Trip-generation Rates: Innovations in Storm Water Infrastructure Funding

July 30, 2021

Climate change has increased the need to address aging storm water infrastructure, and trip-generation rates offer a  solution to fund improvements

Responding to and making appropriate adaptations for climate change is a pressing issue for local governments and one that will take a considerable amount of time, energy, and funding to tackle. When it comes to water utilities, especially in the instance of storm water, the unpredictable nature, size and frequency of storm events, plus impending sea level rise has put a strain on already aging infrastructure, requiring huge investments to address the problem. 
Relying upon funding methods of the past to pay for these investments isn’t going to cut it. In most cases and communities, an entire paradigm shift is going to be the only way forward. Using data like trip-generation rates to develop a hybrid model of assessing fees is an innovative and equitable solution that can benefit communities and just one example of ideas that are on the table. 

A New Approach to Storm Water Fees

Typically, storm water fees are determined by impervious areas—the footprint of property that cannot absorb water. These show up as part of monthly utility bills or yearly property tax assessments. Impervious areas block the natural infiltration of storm water into the ground and results in higher runoff that must be managed by the municipal storm  water system. Larger structures or more pavement usually leads to a higher fee assessed. While that may seem like a fair method of calculating fees, every city is different. Vertical development and high population densities have challenged the usual model of fee collection, exposing proportional benefit gaps among property types and usage.

In Fort Lauderdale, Florida, for example, storm water issues have primarily affected roadways, forcing the city to focus its efforts on keeping roads clear and passable while enhancing the quality of storm water through street sweeping. The city’s fee structure did not accurately reflect benefits to residents of usable streets from storm water infrastructure. This meant much of the cost burden fell on a smaller fraction of the city’s residents, while the benefits are accrued more broadly. Working with city officials, Stantec developed a hybrid model using a trip-generation rate component for storm water fees that would better reflect the estimate of a given plot’s roadway use and create a more equitable system.

What is Trip Generation?

The Institute of Transportation Engineers creates trip-generation rates from extensive survey data.They estimate the average number of daily trips a parcel generates. A single-family home averages around 9 trips per day, while a gas station averages 845 trips per thousand square feet of store. Commercial properties generate trips due to the high activity that takes place on the land. This, in turn, leads to a greater benefit of clear and passable roads than a similar size plot generating fewer trips. Additionally, trip-generation rates are measured in one of two units: 1) the building square footage, or 2) the number of trip demand units (dwelling units). Those two measurements consider a parcel’s whole development, including the vertical built environment. This change is a significant contrast to traditional measurements that only considered impervious areas, which is basically a 2D variable. 

Consider this – the impervious area of two plots can be identical, but one is a single-story building with 15 residential units and the other is a multi-story building with 300 residential units. Looking at only the measured impervious area, one could conclude the two plots benefit the same from storm water services. However, the plot with more residential units generates significantly more trips and receives more benefit in total than the plot with a lower use of the roadway network—the primary place where storm water actives occur. 

When you consider the steps a city takes to address storm water issues to maintain free and passable roadways, it is evident the parcels benefit far differently. By expanding our thinking to consider how the roadway network is being used, we can create a fee schedule that better reflects the benefits of storm water activities to provide a fairer and more equitable plan.

Power of the People

Perhaps the most critical element to applying an innovative fee structure is community support. People are naturally resistant to change, especially when it involves increased costs. Engagement is essential for helping residents understand that they are part of a larger community. Helping the residents grasp how their community’s systems are linked can reduce the resistance to fee increases that support quality-of-life services.
In Fort Lauderdale, the team participated in nine public meetings. Part of Stantec’s strategy was to find community champions that could convince their neighbors the changes were needed. Since the fee increase affected high-rise residences and commercial properties more, they  scheduled special meetings to discuss the increased benefits of storm water management to the residents.

Unique Solutions are Just That, Unique

A cookie-cutter approach to storm water funding will not work for most communities. Each has their own distinctive traits and needs. Thus, solutions must address local challenges. While trip-generation rates made sense for Fort Lauderdale, they may not work for another city. For example, in the city of Venice on the opposite coast of Florida, red tide events and algae blooms can cause infrastructure issues. In that case, Stantec suggested a water-quality element to the city’s fees meant to help reduce the impact of storm water pollution on local waterways. The water quality of the discharge can be measured and assessed at an appropriate fee to provide an equitable solution for this community. 
There are many combinations of solutions available to produce a fair and equitable fee structure. By working with stakeholders to understand the community’s problems, we can align the solutions available to make sure the fee reflects the area needs.

About the Author

Kyle Stevens