SDDOT currently has a limited number of traffic engineers trained in traffic projections, traffic assignments,
and distribution techniques. It therefore relies on consultants to provide this information for corridor
studies, site impact studies, and long range planning efforts. The SDDOT Long Range Transportation Plan is
over seven yeard old, is based on policy rather than projects, and will need to be updated within the next
few years. In addition, freight impacts are not well documented and economic development issues are addressed
individually without analyzing traffic pattern changes in the state highway network.
A better understanding of travel patterns within the state will lead to improved highway planning and
ultimately to a highway network better suited for South Dakotas economic future. The SDDOT needs the capability
to analyze route diversion impacts prior to corridor improvements. The department also needs the ability
to analyze the capacity and safety impacts associated with increased or diverted truck travel on state routes
due to the introduction of new inter-modal facilities adjacent to highways. A review of department policies,
processes, resources and other requirements is needed to determine if a statewide traffic forecasting model
should be developed, or if other alternatives that might involve training, additional staff, or consultants
could meet its travel demand forecasting needs. Finally, a review of the existing travel demand forecasting
process needs to be completed to determine if the forecasted factors accurately reflect traffic volumes for the
various functionally classified roadways.
Findings: The purpose of this research study was to evaluate the most appropriate traffic forecasting tool that is most responsive to the needs of the South Dakota Department of Transportation (SDDOT). Like many other state agencies, the SDDOT has to do more with less funding for transportation infrastructure, operation, maintenance, and planning. The traffic forecasting functionality had to be tailored to SDDOT's needs and constraints while maximizing benefits.
The interviews of SDDOT stakeholders strongly emphasized the desire for a better forecasting approach than the current 20-year traffic forecasting procedure. The research team evaluated the uses/ needs of traffic forecasts at SDDOT against the availability of data, budget, and staff. While it is possible to build a statewide travel model (STM) of sketch planning type using available data, the applicability of such a model would fall short of meeting many of the identified uses and needs that are largely project specific. However, building a more robust 4-step STM that would satisfy many of the uses/ needs requires travel behavior data currently unavailable. Considering the advantages and disadvantages, the research team did not recommend a four-step statewide model at this stage. A more practical approach in the short-term is to enhance the current 20-year traffic forecasting procedure, use of GIS and transportation planning software, and staff training in travel demand forecasting. A sketch planning type STM was recommended in the short-medium term together with future enhancements that include a regional model option and 4-step STM for passenger and freight.