Data

The calculator relies on data collected by the Maryland Department of Transportation (MDOT) and publicly available at: https://roads.maryland.gov/mdotsha/Pages/index.aspx?PageId=302 . Data is available in either Excel or pdf format.

The data provide estimates of road mileage and annual VMT by county for seven functional classifications of roads in urban areas and an additional seven for rural areas. Functional classifications define the type of service provided by a road, for example a freeway, turnpike, or expressway allows for higher speeds and will accommodate more vehicles per hour compared to an arterial road, which will have traffic signals and lower speeds. At the far extreme are local roads with low speed limits that serve final destinations, such as residential and local commercial areas.

We combined some of the road classifications to minimize those instances in which there were zero road miles (for example, many of the more urbanized counties had no roads classified as rural or had minimal miles of roads under that category). We combined interstates with principal arterials/freeways/expressways as these both largely have identical road designs, including being largely controlled access highways. We also combined major and minor collector roads into one category. In total we have five road categories for both urban and rural roads in the calculator. The data includes both annual vehicle miles of travel and lane miles for each road type for all 23 counties plus Baltimore City (which is equivalent to a county jurisdiction).

Our first year of data is 2017 and we will update to the latest year available. Caution should be used when analyzing data and interpreting results for 2020 and 2021 due to changes in travel patterns due to the COVID pandemic.

We also include an estimate of CO2 equivalent emissions. This is estimated based on the average on-road transportation CO2 equivalent emissions per mile for the entire state which is 361.5 grams/mile. Data on total state on-road transportation emissions was taken from the Maryland Greenhouse Gas Inventory using 2020 data.

Elasticity assumptions in the calculator are shown in the table for each road classification. In general, the empirical evidence suggests that larger higher speed roads have a larger elasticity. We have included a range and the calculator output provides a range of estimates for induced VMT. Given the potential range of estimates and variation in how VMT may be affected, we have included a “back-calculator” which allows the estimation of an “implied elasticity” based on forecast growth in VMT associated with a capacity expansion. This can be thought of as the elasticity implied by any forecasts of travel done by a state DOT or a local agency promoting the capacity expansion. The assumption often made, is that there is no change in VMT attributable to the expansion, despite the evidence for induced travel. The user of the calculator is thus able to assess whether estimates made in forecasts are reasonable.