A Reminder of How to Access and Customize Your Analysis of the NHTS Data

The URL is http://nhts.ornl.gov.

Click on the Online Analysis / Create a Table menu.

Log in by providing your email address and password.

Select the Analysis Variable, i.e. the data you want in the table cells. Note that not all possible Analysis Variables are listed, e.g. person trip rates per household per day. For these applications, you must run persons trips in one table, households in the other, and divided the two. All travel day information you get from the NHTS Web site will be in terms of annual data – to get daily, simply divide by 365.

Also note that there are some cross tabs that cannot be prepared using the Web analysis engine.

Select the Type of Table option, One-way, Two-way or Three-way. Note that when preparing a three-way table, and IF all other things are equal, use the variable with the least number of categories as the page variable. 

Select your row, column and, if appropriate, page variables. Note that one of the benefits and challenges of using NHTS is that there may be several variables for the same data (e.g., annual miles driven can be calculated using travel day trips, the drivers annual mileage estimate or the BESTMILE estimate for the vehicle that this driver is the primary driver of). There is redundancy built in to many of our estimates – you are not imagining this.

To subset the dataset, i.e. you want only walk trips, you must first turn on the option: click on Options at the top – click on Subgroup and Add. Then, go to the Subgroup window at the bottom of the table specs and follow the instructions. In this case it would be TRPTRANS EQ ‘26’. Use the green plus sign to the right of the window on the subgroup page to have it show your choices. You must make sure the subgroup statement you want appears in the Edit Subgroup Statement window and that, after editing when necessary, you Save it. The subgroup statement must show up on your table specs window or else it is not active.

To change the categories within a variable, click on Options at the top – click on Variable Categories, and Define. This will give you a window to restructure how the categories are used in your table. Once you have refined and saved a variable’s categories, you can reuse them later.

What if you forget to define categories for a variable that has a huge number of responses, like trip length? The Web tool will provide our pre-defined categories for these. No, you will not get a table with each possible trip length. However, there are some variables that do not get pre-categorized, such as number of people on the trip. To see how your variable will look in a table, when you go to the Variable Browser to select a variable, there is a table to the right which will provide the Codebook information, including default variable categories.

Look for the small blue book icon next to variables; click on the book to see the Codebook page for that variable.

Once you run the table, click on Output Area to get the table displayed. From there you can print it or download it to an Excel spreadsheet. Note than when downloaded to Excel, you need to unmerge the column headers from the first line of data.  

If you are running a series of tables, the Table Specs window will always keep the last table you ran, until you change it.