How does the rain affect the work commute for people in the Seattle metropolitan area?

Research Project
Gabriel Hess
City University of Seattle
BC303 – Statistics
Greg Judge
June 1, 2012

How does the rain affect the work commute for people in the Seattle metropolitan area?
Table of Contents
Abstract, Objectives, and Sampling Methodology…………………………………3
Sample Demographics………………………………………………………...……4
Time of Day for Commute…………………………………………………………5
Commute Distance…………………………………………………………………7
Commute Method…………………………………………………………..………8
Length of Commute………………………………………………………...………8
Conclusion…………………………………………………………….…………..10
Original Objectives Reviewed…………………………………………………….11
If Unlimited Time and Resources…………………………………………………11
Survey Sample………………………………………………………………….…13
Summary of Responses……………………………………………………..…….15
References…………………………………………………………………..…….20

Abstract, Objectives, and Sampling Methodology
Does rain have a significant effect on Seattle area commuters? Seattle has always had a rumor attached to it as being the one of the nation’s rainiest cities. This is actually not the case at all. Ben Miller of Puget Sound Business Journal referred to a recent study, and said that “Mobile, Ala. was the nation's rainiest city. Seattle didn't even make the top 40” (Miller, 2007). It does however rain in small amounts on many days throughout the year, and this trend seems to affect the Seattle area commute in a derogative way. The challenge of getting to work and other appointments on time can be difficult enough when the sun is out, so rainy weather is an unwelcome added ambiguity in a commuter’s schedule.
A research survey was created with the objectives of showing whether or not rain affects freeways or side roads differently, if it hampers the commute on a Monday through Friday more so than others, and that there is a percentage of time that people should add to their allotted commute times when it is raining. The survey was made available only online, and the link to it was placed on Facebook, LinkedIn, and the Pierce County employee internal website. It is worth noting that there may be a slight bias to Pierce county workers because most of the results came from the link on that web page. The survey was closed when a sample size of 100 responses was received.
The following is a detailed report of the findings from this survey, a discussion of whether or not the original objectives were achieved, suggestions as to what should have been done if there was unlimited time and resources, a copy of the survey, and a summary of the 100 responses that were received. As will be shown below, the effects of rain on a commute here in the northwest are significant, and should be considered when planning a daily schedule.

Sample Demographics
The Age groups seemed to be fairly expected for the sampling with the exception of the 26-35 age group where there was a slight spike. This increase is most likely due to the age of those who saw the survey on the social networking sites, and made this age group the mode of the sample. If the median value of each age group is used in accordance with the frequency (60 assumed for the upper group), it can be assumed that the mean age would be 40.1 years.

The fact that approximately 70% of the responses came from the link on the Pierce County employee website means that there is a slight bias towards the south Puget Sound area over the central or north areas. This also led to a higher percentage of people working there but residing elsewhere.

Time of Day for Commute
Seattle is notorious for having bad traffic during rush hour. According to a study by NavTeq (2010), Seattle is the 4th worst city in the nation for rush hour traffic. For the purpose of finding the mean for commute times driving to/from work, the median time of each range was used with the exception of the “before 5am” and “after 9am” groups. Using this method the mean time for people driving to work is 7:03am, and the mean time for people driving home is 4:39pm. It is also interesting to note that there is a negative skewness on the graph below for the driving to work times, and a positive skewness on the graph for driving home times.

In most cases people assume a standard work week is Monday through Friday. However 20% of this sample group works an alternate schedule which could mean different days off or even a schedule that changes week to week.

Commute Distance
The extreme positive skewness of the graph below for commute distance would seem to indicate that perhaps the answer options for this survey question should have been smaller distances or even more intermittent choices. However, it does make sense that the mode for this question is those that travel less than 10 miles because it is logical for people to ultimately find work as close to home as possible. Using the median of each bottom four range groups and 50 for the upper range, the mean distance that people in this sample group travel to work is 16.9 miles.

Commute Method
The route that people take when commuting was surprisingly split down the middle between “mostly freeways” and “mostly side roads”. It is safe to assume for this sample that the results are not bias towards one commute route or the other.

