling to get more people to transit stations.

 A literature search was conducted and a compendium compiled of existing knowledge about flexible carpooling. Notably it was found that a flexible carpooling route has never been sustainably implemented as a project. In the absence of previous projects to implement flexible carpooling, the design of a service and field operating trial would therefore have to include mechanisms to catalyze the start of a new route.

To find an appropriate route to evaluate, five popular Seattle-area transit station parking facilities were selected and their usage analyzed. A number of potential routes were identified and one, Bonney Lake to Sumner Station, was chosen as the target for design of the field operating trial.

Sumner, WA, is a small town 33 miles south of Seattle. Sound Transit operates the Sounder commuter rail service through Sumner, northwards to Seattle and southwest/northwest to Tacoma, and points in between. Sumner Station has a parking facility for Sounder passengers who arrive at the station by car. The parking facility has 286 spaces in a paved lot, and an adjacent 41-space unpaved lot, for a total of 327 spaces.

The parking at Sumner Station is ‘over capacity’ as demand exceeds supply, with all 327 spaces usually full by 6:15 am on week-days even though there are six subsequent commuter train services each morning (four northbound that arrive in Seattle before 9 am, and two Tacoma-bound that arrive in Tacoma before 8 am). Sound Transit is considering options for expanding the parking capacity at Sumner Station.

The origin address was identified for every vehicle using the parking at Sumner Station each day for a week. While the full Sumner Station catchment covers a large area, a concentration of users was found originating from the vicinity of Bonney Lake.
Each day about 100 vehicles from the Bonney Lake Catchment were found parked at Sumner Station. Across a week almost 200 unique vehicles from the Bonney Lake Catchment were seen at Sumner Station, a different grouping of 100 vehicles each day. There are very sound reasons to expect that there is unmet demand for parking at Sumner Station by people who live in the Bonney Lake Catchment.

Very near to the point on the escarpment where the traffic converges on the SR 410 highway, five miles from Sumner Station, there is a bus-station park-and-ride (PNR) with 356 spaces: the Bonney Lake South (SR 410) PNR. The Bonney Lake South PNR has well over 100 empty parking spaces every day.

Every vehicle from the Bonney Lake Catchment found parked at Sumner Station would have driven past the Bonney Lake South PNR on the way to Sumner Station. The opportunity identified by this project is for those commuters to stop at the Bonney Lake South PNR and use flexible carpooling for the remainder of their journey to Sumner Station, thereby reducing demand for parking at Sumner Station and delivering ancillary benefits.

A flexible carpooling field operating trial was been designed to take advantage of this opportunity. In return for parking at Bonney Lake South PNR and flexible carpooling to Sumner Station, it is proposed that flexible carpools be offered guaranteed parking (assigned dynamically as carpools are formed and communicated to each carpool) at Sumner Station plus other incentives. 50 Sumner Station parking spaces would be set aside for arriving flexible carpool vehicles from the Bonney Lake Catchment. 100 spaces at Bonney Lake South PNR would be dedicated to the system.

If fully utilized this would reduce demand at Sumner Station by 50 spaces per day, and increase Sounder ridership by 100 people per day. It would be the equivalent of adding 100 parking spaces at the Sumner Station without incurring the estimated $3 million capital and $60,000 annual operating costs associated with such an expansion.

The contractor's final report is available.

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