Travel Demand Model looks into the future
By Chris Daley
From page A1 | July 09, 2012 | Mountain Democrat

El Dorado County Supervisors insisted that their goal is to “make things easier” as they plan for future growth and development. Specifically, they were considering the county’s “Travel Demand Model,” which attempts to forecast residents’ driving patterns over the next 25 years. The model is required for ongoing implementation of the county’s General Plan.

Engineers with the El Dorado County Department of Transportation discussed and displayed a Roadway Network Map and Traffic Analysis Zone Map for the board recently. The project is being conducted by county staff and the Sacramento branch of Kimley-Horn and Associates consulting firm.
In order to plan rationally for the county’s future travel needs, the department and KHA needed to develop baseline data for which it used the year 2010 as the starting point. The Roadway Network data provide a “basis for estimating travel time between Traffic Analysis Zones (TAZ) and as a basis for traffic assignments,” according to DOT’s documentation.

That information further serves as a “tool to facilitate an understanding of how trips are distributed and as a tool for displaying the level of traffic congestion associated with different land-use scenarios.” The model is based upon projections stretching  out to the year 2035.

Potential land use is what drives the planning component issues of which traffic is a significant element. In engineering parlance, the TAZs “provide the basic unit for converting spatial area data into tabular data for use by the Travel Demand Model.”

Those data are used to “manage interactions between internal land uses and for channeling trip loading onto the model roadway network,” the documents explain. In simple terms, the model projects the amount of traffic expected to impact a given area, for example, if a subdivision of 200 homes is built in the neighborhood.
The TAZs also are used to gather  and “display information relating to land use, employment, population, socio-economic and other data.”

DOT senior civil engineer Claudia Wade and Natalie Porter gave a slide presentation describing the project’s plans and goals. The Roadway Network in part attempts to predict “how feeder roads impact our roads,” Wade said.
Feeder roads would be any roads that lead motorists in to or away from a specific area thereby causing some traffic impact on that area’s roads and streets. Traffic coming out of Folsom on Green Valley Road, thus could have a measurable impact on residential and commercial development on the north side of El Dorado Hills as well as in Cameron Park and the Rescue area, Wade explained.
Traffic Analysis Zones are based on a “gravity model,” Wade said. That is that drivers will use the “shortest and quickest way to get to where they’re going.”

As proposed, there will be 626 TAZs included in the model, and their function “should be understandable to the public,” she added. That concept resonated with supervisors who acknowledged that the material is highly technical because it is a piece of a much larger puzzle, that is the General Plan. And that plan includes a host of interrelated issues from traffic to housing to employment to aesthetics and areas of historical significance as well as government services.

Supervisor Jack Sweeney urged that the project needs to be presented so “the public can understand, in plain English. This is a wonderful technical document but the public is missing the point of what we’re trying to do here. I want the deliverable here, clearly defined.”

Sweeney also railed against the county’s policies that can require any applicant for permits to do a traffic study.
Supervisors Ron Briggs and Ray Nutting also took pokes at the complexity of the project and its methodology. Briggs had noted earlier that “our goal is to make things easier.”

“I’m trying to get this down to an understandable level,” Nutting said regarding how the study ascertains numbers of vehicle trips in all regions of the county. “So the closer you are to services, the more trips you take?” he asked.
“Yes,” co-presenter Porter responded.

More technical work remains to be done on the mapping project. Public comment has been gathered particularly from the county’s TIM Fee Working Group (Traffic Impact Mitigation) and the Engineering Subcommittee of the Economic Development Advisory Committee. And the board will hold a hearing to finalize the proposed maps on July 24.