Length of Commute
To determine the percentage of increased commute time when raining, the comparison should be between the mean commute times between the two scenarios. Using the median of each bottom four range groups and 75 minutes for the upper range, the mean commute time for people when not raining is 26.2 minutes, and when raining is 36.6 minutes. This shows that on average the people in this sample experience a 39.7% increase in their commute times when it is raining.

Comparing the charts above, one can easily determine that out of the same sample group of people, the commute times increase significantly when it is raining. The number of people that have a commute longer than 20 minutes is much greater on the rainy commute chart.

As shown in the graph above, the increase in commute time caused by rain can vary depending on schedule and commute route. On average the commute time for those working a Monday through Friday schedule increased 38.9% when raining as opposed to only 29.7% when working an alternate schedule. For those commuting on mostly freeways the average increase was 38.1%, while commuters using mostly side roads only increased 21.1% on average.
Conclusion
As shown in the details above, the daily commute is definitely affected by the rain. The important numbers to note are that for this sample group, on average the time people are commuting is around 7:00 am and 4:30 pm, 80% of them are working a Monday through Friday schedule with an average commute distance around 17 miles, the average commute time when not raining is 26 minutes, the average time when it is raining is 37 minutes, and the increase in commute times when raining is 40% on average. There was not a distinct difference in the amount drivers commuting on freeways or side roads, but the increase of time added when raining was nearly double for freeways as it was for side roads. The increase in commute time was also for those drivers working a Monday through Friday schedule than for those working an alternate schedule. Also of note for this sample group is that the average age was 40 years, and 77% of these workers were commuting to Pierce County for work. Perhaps if commuters assume their commute will increase 40% when it is raining, there will be many fewer “traffic” excuses when arriving to work or an after work appointment late.
Original Objectives Reviewed
The original objectives of determining whether or not rain affects freeways or side roads differently, if it hampers the commute on a Monday through Friday more so than others, and a percentage of time that people should add to their allotted commute times when it is raining were addressed in the Length of Commute section as well as in the Conclusion. Freeways are definitely affected more than side roads when raining. The assumption for this would be that because high speeds are more dangerous with wet roads, people tend to drive slower than normal on the freeways but not as often on the side roads. The commute when raining is more derogatively effected on a Monday through Friday schedule than an Alternate one. This is most likely due to the high volume of commuters during rush hour. Finally, using the data from this sample group, the average time people can add to their commute time when raining would be 40%.
If Unlimited Time and Resources… This research was done with a limited amount of time available, and it required no funding. However, if the same research could have been completed using unlimited resources, it would have been much more detailed and precise. The data could have been considered extremely reliable with a sample size in the thousands. If given the opportunity to carry out this same research project with unlimited resources, multiple employers (public and private) around the Seattle area would have been used to distribute the survey. A paid survey service would have been used to gather responses in order to get more than the 100 that this report was limited to. The time to collect data from the survey would have been increased to at least a month, or until the sample size reached 5,000 including at least 500 from each county around the Puget Sound. This sample size would have included at least 2000 responses from commuters using freeways and side roads. It would have also included at least 500 commuters that work an alternate work schedule. Once this data was collected, a high powered statistical computing software program such as The R Project would have been used to analyze and display the data in the most legible way possible. This data would have been incorporated into a detailed report, and then submitted to multiple corporations and media outlets in the area. The hope would be that they would make this information readily available to the public, and ease some of the rush hour traffic issues around Seattle when raining.

Survey Sample
1. What is your age group? 16-2526-3536-4546-55Above 55 |
2. What county do you live in? KingPierceSnohomish | Other (please specify) |
3. What county do you work in? KingPierceSnohomish | Other (please specify) |
4. What time do you drive to work? Before 5amBetween 5am & 6amBetween 6am & 7amBetween 7am & 8amBetween 8am & 9amAfter 9am |
5. What time do you drive home from work? Before 3pmBetween 3pm & 4pmBetween 4pm & 5pmBetween 5pm & 6pmBetween 6pm & 7pmAfter 7pm |
6. How many miles approximately do you commute each way for work? Less than 10Between 10 & 20Between 20 & 30Between 30 & 40More than 40 |
7. Do you work a Monday through Friday schedule? YesNo |
8. How long is your commute on an average day without rain? Less than 10 minutesBetween 10 & 20 minutesBetween 20 & 30 minutesBetween 30 & 40 minutesBetween 40 & 50 minutesBetween 50 & 60 minutesMore than an hour |
9. How long is your commute on a day that it is raining? Less than 10 minutesBetween 10 & 20 minutesBetween 20 & 30 minutesBetween 30 & 40 minutesBetween 40 & 50 minutesBetween 50 & 60 minutesMore than an hour |
10. What type of roads do you typically use for your commute? Mostly FreewaysMostly Side Roads |

