Anatomy of a Development Proposal - Part II Predictions of Dormitory Traffic Impacts Unrealistic

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• In Bellingham, Planning, WWU,

Steve Abell guest writes this analysis. He is a resident of Bellingham.

Ambling University Development Group LLC commissioned TranspoGroup, a traffic engineering firm located in Kirkland, WA, to produce a Transportation Impact Analysis, or TIA, for their proposed University Ridge (UR) student housing project. [You can read the report here.] In this document, TranspoGroup attempts to identify the ways occupancy of the new complex will affect the volume and pattern of traffic in the area around it. In order to accomplish this, TranspoGroup creates three traffic scenarios and then combines them into a fourth. First, it surveys existing traffic to develop a base case: in other words, that which is normal today. Second, it estimates new trip generation from the development. [Note: a resident leaving the complex and later returning has made two trips.] Third, it estimates how traffic might be expected to change without the new development, i.e. what does normal growth look like. Fourth, it combines all three to estimate the impact on traffic volume and patterns of a fully occupied development at some point in the future, typically called the horizon year. A TIA is, therefore, largely a prediction of the future. Predicting the future always involves some level of uncertainty, but by incorporating data from reliable sources and realistic assumptions about the specifics of the situation into the prediction, uncertainty can be reduced.

A TIA is not an easy read for an average person. It is loaded with technical language, maps, diagrams, tables, and worksheets. To the credit of TranspoGroup, it included in the report good explanations of many terms used. With patience, a reader can glean from the first 17 pages of text the sources of data and the basis of assumptions, as well as conclusions about whether any adverse traffic impacts will occur. The TranspoGroup TIA concludes on page 17 that “no adverse transportation impacts are anticipated” and therefore no mitigation will be required. In other words, a new college student housing complex with 576 residents can be dropped into a residential neighborhood with mostly narrow, sloping streets, limited provision for pedestrian and bike activity, and no direct access to arterial streets, all without causing any traffic problems whatsoever. Really? This surprising conclusion comes from some odd omissions and faulty assumptions in the TIA.

One of the most glaring omissions is leaving the Byron St./Lincoln St. intersection completely out of the analysis. This omission is not the fault of TranspoGroup. The city Planning Department did not identify this intersection as important enough to be studied. Why not? The report analyzes nine other intersections, but not Byron/Lincoln which, if you look at a map, is on the shortest, most direct route between the UR site and both WWU and northbound I-5. Drivers leaving UR to go to WWU or to get on I-5 north are most likely to take S. 44th St. to Byron, then down Byron to turn left onto Lincoln joining southbound traffic, then either enter the I-5 northbound on-ramp or turn right onto Samish Way to get over the highway to Bill McDonald Way and WWU. With heavy traffic on Lincoln, the left turn from Byron onto Lincoln will be difficult, and likely to back up traffic on Byron. This is not accounted for in the TIA. Moreover, the visibility of northbound Lincoln traffic from the stop sign on Byron is not very good. The right-turn lane for southbound Lincoln traffic at Samish/Lincoln/Elwood is identified in the report as already a Level of Service problem (LOS D) even without new project traffic.

The TIA predicts the number of new trips per day using standard trip generation data from the Institute of Highway Engineers, which is fine, but TranspoGroup uses prediction data for standard mid-rise apartments. By doing this, it uses the figure of 164 units as the factor in trip generation calculations. The housing units at UR will not be standard apartments. For example, there will be 124 units each with four students, and 40 units each with two students, for a total of 576 residents. Unlike residents of standard apartments, every resident of UR will be old enough to own and operate a motor vehicle. The TIA makes the assumption that many of these students will use public transit at the Lincoln Creek Park & Ride to commute to campus. This may or may not be true – it is debatable. The route is easy going downhill to the Park & Ride, but quite steep on the way back to UR. UR residents may not do this unless the weather is good. For most of the normal school year the weather tends to be not so good. Many more students are likely to drive rather than face that uphill walk after a day at school. Some might even drive to and from the Park & Ride, which would still be a traffic problem for the neighborhood. The TIA speculates that the traffic impact fees will be significantly reduced because of “easy” access to public transit. The developer might like to hear that, but this does not seem realistic.

