Thursday, April 11, 2019

incorporating walking and biking into Traffic Impact Studies

  • For developments coming in, we (like everyone else) require traffic studies to be performed for impacts related to streets, traffic and circulation. One of the ideas we are toying with is requiring those studies to have an element of bike/ped data baked in. So we have a more well-rounded answer on why we want this data, I'm curious if your municipality also asks for bike/ped data when traffic studies are required? If you need do ask for this data, what are your primary reasons?
  • This is one of the key areas of improvement for many of our communities. There are so many reasons to reform Transportation Impact Analyses. It shouldn't just be done for development projects either, it should be more inclusive of all capital projects (ideally). The first reason is to improve the analyses is to address the safety performance of our streets using proven countermeasures for reducing risk for people walking and improving access to transit. The second reason is to implement long range mode split goals into our forecasting of transportation demand. In Portland, ideally a new development would be producing 25% bicycle mode split for commute trips. Once you state that as a goal, it makes the agency consider whether the adjacent street should provide a protected bicycle lane adjacent to the development. If the mode split is 8% for people walking to work and 15% for transit, the preparation of the traffic study should complete trip assignment that identifies the paths of the people walking to the development. That necessitates the analysis of intersections to determine whether crossing improvements (beacons, medians, etc) are necessary to insure safe facilities.

    Most of us know how the provision of additional travel lanes for automobiles makes intersections wider and potentially more dangerous for people crossing. So, another recommendation is to inquire whether the City is willing to consider a lower Level of Service (LOS) during the peak hour. In addition, the analysis completed as a part of the Highway Capacity Manual, actually considers the peak 15-minute of traffic flow, so one simple recommendation is to consider eliminating the use of the peak hour factor to reduce the extent that traffic analyses are focused on the worst 15 minutes of the entire day. Truly designing for the 1%!

    As for the data for walking and cycling, many good traffic counting firms already provide the data in their turning movement counts. If they don't, you should specifically request this in your traffic impact study requirements documentation. Once you have this data, an agency could easily do some modification to the Highway Capacity Manual to estimate delay for people walking and cycling. If an agency requires the traffic impact study to conduct an analysis of intersections adjacent to the development to determine whether an enhanced pedestrian crossing is recommended it could be useful.

    The other thing that you could require is aggregating person delay from the Highway Capacity Manual methodologies. By incorporating the delay calculations for the various  HCM methodologies (pedestrian, vehicle, bikes (with modification), and transit), is a concept worth considering. Person delay is a weighted average that utilizes the traditional LOS analysis and other modified HCM procedures to assess walking, cycling, and transit delays. The number of people on the bus would increase the importance of that particular approach to the resulting measure. It can be useful when using existing data, reflecting the people that are using the street currently and for future considerations. The various results from the different modes are aggregated to discern the overall person delay for each signalized intersection.  The future considerations would require assumptions of mode split by the local agency, but this would be consistent with the recommendations contained in the City Planning documentation.

    A few other agencies have policies that have caught my eye:

    San Jose Protected Intersections 
    A Protected Intersection in San Jose is defined as a local intersection for which no further physical improvement is planned. The City declares that these specific intersections, because of the presence of substantial/potential transit improvements, adjacent private development, or a combination of both circumstances will not be modified to accommodate additional traffic and operate at a Level of Service (LOS) D or better. If a proposed development project would cause a significant LOS impact at one or more of the listed Protected Intersections, the proposed development will include construction of specific improvements to other segments of the citywide transportation system, in order to improve system capacity and/or enhance non-auto travel modes.

    San Francisco Incorporation of Vehicle Miles Travel
    The City of San Francisco used intersection LOS as the primary metric to evaluate the performance of roadways until 2016. At that time, the city sought to use a process that better aligned with its existing policies aimed at encouraging more transit use and improving the bicycle and pedestrian systems. After a detailed analysis, the City settled on VMT per capita as a metric to assess the impacts of new development. This new metric encourages development in transit-rich areas and supports higher densities that encourages multimodal tripmaking.

    Fort Collins Multimodal LOS Performance 
    The City of Fort Collins, CO has redefined Level of Service standards for multimodal transportation for use in their community. It is effective because it provides quantitative measures for walking, cycling, and public transit. The City developed these standards because "applying LOS standards to specific sidewalks, for example, would ignore the issue of whether the sidewalk in question is connected to the rest of the pedestrian network". The Fort Collins Multimodal Level of Service Manual establishes standards for each mode, recognizing that "When LOS for automobile mobility falls below identified levels, mitigation will be required to ensure a high degree of accessibility is provided through alternative modes".
    Pedestrian LOS is based on the following three criteria:
    ·       Directness – distance (out of direction) to destinations including transit stops;
    ·       Continuity – measure completeness of the sidewalk system; and
    ·       Street Crossing Safety – uses NCHRP 562 criteria;