California Department of Transportation

Statistical Analysis Support


This Branch advises on or performs statistical analysis for a variety of projects, such as the design and monitoring of travel surveys and statistical analysis of demographic and travel data (survey and model). It also supports licensing and use of SAS© software in Caltrans. SAS is an extraordinarily comprehensive analytical software suite that exchanges data with multiple applications. It permits utilization of sophisticated graphical, statistical and operations-research methods.

2008-9 National Household Travel Survey Data with California Add-Ons

The Federal Highway Administration’s National Household Travel Survey (NHTS) team contracted to conduct a national household travel survey in 2008-9. NHTS invited state DOTs to have the sampling in their areas augmented; Caltrans did so, allocating funds to survey an additional 18,000 households statewide (uniformly, except more intensively in San Diego County).  NHTS (FHWA) continues to support use of the national data and the add-ons with the ongoing FHWA Highway Community Exchange and through their very comprehensive website. A masked and aggregated (for respondent confidentiality) form of the national data set is there, and the website has a point and click table and chart building capability.
NHTS transmitted the fully detailed (except explicit respondent identifiers) and quality assured California data sets with weights to Caltrans. They are maintained, analyzed and distributed by this branch. For more detail and a request package go to: NHTS Data.

Automotive Impacts Estimation (Air Pollutant Emissions and Fuel Consumption

The Direct Travel Impact Model (DTIM) reads travel estimates from network transportation modeling trip assignment files (link volumes and zonal trip ends) and automotive air pollutant emission and fuel consumption rates from The California Air Resources Board emissions/fuel consumption rate model EMFAC (Emission Factors).  DTIM then calculates air pollutant emissions (including greenhouse gasses) and fuel consumption amounts then reports them in a variety of forms and levels of detail:

  • Region totals for transportation plan evaluations
  • County totals for State (air quality) Implementation Plan (SIP) reports (ARB uses the additional “Burden” part of EMFAC for “official” SIP Conformity Findings)
  • Road segment and zonal for project level studies
  • Gridded, diurnal for photochemical models

Direct Travel Impact Model Fact Sheet

Direct Travel Impact Model 4 (DTIM4)  User's Guide (April 2001 version)


Leonard Seitz,