Commuting to campus via bus does not necessarily mean students will not have cars for other purposes. They will need to shop and access services. They will have social lives. Many may have jobs to go to. Using standard apartment data for trip generation calculations and ignoring the impact of 576 potential drivers is simply unrealistic. The whole concept of peak evening rush hour traffic may not be viable as far as students are concerned, yet there is no consideration or even discussion of this in the TIA. It seems clear that 164 unit figure is the wrong factor and using it provides a couple of potentially significant benefits to the developer:

1. It underestimates the total number of trips per day that will be generated by UR, thereby underestimating traffic congestion and the impact on the neighborhood, thus reducing mitigation requirements that might fall on the developer.

2. It may underestimate the number of trips that will occur in the evening peak rush hour. This number is the multiplier for the city’s traffic impact fee of $1925 per evening peak hour trip, thus reducing the cost to the developer.

Another poor assumption involves the scale-up of traffic patterns. The TIA uses actual traffic survey data taken January 9, 2013 to scale up to traffic that includes new UR traffic. This date is practicable, although it is the day after the WWU winter term started and may not be sufficiently representative. There are two aspects to this scale-up. One is that of traffic volume which is already suspect due to using standard apartment data for trip generation calculations. The other aspect is traffic patterns. The presence of 576 students in the neighborhood will severely disrupt patterns that were in place on January 9, 2013. There are problems in the TIA with the predicted distribution of new traffic due to using existing patterns for scale-up. The TIA points out that most of the future residents of UR will be WWU students. Agreed, but then the TIA predicts that only 35% of the traffic from UR will be going to or returning from the WWU campus. They show 45% of UR traffic to or from I-5. WCC and BTC students might use I-5 to get back and forth to their campus, but it is unlikely many WCC or BTC students will live at UR. The distribution needs to favor WWU traffic much more strongly, and reduce UR traffic on I-5. By reducing WWU traffic to 35%, the impact on the intersections on the east and west sides of I-5 along Samish Way is minimized. With a more realistic distribution of new traffic, an already busy set of intersections will get worse. If you pass through these intersections in the morning or evening you already know the scenario. Imagine more cars, bikes, and pedestrians using these intersections.

Neither the professionalism nor the competence of TranspoGroup is in question here. They fulfilled the assignment given to them by the developer, its agents, and the city. However, the TIA appears to use some unrealistic assumptions and erroneous choices of support data. This leads to the faulty conclusions that no adverse traffic impacts will occur and no mitigation will be needed. To summarize:

1. An important intersection, Byron/Lincoln, on the most direct route between UR and both WWU and northbound I-5, is ignored in the analysis.

2. Trip generation factors for standard apartments are used to predict added trips from UR. This ignores the nature of future UR residents and underestimates trip generation.

3. Traffic patterns and distribution are scaled up from existing patterns, but UR will dramatically change patterns, making the scale-up questionable. Not enough new UR traffic is assigned to the route to and from WWU, and too much is assigned to I-5.

4. The TIA estimates that a significant number of UR residents will take public transit and walk or bike back and forth to the Lincoln Park & Ride. Even if true, which is questionable, this will have little impact on the number of UR residents who own and operate vehicles.

Our city Planning Department must now take the lead in addressing these issues and moving the TIA conclusions closer to reality.

About Guest Writer

Citizen Journalist • Member since Jun 15, 2008

Guest Writer is for over 100 articles by individuals who are not regular writers. Their actual name and brief info is listed at the top or bottom of their articles.

Comments by Readers

Tip Johnson

Jul 03, 2013

If our infill toolkit included better detached accessory housing provisions, we would probably not even need this type of development.  Plus, students wouldn’t be bunched up in ‘Animal House’ environments, but rather more evenly distributed and somewhat better supervised by their principal dwellings and neighbors.


Dick Conoboy

Jul 04, 2013


I would tend to agree with you if the city were willing to enforce even its current laws on ADUs.  Sadly, this is not the case, as you well know.  Let the city clean up its act on its current ordinance on ADUs and I will gladly support the increased use of ADUs. 

The acreage in question here is very much suitable for use as an infill tool kit development with a slightly increased density over the surrounding area instead of the massive imposition of a four building complex with density of about 100+ individuals per acre.

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