Response Summary
100 Total Responses

1. What is your age group? | | Response
Percent | Response
Count | 16-25 | | 7.0% | 7 | 26-35 | | 36.0% | 36 | 36-45 | | 19.0% | 19 | 46-55 | | 25.0% | 25 | Above 55 | | 13.0% | 13 | | 2. What county do you live in? | | Response
Percent | Response
Count | King | | 17.0% | 17 | Pierce | | 63.0% | 63 | Snohomish | | 1.0% | 1 | Other (please specify)Thurston-10, Kitsap-8, Multnomah-1 | | 19.0% | 19 |

3. What county do you work in? | | Response
Percent | Response
Count | King | | 16.0% | 16 | Pierce | | 76.0% | 76 | Snohomish | | 1.0% | 1 | Other (please specify)Kitsap-5, Multnomah-1, Mason-1 | | 7.0% | 7 | | 4. What time do you drive to work? | | Response
Percent | Response
Count | Before 5am | | 3.0% | 3 | Between 5am & 6am | | 15.0% | 15 | Between 6am & 7am | | 27.0% | 27 | Between 7am & 8am | | 37.0% | 37 | Between 8am & 9am | | 15.0% | 15 | After 9am | | 5.0% | 5 |

| 5. What time do you drive home from work? | | Response
Percent | Response
Count | Before 3pm | | 4.0% | 4 | Between 3pm & 4pm | | 24.0% | 24 | Between 4pm & 5pm | | 39.0% | 39 | Between 5pm & 6pm | | 18.0% | 18 | Between 6pm & 7pm | | 10.0% | 10 | After 7pm | | 5.0% | 5 | | 6. How many miles approximately do you commute each way for work? | | Response
Percent | Response
Count | Less than 10 | | 36.0% | 36 | Between 10 & 20 | | 33.0% | 33 | Between 20 & 30 | | 16.0% | 16 | Between 30 & 40 | | 9.0% | 9 | More than 40 | | 6.0% | 6 |

| 7. Do you work a Monday through Friday schedule? | | Response
Percent | Response
Count | Yes | | 80% | 80 | No | | 20% | 20 | | 8. How long is your commute on an average day without rain? | | Response
Percent | Response
Count | Less than 10 minutes | | 15.0% | 15 | Between 10 & 20 minutes | | 28.0% | 28 | Between 20 & 30 minutes | | 23.0% | 23 | Between 30 & 40 minutes | | 14.0% | 14 | Between 40 & 50 minutes | | 14.0% | 14 | Between 50 & 60 minutes | | 4.0% | 4 | More than an hour | | 2.0% | 2 |

| 9. How long is your commute on a day that it is raining? | | Response
Percent | Response
Count | Less than 10 minutes | | 7.0% | 7 | Between 10 & 20 minutes | | 22.0% | 22 | Between 20 & 30 minutes | | 20.0% | 20 | Between 30 & 40 minutes | | 21.0% | 21 | Between 40 & 50 minutes | | 7.0% | 7 | Between 50 & 60 minutes | | 14.0% | 14 | More than an hour | | 13.0% | 13 | | 10. What type of roads do you typically use for your commute? | | Response
Percent | Response
Count | Mostly Freeways | | 52.0% | 52 | Mostly Side Roads | | 48.0% | 48 |

References
Seattle? Rainy? Not really (2007). Puget Sound Business Journal, Retrieved May 29, 2012 from http://www.bizjournals.com/seattle/stories/2007/05/14/daily31.html
Cities with the Worst Rush Hours,(2010) Navteq, Retrieved May 29, 2012 from http://corporate.navteq.com/webapps/NewsUserServlet?action=NewsDetail&newsId=948&lang=en&englishonly=false