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Measuring Sound Transit Link Light Rail Reliability

35% of a sample of light rail trips took three minutes or more longer than the 37 minutes stated by the schedule. This is a higher percentage than last fall when 26% of trips were this far behind schedule.

The below field observations were made on a sample of 40 one-way trips on Central Link Light Rail from January 28 to March 26, 2010 between Westlake and SeaTac Airport, in one direction or the other. No trips taken by the observer within this date interval were excluded from the sample.

The scheduled travel time for these trips is 37 minutes.

Results of the survey:

The observed and measured trip time was no more than one minute slower than scheduled 27.5% of the time, 11 trips, indicated in the green rows below. Six of these trips were faster than the scheduled time. We call these 11 trips "on time."

37.5% of the trips, the light rail travel time was one to three minutes longer than scheduled -- 15 trips, indicated in yellow rows.

So 65% of our sample of Link trips were on time, or almost on time.

On 20% of the trips, travel time was three to six minutes longer than scheduled -- 8 trips, shown in orange rows.

And in another 15% of the trips, travel time was six to 14 minutes longer than scheduled -- 6 trips, shown in red below.

These results represent a slight deterioration from the result of a sample of runs taken last fall, when 35% of the trips were on time (instead of 27.5%), and 26% (instead of 35%) took three or more minutes longer than the schedule.
 

Date

Day of week

Departure time

Departure station

Arrival station

Actual trip time

Sscheduled trip time

Lateness

2-4

THU

2:48 PM

SeaTac Airport Airport

Westlake

34:50

37:00

Early

3-1

MON

2:51 PM

SeaTac Airport Airport

Westlake

35:45

37:00

Early

3-24

WED

6:13 PM

SeaTac Airport

Westlake

35:50

37:00

Early

2-5

FRI

9:18 AM

SeaTac Airport

Westlake

36:00

37:00

Early

3-1

MON

2:07 PM

Westlake

SeaTac Airport

36:40

37:00

Early

2-3

WED

11:48 AM

SeaTac Airport

Westlake

36:50

37:00

Early

2-11

THU

4:09 PM

Westlake

SeaTac Airport

37:20

37:00

0:20

2-9

TUE

6:33 PM

SeaTac Airport

Westlake

37:25

37:00

0:25

2-19

FRI

2:17 PM

Westlake

SeaTac Airport

37:25

37:00

0:25

3-9

TUE

1:17 PM

Westlake

SeaTac Airport

37:45

37:00

0:45

3-18

THU

12:57 PM

Westlake

SeaTac Airport

37:45

37:00

0:45

3-26

FRI

5:36 PM

SeaTac Airport

Westlake

38:10

37:00

1:10

2-5

FRI

8:26 AM

Westlake

SeaTac Airport

38:25

37:00

1:25

2-11

THU

4:51 PM

SeaTac Airport

Westlake

38:25

37:00

1:25

3-9

TUE

2:00 PM

SeaTac Airport

Westlake

38:25

37:00

1:25

3-16

TUE

4:05 PM

SeaTac Airport

Westlake

38:25

37:00

1:25

3-18

THU

1:40 PM

SeaTac Airport

Westlake

38:30

37:00

1:30

3-2

TUE

11:10 PM

SeaTac Airport

Westlake

38:40

37:00

1:40

3-16

TUE

3:22 PM

Westlake

SeaTac Airport

38:50

37:00

1:50

2-19

FRI

2:58 PM

SeaTac Airport

Westlake

39:00

37:00

2:00

3-12

FRI

5:12 PM

SeaTac Airport

Westlake

39:05

37:00

2:05

2-26

FRI

3:50 PM

SeaTac Airport

Westlake

39:15

37:00

2:15

2-4

THU

1:56 PM

Westlake

SeaTac Airport

39:25

37:00

2:25

2-13

SAT

5:06 PM

Westlake

SeaTac Airport

39:35

37:00

2:35

3-12

FRI

4:31 PM

Westlake

SeaTac Airport

39:45

37:00

2:45

2-8

MON

1:07 PM

Westlake

SeaTac Airport

39:55

37:00

2:55

3-26

FRI

4:52 PM

Westlake

SeaTac Airport

40:10

37:00

3:10

3-22

MON

7:52 PM

Westlake

SeaTac Airport

40:20

37:00

3:20

3-24

WED

5:30 PM

Westlake

SeaTac Airport

40:20

37:00

3:20

2-3

WED

10:54 AM

Westlake

SeaTac Airport

40:25

37:00

3:25

3-22

MON

8:40 PM

SeaTac Airport

Westlake

40:25

37:00

3:25

1-28

THU

5:50 PM

Westlake

SeaTac Airport

41:10

37:00

4:10

2-13

SAT

5:50 PM

SeaTac Airport

Westlake

42:20

37:00

5:20

2-8

MON

2:00 PM

SeaTac Airport

Westlake

42:45

37:00

5:45

2-9

TUE

5:36PM

Westlake

SeaTac Airport

43:40

37:00

6:40

2-1

MON

3:18 PM

Westlake

SeaTac Airport

44:15

37:00

7:15

2-26

FRI

2:57 PM

Westlake

SeaTac Airport

44:35

37:00

7:35

3-6

SAT

3:20 PM

SeaTac Airport

Westlake

47:45**

37:00

10:45**

3-2

TUE

10:09 PM

Westlake

SeaTac Airport

51:30*

37:00

14:30*

3-6

SAT

2:20 PM

Westlake

SeaTac Airport

52:00**

37:00

15:00**

Notes from the observer on the three longest delays in the red columns:

*Sound Transit was performing maintenance on the tracks between Rainier Beach and Tukwila after 10 pm, which was announced in rider alerts beforehand. Not all trips after 10 pm were delayed during the sampled interval.

**Work was being done on the highway overpass next to Stadium Station, and Link did not go north of SODO. This work was announced by Sound Transit before the trip.  All passengers had to use shuttle buses between Westlake and SODO, then transfer to Link.

                    Sound Transit has provided the following measurements of its own:

Headway performance is monitored against our advertised operating frequencies of every 7.5 minutes during peak hours and every 10 or 15 minutes at other hours. The average headway performance for the referenced three months shown below is 89%. In other words about 89% of the time Link passengers did not have to wait more than three additional minutes beyond the scheduled headways for their train. The monthly headway performance is noted below:

February 2010              90.23%
March 2010                  88.77%
April 2010                     87.12%

End to end performance is measured by considering the actual time trip time when measured against the scheduled trip time of 37 minutes.  Those figures are:

February 2010              92.8%
March 2010                  92.3%
April 2010                     93.0%

                    The average number of trips performed within the scheduled time for the referenced three months is 92.7%.

Click here for complete information from Sound Transit on riding Central Link Light Rail. The seated capacity of the trains is far from being used during most hours of the day, so now -- in the early days of operation -- is a good time to experience light rail.

There is often free parking at the Tukwila Station just north of SeaTac Airport on International Boulevard (SR 99); otherwise, the easiest access is via Metro Bus to downtown Seattle's Transit Tunnel.

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Last modified: February 07, 2011