SANDAG Transportation Resources

SANDAG Senior Research Analyst Mike Calandra sent us some traffic data updates for our Data As a Public Good report. I’m always thrilled when I get to communicate directly with agency analysts, and having them write to me is like an early Christmas.

In our Data as a Public Good report several interviewees reported that they had difficulty getting traffic data from SANDAG, and the SANDAG website only publishes traffic count data as a PDF or an interactive map. However, SANDAG was very responsive to my Public Records Act Request for the traffic counts in a structured format, and we’ve got the response from that request in our repository, so we’ve updated the report to reflect this more recent experience, and here are some other resources that Mike mentioned.

SANDAG is current in the process of updating their traffic count reports and replacing them with a Regional Count Database. The application will be an interactive map with a focus on arterial streets. CalTRANS, through their PEMS application, reports counts for  freeways. PEMS also has about 10 years of data for many other traffic metrics, such as collisions.

Every 10 years, SANDAG does a survey of county residents about travel. The last one was conducted in 2006. I haven’t read the report in enough detail to assess the quality of the statistics, but I’m already really impressed with the design and methodology – see “Cognitive Interview” appendix on page 132 for a lesson on how to do a survey right. If the survey company, NUSTATS, put as much work into statistics that they did in designing the survey, this report has the best data it would be possible to get.

Mike sent a few other links that I knew existed, but hadn’t seen, such as these links to forecasts:

One of the most important datasets that SANDAG produces is their traffic model and the forecasts that the model produces. Every Metropolitan Planning Organization produces traffic forecasts and analysis, since that is the job they were created to do.  If you’ve followed recent local news, the use and publication of this model has been contentious, and two of our interviewees for the Data as a Public Good report said that SANDAG would not release model inputs and output because they considered them proprietary software, an assertion confirmed by letters from lawyers we’ve seen in SANDAG PRA requests.

However, it looks like this may be changing in response to SB 375 – see ‘contentious’, above – which requires MPOs to update their model capabilities, a project that SANDAG embarked on in 2009. These improvements, along with SANDAG’s long term involvement in the CalPECAS peer group and its transition from the 4 Step Model to the Activity Based Model should mean that the resulting models are more open and ultimately more useful to analysts outside of SANDAG.

Traffic models can be spectacularly complicated, and it is really difficult for average data users to interpret the models, verify that they make sense, and use the results. Having them be closed to public inspection means they are more likely to have errors, so making models more open and available will mean that more of those inevitable errors will be found and corrected. I hope the trends toward openness continue, because I’m very interested in having the San Diego Regional Data Library contribute to model improvements that wil benefit the whole region.